DIAMOND GRADING

Lab Manual
CONTENTS
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Diamond Grading Tools and Equipment . . . . . . . . . . . . . . . . . . . . . . . 7

Carat Weight and Size. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Clarity Grading. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Cut Grading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

Color Grading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183

Grading Fancy Cuts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215

Grading Mounted Diamonds. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255

Treatments, Synthetics, and Simulants . . . . . . . . . . . . . . . . . . . . . . 281

Acknowledgements
The Gemological Institute of America
gratefully acknowledges the following people
for their participation in the preparation of this
lab manual:

Technical Assistance
Al Gilbertson, Brenda Harwick, Brooke Goedert,
Ilene Reinitz, PhD, Wuyi Wang, PhD

Photo Courtesies
Cathy Jonathan, 270; GemOro Superior
Instruments, 317; John O’Hara, 276;
Kathryn Kimmel, 272; Lauren Stomel
Advertising, 269 (left); Rogel & Co., Inc, 90;
Rose Tozer, 273; WorkingSilver.com, 35 (left)

Cover Photos by: Kevin Schumacher/GIA (top);

Robert Weldon/GIA (middle); bottom from left:
Kevin Schumacher & Robert Weldon/GIA,
Denise Conrad/GIA, Eric Welch/GIA,
John Koivula/GIA, GIA, Robert Weldon/GIA,
Denise Conrad/GIA, Denise Conrad/GIA,
Shane McClure/GIA

Facing page: Each diamond has its own

combination of qualities that distinguish it
from other diamonds. The grading skills you’ll
learn in this manual will give you a deeper
understanding of those qualities and how to
evaluate them.

©
©2014 The Gemological Institute of America
All rights reserved: Protected under the Berne
Convention.
No part of this work may be copied, reproduced,
transferred, or transmitted in any form or by any
means whatsoever without the express written
permission of GIA.
Kevin Schumacher/GIA

DIAMOND G RADING LAB MANUAL

This lab manual provides a clear and systematic way to evaluate diamond quality using
the GIA International Diamond Grading System™. This system rates the Four Cs of
diamond quality—carat weight, cut, clarity, and color—and provides a universal
language for discussing diamonds and comparing one diamond to another.

THE FOUR CS
Following is a brief description of each of the Four Cs of diamond quality. You’ll find
detailed grading instructions for each one in later sections of this manual.

©2014 GIA. All rights reserved. 1

 DIAMOND GRADING LAB MANUAL

Carat Weight
The weight of a diamond—its carat weight—is measured in metric carats.
One carat equals one-fifth of a gram (0.200 g).
0.50 ct. 0.75 ct. 1.00 ct. 2.00 cts. 5.00 cts.

Diamond weights are stated in metric

carats. Cut
A diamond’s cut can mean simply its shape and cutting style (facet pattern).
There are many different diamond cuts. By far, the most common is the
round brilliant, which is round with triangular, kite-shaped facets that radiate
out from the center. Diamonds with shapes or cutting styles other than the
round brilliant are called fancy cuts.
In diamond grading, cut also refers to a diamond’s overall cut quality. Cut
evaluation includes an assessment of the diamond’s proportions, the
symmetry of its outline, the placement of its facets, and how well each facet’s
surface is polished. For round brilliant diamonds that fall within the normal
color range, described on page 3, cut is graded on a relative scale from
Excellent to Poor.

Robert Weldon/GIA
Popular diamond cuts include (left to right) round brilliant, radiant, oval,
emerald, and pear cuts.

Star length
Table size
Crown
Crown height angle
Girdle thickness

Total depth Pavilion

angle
Pavilion depth

Lower half length

Culet size

Evaluation of a diamond’s cut includes an analysis of its proportions (left), symmetry (right), and
polish.

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 DIAMOND GRADING LAB MANUAL

Clarity
Clarity is the relative absence of inclusions and blemishes, collectively called
clarity characteristics. Inclusions are internal characteristics, while blemishes
are confined to the surface. Clarity is graded on a relative scale from Flawless
(with no inclusions or blemishes visible at 10X magnification) to Included
(with inclusions obvious at 10X magnification).

Diamond clarity is
graded on a relative
scale from Flawless
(left) to Included
(right).

Color
Color refers to the amount of basic color—called bodycolor—in a diamond.
Bodycolor can vary in hue, tone, and saturation. Most diamonds used in
jewelry range from colorless to light yellow and brown. Diamond color is
graded on a scale from D (colorless) to Z (light yellow, brown, or gray),
referred to as the normal color range. Diamonds in deeper shades of yellow,
brown, and gray as well as diamonds in colors such as blue, green, and pink,
are referred to as colored diamonds.

Kevin Schumacher and Robert Weldon/GIA

Diamonds can range from colorless to deep colors such as pinks and blues.

3
DIAMOND GRADING LAB MANUAL

Facet Arrangement of a Standard Round Brilliant

Table Number of Facets

Table 1
Bezel facet
Bezel 8

Star facet Star 8

Upper Half 16
Upper half facet
Pavilion Main 8
Crown
Lower Half 16

Girdle Culet 0 or 1

Total 57 or 58
Culet
Pavilion

This illustration shows the parts of the

Lower half facet standard round brilliant and the terms
used to describe them. As you learn the
basics of diamond grading, the focus will
be on the round brilliant, as it is the most
common diamond cut. Later in this
Pavilion main facet manual, you’ll learn to apply diamond
grading methods to fancy cuts.
Peter Johnston/GIA

Crown—Top part of a faceted gem, above the girdle.

Table facet—Facet at the top of the crown; usually the largest facet on
the stone.
Upper half facets—Facets that extend from the girdle edge toward the
table.
Bezel facets—Kite- or diamond-shaped facets between the table and the
girdle.
Star facets—Facets that extend from the table edge toward the girdle.
Girdle—Narrow section that forms the boundary between a stone’s crown
and pavilion.
Lower half facets—Facets that extend from the girdle edge toward the
culet.
Pavilion—Lower part of a faceted gem, below the girdle.
Pavilion main facets—Kite- or diamond-shaped facets between the girdle
and the culet.
Culet—Small facet at the bottom of the diamond, where the pavilion mains
meet. Its purpose is to protect loose diamonds against abrasion and chipping.

4
 DIAMOND GRADING LAB MANUAL

Diamond Grading Worksheet

This worksheet is designed for your use in the classroom to document the grading features of round
brilliant diamonds. To maximize your learning experience, you will record more of the diamond’s details
than would normally be recorded by the trade or listed on a grading report.

DIAMOND GRADING WORKSHEET — ROUND BRILLIANT

Name: ____________________________________________

R1-101
Stone No.: ________________________________________

CARAT WEIGHT: ___________________________________

0.38 ct.

4.57 – ___________
Measurements: ___________ 4.60 x ___________
2.88 mm
min. diameter max. diameter depth

4.585 mm
Average Diameter: __________

GIA 1234567890
Inscription: ________________________________________

Cut Estimation Factors: Visual Appearance

Brightness. . . . . . . . . . . . . . . . . . . . . . . . . . . EX VG G F P

Pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . EX VG G F P
EX VG G F P
Fire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Proportions and Design

9
Overweight . . . . . . . . . . . . . . . . ________% EX VG G F

62.8
Total Depth . . . . . . . . . . . . . . . . ________% EX VG G F P

2.65 mm, ________%

Table . . . . . . . ________ 58 EX VG G F P
EX VG G

Key to Symbols:
55
Star Facet . . . . . . . . . . . . . . . . . ________%
35.5
Crown Angle . . . . . . . . . . . . . . . ________° EX VG G F P

15.0
Crown Height. . . . . . . . . . . . . . . ________% EX VG G F P
XUM
________________________
NON
Culet Size . . . . . . . . . . . . . . . . . ________ EX VG G F P
NEM
________________________
43.5
Pavilion Depth _______%, 41.2
Angle ________° EX VG G F P

80
Lower Half . . . . . . . . . . . . . . . . . ________% EX VG G CME
________________________
4.5
Girdle Thickness . . . . . . . . . . . . ________% EX VG G F P
________________________
THN to _______
_______ MED , ______________
Fac EX VG G F
min. max. condition ________________________
Painting/Digging Out. . . . . . . . . . . . . . . . . . . EX VG G F
EX VG G F P ________________________
Combined Proportions (T/C/P Table) . . . . . .

Finish ________________________
VG
Polish. . . . . . . . . . . . . . . . . . . . . ________ EX VG G P ________________________
rating

TP, Wht
___________________________________
________________________
features
________________________
VG
Symmetry . . . . . . . . . . . . . . . . . ________ EX VG G P
rating ________________________
T/oc, C/oc
___________________________________
features ________________________

CUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ________
VG Comments:
grade

CLARITY ________________________________________________
_________________________________
Pinpoints are not shown.
minor inclusions VS1
________
descriptor grade _________________________________
COLOR __________________________________________________
near colorless H
________ _________________________________
descriptor grade
_________________________________
medium
Fluorescence __________________________ blue
___________________________
intensity color _________________________________
p/n 111660 © 2014 GIA _________________________________

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DIAMOND GRADING LAB MANUAL

GIA Diamond Grading Report™

The GIA Diamond Grading Report™ includes a full assessment of the diamond’s Four Cs along with a
plotted clarity diagram. It’s available for loose diamonds in the D-to-Z color range.

6
 TOOLS AND EQUIPMENT
DIAMOND GRADING
DIAMOND G RADING TOOLS AND EQUIPMENT 7
Gemcloth 7
Tweezers 9
Girdle-to-girdle: Hard-surface Pick-up 9
Table-to-culet: Soft-surface Pick-up 11
Stoneholder 12
Microscope 14
Components 14
Focusing the Microscope 15
Types of Lighting 16
Loupe 17
Louping Environment 17
How to Loupe 18
Pointer Probe 21
Water-grading Tools 22
Soap-and-water Solution 22
Cleaning and Turning the Diamond 22
Stone Papers 23
Unfolding 23
Folding 24
DIAMOND G RADING TOOLS AND
EQUIPMENT
This section describes the basic gemological tools and equipment used for
grading diamonds.

GEMCLOTH
You use a gemcloth to clean the diamond before and during grading. The
gemcloth has two sides, one rough and one smooth. Keep your gemcloth
folded with its rough surface on the inside. That’s the side you will use to
clean the diamond.

Smooth side

Rough side

Denise Conrad/GIA
A gemcloth has a rough side and a smooth side. To use the cloth to clean a diamond,
fold it so the rough surface is on the inside.

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DIAMOND GRADING LAB MANUAL

To clean a diamond:
1. Place the diamond inside the folded cloth.
Be careful not to touch the inside of the gemcloth, as this can
transfer grease or dirt to its surface.

2. Rub the diamond firmly in the cloth to clean it.

3. To keep the diamond clean, use either tweezers or a stoneholder—
not your fingers—to pick it up.

1 2 3
All by Denise Conrad/GIA

In order to clean the diamond effectively, the gemcloth itself must be clean.
Therefore, you should wash your gemcloth regularly.

To wash your gemcloth:

1. Use a small amount of detergent and water.
Be sure to use detergent that is free of lotions and contains no fabric
softener.

2. Rinse the gemcloth thoroughly, wring it out, and hang it to dry.

8
 DIAMOND GRADING LAB MANUAL

TWEEZERS 1
Tweezers are used to hold the diamond during grading. Depending on the
view you need, you can hold a diamond in the girdle-to-girdle or table-to-
culet position.

Girdle-to-girdle: Hard-surface Pick-up

To hold a diamond in the girdle-to-girdle position, you will use a “hard-
surface” pick-up.

These are the steps to follow:

1. Pick up the tweezers with the tips of your fingers. 2

Hold the tweezers in the middle. It’s difficult to pick up and hold
the diamond if you hold the tweezers too close to either end.
2. Place the diamond table-down on a table or other clean, hard
surface. With the tweezers parallel to the diamond’s table, slide the
tips around both sides of the diamond.
3. Apply slight pressure and gently pick up the stone.
• Use only slight pressure, just enough to hold the diamond 3
securely. Applying too much pressure can damage the diamond
or cause it to pop out of the tweezers. It can also cause wrist
strain.
• Make sure that a little less than half of the diamond extends
beyond the end of the tweezers. This will allow the maximum
amount of light to penetrate the diamond and also reduce tweezer
reflections, making it possible to see most inclusions clearly.

All by Denise Conrad/GIA

9
DIAMOND GRADING LAB MANUAL

4. When using tweezers in the microscope, rest them against the stage
for stability and to allow more light into the diamond.
Use your non-writing hand so your writing hand is free to document
grading details.

Denise Conrad/GIA

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 DIAMOND GRADING LAB MANUAL

Table-to-culet: Soft-surface Pick-up

To hold a diamond in the table-to-culet position, you will use a “soft-surface”
pick-up.

These are the steps to follow:

1. Place the diamond table-down on a gemcloth.
2. Slide one tip of the tweezers under the diamond until it is centered
under the table.
3. Close the tweezers and gently pick up the stone. Again, use only
slight pressure to hold the diamond.

1 2 3

All by Denise Conrad/GIA

NOTE:
Be sure to place the culet near the end of the tweezers
so a little less than half of the diamond extends beyond
the end of the tweezers.

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DIAMOND GRADING LAB MANUAL

STONEHOLDER
The stoneholder is another useful tool for holding the diamond during grading.

Advantages:
• Attaches to the microscope, reducing strain caused by holding
tweezers for a long period of time.
• Allows for easy set-up when you’re showing and discussing a
diamond’s characteristics with another person.
• Reduces risk of damage because it places less pressure on the diamond.

Disadvantages:
• Stones can pop out and be lost.
• When used with smaller diamonds, the stoneholder covers too
much of the diamond, making it difficult to see inside.
To hold a diamond with a stoneholder in the table-to-culet position, you will
use the “soft-surface” pick-up technique as follows:
1. Place the diamond table-down on a gemcloth.
2. Open the stoneholder and carefully slide the bottom prong under
the diamond until it is centered under the table.
3. Allow the stoneholder to close slowly around the diamond’s culet,
then pick up the diamond.
To make sure the stone is securely seated in the holder, run the
diamond along the gemcloth so it rotates in the holder.

4. Attach the stoneholder to the microscope.

1 2

3 4
All by Denise Conrad/GIA

12
 DIAMOND GRADING LAB MANUAL

5. To manipulate the diamond during grading, grip the stoneholder

near the diamond and hold the diamond close to the well.
• This set-up allows you to easily rotate the diamond from the
pavilion to the girdle edge and on to the crown view. It also
allows you to make the subtle movements needed to focus in
and out of the diamond.
• If you grip the stoneholder at the end, you will have far less
control over subtle movements. This will make it difficult to
grade the diamond.
• If you hold the diamond too far from the well, less light will enter
the diamond, making it difficult to locate minute inclusions.

Correct Incorrect
Both by Kevin Schumacher/GIA

Correct Incorrect
Both by Valerie Power/GIA

13
DIAMOND GRADING LAB MANUAL

MICROSCOPE
During the grading process, you will use a stereo binocular microscope to
locate and identify clarity characteristics and treatments, and to evaluate
proportions. You will also use the microscope along with a 10X loupe to
evaluate clarity, polish, and symmetry.

Components
There are various makes and models of stereo binocular microscopes, but
they all have the same basic components.

Iris diaphragm
Fine focus adjustment ring open-close

Baffle
POD
Oculars
Kevin Schumacher/GIA

Baffle open-close
Overhead light source
Variable zoom knob

Focus knob
NECK
Well

Stage

BASE

Well light control

Eric Welch/GIA
It’s important to learn the parts of a gemological microscope and how to operate
them. A close-up (top right) shows the baffle and iris diaphragm.

14
 DIAMOND GRADING LAB MANUAL

Focusing the Microscope

It is important to focus your microscope properly so you can clearly see the
diamond’s characteristics and also reduce any possibility of eye strain. If
you use corrective lenses, wear them when you use the microscope. Do not
wear your reading glasses, however.

To focus the microscope and adjust it to your eyes:

1. Turn on the well light to its maximum brightness (100%).
2. Close the baffle and iris diaphragm.
3. Turn the variable zoom knob to its lowest magnification.
4. Use the focus knob to focus on the edges of the iris diaphragm.
If necessary, adjust the oculars to the width of your eyes.
5. Turn the variable zoom knob to its highest magnification.
6. Cover the left ocular.
7. Keeping both eyes open, use the focus knob to focus your right eye on
Kevin Schumacher/GIA
the edges of the iris diaphragm. Obtain the sharpest possible image.
It’s important to carefully adjust the
microscope to your eyes.
8. Turn the variable zoom knob to its lowest magnification.
9. Cover the right ocular.
10. Keeping both eyes open, use only the fine-focus adjustment ring
located on the left ocular to focus your left eye on the iris diaphragm.
• Do not adjust the focus knob at this time. It is not used for
focusing the left ocular.
• The ocular might rise out of position as you turn the fine-focus
adjustment ring. Press down lightly on the ocular to keep it in
position while turning the ring.
• It is impossible to obtain a clear focus if the ocular is raised.
11. Check the focus with both eyes together at low, medium, and high
magnification. If the focus does not look right to you, refocus the
scope by repeating the sequence, starting from the beginning.

Fine focus adjustment ring

NOTE:
Once you have focused the microscope to your eyes, do not move the
fine-focus adjustment ring during grading.
If you accidentally turn the fine-focus adjustment ring, you will need to re-
focus your microscope, starting at the beginning of the sequence.

Kevin Schumacher/GIA

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DIAMOND GRADING LAB MANUAL

Types of Lighting
You will use different types of microscope illumination during the grading process.
These include darkfield, brightfield, reflected light and, sometimes, diffused lighting.
You will most often use darkfield illumination.

Darkfield Illumination
The diamond is illuminated from the side. Inclusions stand
out as bright objects against a black background. To achieve
darkfield illumination, keep the baffle closed and the iris
diaphragm open, and turn the well light up all the way for
maximum brightness. Looking through the pavilion with the
diamond held table-to-culet, this illumination allows you to
observe the majority of inclusions in the diamond.

Brightfield Illumination
The diamond is illuminated directly from beneath. Inclusions
stand out as dark objects against a bright background. To
achieve brightfield illumination, use the same lighting condi-
tions as with darkfield and simply tilt the diamond until light
reflects off the opposing facet’s surface, creating a bright
background. Some inclusions, such as brown internal
graining, are best seen in brightfield illumination.

Reflected Light
Reflected light allows you to view a facet surface while
preventing any view of the diamond’s interior. You can
achieve reflected light with an overhead light source. You
can also tilt the diamond in the well to reflect the well light
off a facet surface.

Diffused Illumination
Diffused illumination offers softened or scattered light,
which is especially helpful for detecting surface coatings
on a diamond or looking for signs of laser drilling. To achieve
diffused illumination, place a diffuser plate (or white tissue)
over the well.

16
 DIAMOND GRADING LAB MANUAL

LOUPE
In the GIA Diamond Grading System™, the final clarity, polish, and
symmetry grades are based on the diamond’s appearance in a fully corrected
10X triplet loupe.
In order to achieve accurate and consistent grading results, it is important
for your loupe to be well maintained. Be sure to clean it periodically with
lens cleaner and paper.
Denise Conrad/GIA
The cover of the GIA 10X loupe unfolds
to act as a handle.
Louping Environment
The standard louping environment consists of:
• A daylight-equivalent fluorescent overhead light source with a
translucent diffuser
• A non-reflective, darkened background
You can use the overhead light that’s attached to a standard gemological
microscope to create an ideal louping environment.
• Position the light with its diffuser cover parallel to the desktop and
use the base or the electrical housing to provide a black back-
ground. A dark material, such as black velvet, can be attached to the
back edge of the light source.
• It is important to remember that the light source takes about five
minutes to warm up and reach the proper intensity for louping.
When you do not have access to a microscope, use what you have and do
your best to replicate this environment.

Denise Conrad/GIA
The correct louping set-up includes daylight-equivalent lighting and a dark, non-reflec-
tive background.

17
DIAMOND GRADING LAB MANUAL

2 How to Loupe
To loupe a diamond girdle-to-girdle:
1. Clean the diamond thoroughly using a gemcloth.
2. Place your index finger through the loupe’s metal cover. Place your
thumb and middle finger on either side.
3. With the other hand, use your tweezers to pick up the diamond
girdle-to-girdle, using a hard-surface pick-up.
3 A little less than half of the diamond should extend beyond the end
of the tweezers.
4. Place the tweezers between the middle and ring fingers of your
loupe hand.
5. Rest the thumb of your loupe hand against a cheek as you examine
the diamond through the loupe. Keep both eyes open.
6. Hold the loupe 1 inch (2.54 cm) from your eye and 1 inch from the
diamond. This is the focal distance for a 10X lens. The diamond
should be about one-half inch (1.27 cm) below the overhead light
4 source.
• The eye, hand, and loupe connection cannot stand alone. It
needs a good base. Placing both elbows on the desk or on your
knees, or holding them close to your body, gives the necessary
support.
• Hold the table of the diamond approximately perpendicular to
the overhead light. Holding the diamond at any other angle will
allow the overhead light to reflect off the surface of the
diamond, masking the interior view.
5
• By keeping the lens stationary while finely adjusting the
diamond’s distance from the lens, an experienced grader can
focus on different depths within the diamond.

All by Denise Conrad/GIA

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 DIAMOND GRADING LAB MANUAL

7. Depending on the characteristics you want to examine, hold the

diamond at the light’s edge, just outside the light’s edge, or directly
under the light.
• Placing the diamond at the edge of or just under the light is
acceptable for louping most characteristics. You can achieve
brighter illumination of the diamond and its inclusions by
holding the diamond directly under the light.
• Some characteristics are more readily louped using less illumi-
nation. Holding the diamond beyond the edge of the light is best
for identifying most graining (brown graining, for example).
Also, this lighting technique usually makes it easier to loupe
clouds.

Overhead light source Overhead light source Overhead light source

Edge Under Outside

All by Peter Johnston/GIA

You can hold the diamond at the edge of the light (left), under the light source (center), or just outside the light source (right),
depending on the characteristics you want to view.

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DIAMOND GRADING LAB MANUAL

To loupe a diamond table-to-culet:

When characteristics such as pinpoints and internal graining are not visible
face-up at 10X, you will have to loupe the characteristics through the pavilion
in a table-to-culet position.
To loupe the diamond in the table-to-culet position, you use the same
parameters as for louping in the girdle-to-girdle position, including the
viewing distances and lighting environment. The only difference is that you
hold the stoneholder or tweezers horizontally rather than vertically.

Both by Denise Conrad/GIA

To loupe a diamond table-to-culet, hold the stoneholder or tweezers horizontally (left). Use the same louping
environment (right) as for girdle-to-girdle louping.

20
 DIAMOND GRADING LAB MANUAL

POINTER PROBE
You use a pointer probe to rotate a diamond while holding it in the table-to-
culet position. Other uses are to remove foreign material, such as lint or dust,
from the diamond’s surface and to touch a characteristic to help determine
if and how it breaks the surface.

Denise Conrad/GIA
With the diamond in the table-to-culet position, you can use the pointer probe to
gently turn it in the tweezers.

Cautions:
• Be cautious when you touch the pointer probe to a diamond’s
surface. Careless probing of a surface-reaching inclusion can cause
further damage.
• Do not rub burned facets or bruted girdles with the probe. Dragging
the probe across a burned facet or a bruted girdle can leave
unsightly dark grayish lines that can affect the diamond’s color
grade.

Both by Mitchell Moore/GIA

Take care when you touch a pointer probe to a diamond’s surface. Metal from the
probe remained on the surfaces of both this burned facet (left) and this bruted
girdle (right).

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DIAMOND GRADING LAB MANUAL

WATER-GRADING TOOLS
While examining a diamond in the microscope, you can clean and manipulate
it with a special sponge dipped in a soap-and-water solution. While some
graders prefer this “water grading” method, others use a combination of
gemcloth and pointer probe to clean and manipulate the diamond during
grading.

Soap-and-water Solution
To make a soap-and-water solution:
1. Fill a small glass container about halfway with distilled, bottled
water. Don’t use tap water, as it can leave a film on the diamond.

Kevin Schumacher/GIA 2. Add a small amount of liquid detergent. A few drops are enough:
Some graders use a small amount of Too much detergent will result in excessive soap bubbles.
liquid detergent mixed with distilled
water to help with the diamond examina-
tion process.
Cleaning and Turning the Diamond
During grading, use the sponge to turn the diamond and wipe its surface
clean. Be sure to remove any excess water before applying your sponge to
the diamond. As the water dries, it can leave a residue on the surface, so it
is important to clean the diamond with a gemcloth before evaluating polish,
symmetry, or clarity grades.

Kevin Schumacher/GIA
A sponge dipped in a soap-and-water solution can help you clean and manipulate the
diamond as you examine it.

22
 DIAMOND GRADING LAB MANUAL

STONE PAPERS
In the trade, loose diamonds are usually stored in stone papers, also called
parcel papers. They are usually marked on the front with detailed information
about the diamonds inside—size, weight, cost, and so on. A stone paper
might enclose a single large gem or several small ones. The package is known
in the trade as a parcel.
Stone papers usually consist of two or three paper layers, folded together.
The innermost layer is a thin, translucent liner called a flute. The color of
the flute affects the apparent color of the diamonds it holds.
© Photolink Creative Group
After repeated folding and refolding, some creases can become worn, and Stone papers usually consist of two or
the contents might fall out. Be sure to replace papers as soon as they show three paper layers folded together. The
any signs of wear. color of the inner liner, called a flute, can
influence the apparent color of the
It’s important to know how to handle stone papers skillfully. These instructions diamond.
and illustrations show the proper sequences for unfolding and folding them.

Unfolding
Before unfolding a parcel paper, feel for the location of the stone. It’s helpful
to gently tap one edge of the paper to shift the contents into the center. If the
paper contains a large number of small stones, tap one edge to move them
to the side opposite the one you’re opening.

To unfold a stone paper:

1. Hold the paper in both hands, then slip your thumb under the top
flap and lift it up.

All by Peter Johnston/GIA

2. Fold the bottom flap down and carefully open one of the side flaps.
Be careful with parcels of small stones because a few might be
caught on the wrong side of the fold.

23
DIAMOND GRADING LAB MANUAL

3. Tilt the paper sideways and slightly away from you, toward the
unopened side flap. Slip a finger inside the unfolded flap and open
the pocket slightly. Hold the paper more level as you open the flap
on the other side.

4. Open the bottom crease toward you, exposing the diamonds. Be

careful not to flip the stones out.

Both by Peter Johnston/GIA

Folding
1. Place the stone or stones in the middle of the second fold from the
bottom.
2. Fold the bottom flap up at this crease.
3. Fold the sides toward the middle, making sure you don’t trap any
stones on the wrong side of the fold.
4. Fold the bottom up and the top down.
5. Feel the paper to be sure the diamonds are still inside.

24
CARAT WEIGHT AND SIZE 25
Carat Weight 25
Weighing Loose Diamonds 26
Device Set-up and Verification 26
Weighing Procedure 28
Carat Weight Rounding 30

CARAT WEIGHT
Measuring Diamonds 31

AND SIZE
Recording Measurements 31
Minimum and Maximum Diameter 32
Length and Width 32
Depth 32
Average Girdle Diameter 33
Measuring Devices 34
Optical Measuring Devices 34
Millimeter Gauges 35
CARAT WEIGHT AND SIZE
The diamond trade has its own rules and tools for weighing and measuring
diamonds, and accuracy is essential. This section will provide you with the
skills and information you need to determine and express a diamond’s weight
and dimensions.

CARAT WEIGHT
Diamonds are weighed in metric carats. One metric carat (ct.) is equal to
0.20 grams. One carat can be divided into 100 equal units called points (pt.).
For example, 0.47 carat would be described as “47 points.”

Diamond weights must be

extremely accurate, so gem
professionals use electronic
scales to weigh them.

Eric Welch/GIA

25
DIAMOND GRADING LAB MANUAL

Weighing Loose Diamonds

Diamonds are weighed on an electronic scale or balance. Scales are equally
useful for weighing individual stones and large parcels.
Diamond weights must be extremely accurate, so gem professionals use
electronic scales to weigh them.

Device Set-up and Verification

Electronic scales are very accurate. However, to remain accurate they require
routine calibration and maintenance and a controlled environment. Following
are some important points to consider during set-up and before weighing a
diamond, to be sure the device is working properly.

Locate the scale on a firm, vibration-free surface, away from drafts

and heat sources.
• Be sure the device is not located near windows, direct sunlight,
heating ducts, cooling fans, or passageways with constant foot traffic.
• Most scales have a draft shield—a sliding glass door that protects
the sensitive weighing mechanism from drafts.

Level the scale.

• Most scales have a leveling mechanism, which usually consists of
adjustable feet and a liquid-filled capsule with a gas bubble inside.
The bubble moves as you adjust the scale’s feet. When the bubble is
centered in the capsule, the scale is level.
• Be sure to verify that the balance stays level between uses.

Level Not level

Both by Eric Welch/GIA

26
 DIAMOND GRADING LAB MANUAL

Check the scale’s calibration.

• Most scales come with a calibration weight for this purpose. If a
scale is knocked or moved, you should level and calibrate it again
or it won’t weigh gems accurately.
• Some scales have an internal auto-calibration function that runs
periodically.
• It’s a good idea to have a scale serviced regularly—once a year is
usually enough—by an authorized service agent.

Keep the scale and the area around it clean.

• Dust in the environment can accumulate on the scale.
• To prevent dust from accumulating inside the scale, keep the draft
shield closed when the scale is not in use.
There are many makes and models of scales, each with its own operating,
calibration, and maintenance procedures. It is important to follow the manu-
facturer’s instructions that come with the device you’re using.

27
DIAMOND GRADING LAB MANUAL

Weighing Procedure
To weigh a loose diamond:
1. Set the scale to zero.
• If you use a removable weighing pan, make sure it’s on the scale
before you set it to zero so you don’t include the weight of the
pan in the diamond weight.
• Confirm that the scale is set to zero each time you use it.
2. Clean the diamond thoroughly using a gemcloth.
Dirt, oil, or grease can alter a diamond’s weight.
3. Place the diamond in the center of the weighing platform.
• Use tweezers to handle the diamond. Oils from your fingers can
affect the diamond’s weight.
• Many scales are not calibrated for off-center load balance.

1 2 3

Eric Welch/GIA Denise Conrad/GIA Eric Welch/GIA

28
 DIAMOND GRADING LAB MANUAL

4. Close the draft shield.

Eric Welch/GIA

5. Wait for the reading to stabilize.

Eric Welch/GIA

6. Take the scale’s diamond-weight reading and round it to hundredths

of a carat, following the rounding rule explained in the next section.

29
DIAMOND GRADING LAB MANUAL

Carat Weight Rounding

It’s industry practice to weigh diamonds to at least a thousandth of a carat
and then round to hundredths.
Regulatory agencies, such as the US Federal Trade Commission, sometimes
allow for simple rounding, where the weight is rounded up when the number
in the thousandths place is greater than or equal to 5. However, the diamond
industry follows a stricter rounding standard, set by the World Federation of
Diamond Bourses, to round up only if there is a 9 in the thousandths place.

CARAT WEIGHT ROUNDING R ULE

t
Weight Rounding Example

x.xx0 - x.xx8 Round down 0.998 ct. = 0.99 ct.

x.xx9 Round up 0.999 ct. = 1.00 ct.

Some in the trade use even greater precision when weighing diamonds. For
example, the GIA Laboratory weighs diamonds to hundred-thousandths of
a carat. In this case, the weight is first rounded to the thousandths place
following the simple rounding rule and then to hundredths following the
stricter rounding rule used in the trade.

Examples:
• 0.99849 ct. = 0.998 ct. = 0.99 ct.
• 0.99850 ct. = 0.999 ct. = 1.00 ct.

Kevin Schumacher/GIA

The GIA Laboratory and many gem professionals weigh diamonds to hundred-thou-
sandths of a carat, then round to hundredths.

30
 DIAMOND GRADING LAB MANUAL

MEASURING DIAMONDS
A diamond’s physical dimensions include its diameter or length and width,
and its depth. These basic measurements are used to identify a stone, analyze
proportions and cut quality, choose a proper size mounting, and estimate the
weight of a mounted stone.

Recording Measurements
Diamond measurements are usually recorded in a series. On round shapes,
measurements are listed as “minimum diameter – maximum diameter ×
depth.” (Read it as “minimum diameter to maximum diameter by depth.”)
Fancy-shape measurements are listed as “length × width × depth.”

Diameter Width

Length
Depth

Round Shape Measurements

Minimum Diameter – Maximum Diameter × Depth

Example:
6.50 – 6.55 × 3.92 mm

Fancy Shape Measurements

Length × Width × Depth

Example:
6.52 × 4.12 × 3.37 mm

31
DIAMOND GRADING LAB MANUAL

Minimum and Maximum Diameter

The diameter of a round diamond is the distance from one girdle edge to the
opposite girdle edge, straight through the center.

diameter
Because even well-cut round diamonds are never perfectly round, you should
measure the diameter in several places and then record the minimum
(smallest) and maximum (largest) measurements.

Example:
Measurements: 4.23, 4.24, 4.26, 4.24, 4.27, and 4.28 mm
Minimum diameter = 4.23 mm
Maximum diameter = 4.28 mm

Length and Width

On fancy shapes, length and width measurements are used instead of diameter.
Typically, length is the longest dimension from end to end and width is the
widest measurement at a right angle (90°) to the length. There’s further
explanation of fancy-shape measurements in the Grading Fancy Cuts section.

width width width

length length length

Depth
A diamond’s depth is the distance from the table facet to the culet.

depth

32
 DIAMOND GRADING LAB MANUAL

Average Girdle Diameter

The average girdle diameter (AGD) is used as a basis for calculating the
proportions that affect a round diamond’s cut grade. It’s also used to estimate
the weight of a mounted diamond and to help choose a proper size mounting.
To calculate AGD, add the minimum and maximum diameters together and
divide by two.

Average Girdle Diameter = Min. Diameter + Max. Diameter

2

Example:
A round diamond has a minimum diameter of 4.23 and a maximum diameter
of 4.28.
Average girdle diameter = 4.23 + 4.28 = 8.51
= 8.51 ÷ 2 = 4.255 mm
When you’re using AGD to calculate a diamond’s proportions, use the result
to the thousandths place. To state AGD more simply, or when using it to
select a mounting, use the result to the hundredths place, following simple
rounding rules.

33
DIAMOND GRADING LAB MANUAL

Measuring Devices
There are many different types of instruments available to help you determine
a diamond’s basic measurements. No matter which instrument or measuring
system you use, it’s a good idea to pause after recording the measurements to
take another look at the stone and make sure the figures make sense.

Optical Measuring Devices

An optical measuring device determines a diamond’s dimensions by
scanning it through a full 360° rotation and capturing images of the
diamond’s outline. There are many makes and models of this type of device
available.

Advantages:
• Provides the most comprehensive and accurate measurement results
for rounds and most fancy shapes.
• Quickly and accurately determines all measurements and propor-
tions needed when using GIA Facetware™ to determine the GIA
Cut Grade on round brilliant diamonds.

Limitation:
Eric Welch/GIA • Works only for loose stones with table facets. You’ll need to use
An optical measuring device scans a different measuring instruments for mounted stones and stones
diamond through a full 360° rotation to
accurately determine its dimensions.
without table facets, such as briolettes or beads.

Caution:
• To obtain accurate results, the device must be properly maintained and
calibrated, and the diamond must be clean. A tiny piece of dust or lint
on the diamond during use can result in inaccurate measurements.

34
 DIAMOND GRADING LAB MANUAL

Millimeter Gauges
Millimeter gauges are used to capture a diamond’s basic dimensions.
There are many different kinds of millimeter gauges, and they can have
dial or digital read-outs. The types vary in precision and accuracy.

Advantages:
• They are portable and less expensive.
• They can be used to measure loose and mounted stones of
any shape and cutting style.

Cautions:
• These devices come in contact with the diamond, so you
need to use them carefully to ensure that you do not damage
or chip the diamond. For example, the jaws on some
millimeter gauges are spring operated: If you let go, they will
snap shut and possibly damage the stone or the instrument,
or both.
• Over time, the measuring faces can become worn, affecting
the accuracy of the results. It is important to calibrate and/or
replace these devices regularly.

Caliper gauges (left) and millimeter gauges (right) are simple instruments that hold a diamond
while taking its measurements. They come with both dial and digital read-outs.

35
DIAMOND GRADING LAB MANUAL

Using a Millimeter Gauge:

To measure a loose diamond on a millimeter gauge, place the diamond
between the inner jaws.
Dial gauges show tenths of a millimeter and whole millimeters up to 10.
Each time the needle makes a full rotation, you have to add 10 millimeters
to the measurement shown. To get an accurate measurement, you have to
add the reading on the smaller dial to the one on the main dial. Otherwise,
you might record 5.20 mm when the measurement is actually 15.20 mm.
With a dial gauge, you also have to estimate measurements to hundredths.
Gauges with digital readouts can display measurements to hundredths, elim-
inating the need for estimation.

Peter Johnston/GIA
A millimeter gauge measures the dimensions of both loose and mounted diamonds.
To measure a loose diamond, place it between the gauge’s inner jaws.

36
CLARITY G RADING 37
Clarity Factors 37
Size 38
Number 38
Location (Position) 39
Relief 39
Nature 40
Identifying Clarity Characteristics 41
Internal Inclusions 42
Surface-reaching Inclusions 45
Blemishes 49
Callable vs. Non-callable Clarity Characteristics 54
Non-callable Internal Graining 54
Non-callable Extra Facets 55
Non-callable Naturals 55

CLARITY GRADING
Other Features 56
Distinguishing Internal from Surface Characteristics 57
Windows and Mirrors 57
Focus and Depth of Field 60
Reflected Light 61
Clarity Grading Procedure 62
GIA Clarity Grades 68
GIA Clarity Grade Descriptions and Examples 69
Flawless (FL) 69
Internally Flawless (IF) 69
Very Very Slightly Included (VVS1 and VVS2) 70
Very Slightly Included (VS1 and VS2) 71
Slightly Included (SI1 and SI2) 72
Included (I1, I2, and I3) 73
Special Case Guidelines 74
Reflections 74
Reflecting Surface Graining 74
Plotting 75
What to Plot 75
Plotting Objectives 75
General Guidelines 76
The Comments Section 77
How to Plot 77
Plotting Internal Inclusions 79
Plotting Surface-reaching Inclusions 80
Plotting Blemishes 81
Plotting Procedure 82
Clarity Status 84
Critical Weights 84
GIA Clarity Status Descriptions 84
Repolishing for Flawless 85
CLARITY G RADING
Clarity is a gemstone’s relative freedom from clarity characteristics, which
are classified as inclusions or blemishes. Clarity is graded on a relative scale
from Flawless to Included, based on the types of clarity characteristics
present and their overall visibility at 10X magnification.

The GIA clarity scale (far right) includes diamond clarity grades in a range from Flaw-
less—with no inclusions and no blemishes visible at 10X magnification (above left)—to
Included—with inclusions that are obvious at 10X (above right).

CLARITY FACTORS
Five factors determine the overall effect of characteristics on a clarity grade.
Most of them are related to how readily you can see the characteristics at
10X magnification. The five factors are:
• Size
• Number
• Location (position)
• Relief
• Nature
You will need to assess how all five factors relate to each other when
determining a clarity grade. The relative importance of each factor varies
from diamond to diamond. One factor sometimes makes more difference to
the clarity grade than others.

37
DIAMOND GRADING LAB MANUAL

Size
You must consider the size of the inclusion in relation to the size of the
diamond. When all other factors are equal, the larger the inclusion and the
more visible it is, the lower the diamond’s clarity grade.

Both of these diamonds have a single inclusion in the same location and with the
same relief. In the diamond on the right, the inclusion is larger, making it more visible
and lowering the clarity grade.

Number
When all other factors are equal, the more inclusions or reflections of
inclusions that are visible face-up at 10X, the greater their effect on the
clarity grade. Because a diamond’s facets act like mirrors, they sometimes
reflect inclusions multiple times. Even when a small inclusion is somewhat
easy to see, reflections make it more apparent. Keep in mind that grades are
established by how readily you can see the inclusions, not by an exact count
of how many there are.

Both of these diamonds have a single inclusion of similar size and relief. The inclusion
in the diamond on the right is reflected a number of times, making it more visible and
resulting in a lower clarity grade.

38
 DIAMOND GRADING LAB MANUAL

Location (Position)
Generally, it is easier to see inclusions that are directly under the table. When
all other factors are equal, the closer an inclusion is to the center of the table,
the greater its effect on the clarity grade.

Both of these diamonds have a single inclusion of similar size and relief. The inclusion
in the diamond on the right is located under the table, making it more visible and
resulting in a lower clarity grade.

Relief
Relief refers to the contrast between the inclusion and its host diamond.
Relief can vary from high (more apparent) to low (less apparent). Generally,
the more an inclusion differs in brightness, darkness, or color from its host
diamond, the more visible it is and the greater its impact on the clarity grade.

Each of these diamonds has a single inclusion of similar size and in a similar location.
The inclusion in the diamond on the right has much higher relief, making it more visible
and resulting in a lower clarity grade.

39
DIAMOND GRADING LAB MANUAL

Nature
Nature refers to the type of characteristic and its inherent effect on the
diamond. The nature of a characteristic can cause refinement of the clarity
grade in a higher or lower direction. For example:
• An optical irregularity in the crystal structure, called internal graining,
has far less impact on the diamond’s clarity grade than a physical
break in the diamond, or feather, of similar size and appearance.

Vincent Cracco/GIA

Optical irregularity—internal graining Physical break—feather

• A superficial break in a diamond often has less impact on clarity

than an internal inclusion of similar size and relief.

Superficial break—bruise Internal inclusion—crystal

• Generally, if the stone has significant durability problems, it doesn’t

survive the friction and pressure of the cutting process, so durability
rarely affects clarity. However, very deep feathers that extend from
the crown to the pavilion, or that penetrate about one-third of the
way or more into the diamond, pose durability concerns and can
lower the grade.

A very large, very deep feather poses a

durability concern for this diamond.

40
 DIAMOND GRADING LAB MANUAL

IDENTIFYING CLARITY CHARACTERISTICS

Before you determine a characteristic’s impact on clarity, you must identify
it. This section describes the types of characteristics present in a diamond,
their appearances, and ways to identify them.
Clarity characteristics are classified as inclusions and blemishes:
• Inclusions: Characteristics that are totally enclosed within the
Internal inclusion
diamond (internal inclusions) or that extend into the diamond from
its surface, with visible depth at 10X magnification (surface-
reaching inclusions).
• Blemishes: Characteristics that are confined to the diamond’s
surface and have no visible depth at 10X magnification.
You might see other features, such as inscriptions, at 10X magnification.
These are considered neither inclusions nor blemishes, and have no impact
on clarity. Surface-reaching inclusion

Blemish
All by Peter Johnston/GIA

41
DIAMOND GRADING LAB MANUAL

Internal Inclusions
Internal inclusions can become part of a diamond during its formation or
result from crystal distortion during growth. They might also be introduced
by lasers during treatment or the inscription process. The various types of
internal inclusions, including definitions and examples, are shown on the
following pages.
Crystal (Xtl)—A mineral crystal contained in a diamond.

Mitchell Moore/GIA Mitchell Moore/GIA John Koivula/GIA

Most included crystals are smaller diamond crystals, and usually appear white (left) or
transparent (center). They might also be crystals of other minerals, such as garnet or
peridot, that appear colored (right). A crystal can create stress, causing a fracture to
develop around it inside the diamond (right).

Needle (Ndl)—A thin, elongated crystal that looks like a tiny rod at 10X.

Mitchell Moore/GIA Vincent Cracco/GIA Gary Roskin

Needles are typically white or bright (left), and can occur singly or in groups (center).
They sometimes appear dark (right).

Pinpoint (Pp)—A minute crystal that looks like a tiny dot at 10X.

NOTE:
Crystals, needles, and pinpoints are
all mineral crystal inclusions. The
only difference is their appearance
face-up at 10X. If an inclusion is not
visible in the face-up view at 10X, its
appearance and identity are deter- Mitchell Moore/GIA Gary Roskin

mined through the pavilion at 10X. Pinpoints are usually white, but might appear dark. They can occur singly (left) or in
groups (right).

42
 DIAMOND GRADING LAB MANUAL

Cloud (Cld)—A cluster of minute pinpoint inclusions that form a milky or

hazy area when viewed at 10X.

All by Mitchell Moore/GIA

Clouds vary in size and density. Some clouds have distinct outlines (left), while others
are spread throughout the diamond (center). Clouds might mimic the diamond’s
crystal structure or follow its growth pattern, with planes at 90 degree intervals
around the diamond (right).

Twinning wisp (TW)—A series of pinpoints, clouds, and/or crystals that

form within a diamond’s twinned growth plane, where crystal orientation
changed during growth.

Mitchell Moore/GIA Mitchell Moore/GIA Vincent Cracco/GIA

Twinning wisps look flat and ribbon-like (left), and they usually radiate out from the
center of the diamond (center). They often show totally enclosed or surface-reaching
high-relief separations (right).

Internal graining (IG)—A visible irregularity in the diamond’s crystal

structure in the form of lines, bands, or angles. Internal graining affects
clarity when it is white, reflective, or colored, or when it affects the
diamond’s transparency at 10X under standard viewing positions.

Vincent Cracco/GIA Vincent Cracco/GIA

Internal graining can appear as a reflective plane (left) or as whitish (center) or
colored (right) lines, bands, or areas. Most internal graining appears and disappears
as the diamond is rocked or turned.

43
DIAMOND GRADING LAB MANUAL

Grain center (GC)—A type of internal graining that consists of a small,

concentrated area of crystal distortion. It only affects clarity when it appears
white or bright at 10X.

Mitchell Moore/GIA Vincent Cracco/GIA Vincent Cracco/GIA

Grain centers can be pinpoint-like (left) or thread-like (center). They can occur alone
(left) or in groups (center and right).

Internal laser drilling (ILD)—A diamond treatment that utilizes a laser to

create a surface reaching feather or to expand a pre-existing feather around
a dark inclusion. It allows the use of chemicals to bleach the inclusion and
improve the diamond’s appearance. The drilling itself does not reach the
surface.

Vincent Cracco/GIA Shane McClure/GIA Shane McClure/GIA

Internal laser drilling typically results in irregular channels that are white (left), gray
(center), or black (right). The associated fracture is usually transparent, and connects
the inclusion being treated to the diamond’s surface.

Internal inscription—An identifying mark consisting of text, numbers,

symbols, or graphics rendered by laser and totally enclosed within a
diamond.

Both by Vincent Cracco/GIA

Internal inscription might be used to identify or brand a diamond.

44
 DIAMOND GRADING LAB MANUAL

Surface-reaching Inclusions
Surface-reaching inclusions are often the result of damage that occurs during
diamond formation, mining, or manufacturing, or after the diamond has been
fashioned. They might also be introduced by lasers during treatment, manu-
facturing, or inscription.
The following pages show the various types of surface-reaching inclusions,
including definitions and examples.
Feather (Ftr)—A general trade term that describes a break in a diamond.
Most breaks occur on a cleavage plane, a structural weakness in a direction
along one of the diamond’s four octahedral planes. A break in any other
crystal direction is a fracture.

All by Mitchell Moore/GIA

Feathers typically appear shiny or glossy (left), dull and white (center), or transparent.
Some feathers catch the light and blink from transparent to bright when you rock the
stone. They sometimes appear dark. Feathers, which occur in cleavage directions, are
straight (right), while breaks in other directions might appear curved (right).

Bearded girdle (BG)—Minute or minor feathers that run perpendicular to

a bruted girdle and extend into the diamond at 10X.

John Koivula/GIA Mitchell Moore/GIA

A heavily bearded girdle can create the appearance of a white, fuzzy fringe around the
diamond (right). Feathers in the girdle might remain after the girdle is polished or
faceted (right).

NOTE:
On a GIA Report, a bearded girdle is referred to in more general terms as
feathers in the girdle.

45
DIAMOND GRADING LAB MANUAL

Bruise (Br)—A small area of impact characterized by tiny, root-like feathers

that extend into the diamond at 10X.

All by Mitchell Moore/GIA

A bruise looks like a white mark on a facet (left). It has a “cottony” appearance when
viewed through an opposing facet (center) due to the root-like feathers that extend
into the diamond. In reflected light, the opening of the bruise appears dark (right).
Bruises typically occur on facet junctions, but might be located anywhere.

Chip (Ch)—A shallow opening on the surface resulting from damage that
occurs after fashioning. Chips occur only on facet junctions, at the girdle
edge, or at the culet.

John Koivula/GIA Mitchell Moore/GIA Mitchell Moore/GIA

Chips vary in size from very small to very large. They typically have rounded outlines
with step-like breaks (left). Small chips often appear white (center). Chips might
appear somewhat angular when, for example, they occur on the corner of a fancy-
shaped diamond (right).

Cavity (Cav)—An opening on the diamond’s surface that occurs when part
of a feather breaks away or when a crystal drops out or is forced out, typically
during polishing.

All by Mitchell Moore/GIA

Evidence of a feather often remains after it breaks away (left). When a crystal is pulled
out, the cavity resembles the original shape of the crystal (center). The opening of a
cavity appears dark in reflected light (left and right).

46
 DIAMOND GRADING LAB MANUAL

Indented natural (IN)—A portion of the rough’s original surface, or skin,

that dips below the polished diamond’s surface, with depth visible at 10X.

Vincent Cracco/GIA Vincent Cracco/GIA Mitchell Moore/GIA

Indented naturals show smooth, irregular growth markings such as trigons (left) or
parallel grooves (center). They usually occur at the girdle edge (left and right), but
might be located anywhere (center).

Knot (K)—An included diamond crystal that extends to the surface after
fashioning.

Mitchell Moore/GIA Vincent Cracco/GIA Vincent Cracco/GIA

Knots can be transparent (left), bright (center), or white. In reflected light, the outline
appears dark where the knot breaks the surface (right). Most colored crystals are
non-diamond mineral inclusions, so a dark or colored crystal that reaches a polished
diamond’s surface is classified as a crystal rather than a knot.

Etch Channel (EC)—An angular opening that starts at the surface and
extends into the diamond. It’s thought to be the result of high-temperature
igneous fluids that etched out a weak area in the diamond.

Vincent Cracco/GIA Mitchell Moore/GIA Mitchell Moore/GIA

Etch channels can vary in width and depth. They often look like long, narrow tubes
that taper inward and are striated in directions perpendicular to the length (left). They
often change direction (center), but might be straight (right).

47
DIAMOND GRADING LAB MANUAL

Patch of color (Patch)—A naturally occurring radiation stain left on a

polished diamond. It is considered a surface-reaching inclusion when it has
depth visible at 10X. When there is no 10X-visible depth, it is considered a
blemish.

Mitchell Moore/GIA Robert Kane/GIA

Radiation stains are originally green (left), but often turn brown from the heat of the
cutting process (center and right). They are usually found on a natural surface of a
polished diamond’s girdle edge (center and right), but they might appear on the plane
of a feather (left).

Laser drill-hole (LDH)—The result of a diamond treatment that utilizes a

laser to create access to a dark mineral inclusion. It allows the use of
chemicals to bleach the inclusion and improve its appearance. The drill-hole
starts at an internal inclusion and exits through the diamond’s surface.

Vincent Cracco/GIA Shane McClure/GIA Vincent Cracco/GIA

A drill-hole typically appears as a straight, hollow tube (left) with a tiny circular
opening at the surface. It might taper inward (center) or, on rare occasions, change
direction (right).

Indented inscription—An identifying mark that’s rendered by a laser and

consists of text, numbers, symbols, or graphics. It penetrates into the
diamond, and its depth is visible at 10X.

A poorly rendered laser inscription like

this one can penetrate into the diamond
when viewed at 10X.

48
 DIAMOND GRADING LAB MANUAL

Blemishes
Blemishes can be caused by conditions during setting or wear, introduced
in the cutting process, or result from the diamond’s crystal structure. They
might also be introduced by lasers used during manufacturing or marking.
The following pages show the various types of blemishes, including
definitions and examples.
Pit (Pit)—A minute opening that looks like a tiny white dot at 10X.

Mitchell Moore/GIA
A pit and a pinpoint both appear as a
tiny white dot at 10X. A pit, however, is
confined to the surface while a pinpoint
is internal.

Nick (Nck)—A small notch on a facet junction, usually along the girdle
edge or at the culet.

Nicks Chips

Both by Mitchell Moore/GIA

Nicks usually appear white and rounded (left and right). The only difference between
a nick and a chip is that a nick shows no depth at 10X (right).

Scratch (Scr)—A thin, dull, white line across the surface that shows no
apparent depth at 10X.

Vincent Cracco/GIA Mitchell Moore/GIA

Scratches might be straight (left) or curved (right). Curved scratches often appear
around the table (right).

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DIAMOND GRADING LAB MANUAL

Abrasion (Abr)—A series of minute scratches or pits along a facet junction,

producing a white or fuzzy appearance.

Mitchell Moore/GIA Mitchell Moore/GIA

Abrasion produces a fuzzy white line rather than a clear, sharp facet junction (left and
center). A diamond that’s very worn might show many abrasions, chips, and bruises
(right).

Polish lines (PL)—Fine parallel grooves on a facet surface, left by the

polishing process.

All by Mitchell Moore/GIA

Polish lines might appear white (Wht) (left) or transparent (TP) (center) and vary from
faint to heavy. Polish lines are best seen through an opposing facet. Polish lines within
a facet run parallel to each other and do not cross facet junctions. Heavy, transparent
polish lines that extend from a surface-reaching inclusion are referred to more specifi-
cally as drag lines (right).

Lizard skin (LS)—Wavy or bumpy area with a transparent, pitted texture,

resulting from polishing almost parallel to the cleavage plane.

Mitchell Moore/GIA Vincent Cracco/GIA Mitchell Moore/GIA

Lizard skin appears transparent (left) and is best viewed through an opposing facet
(center). The pitted texture is apparent in reflected light (right).

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 DIAMOND GRADING LAB MANUAL

Burn (Brn)—Whitish haze across a facet, or within a concentrated area,

caused by exposure to excessive heat during polishing, or occasionally from
a jeweler’s torch.

All by Mitchell Moore/GIA

Burn can be obvious (left) to faint (center). It is best seen by looking through an
opposing facet. Burn caused by a jeweler’s torch has a bubbly or melted appearance
(right).

Dop burn (Dop)—A surface burn resulting from excessive heat at the
location where a mechanical dop (a device used to hold the diamond during
cutting) touches the diamond.

Both by Mitchell Moore/GIA

A dop burn typically appears white, raised, and concentrated in a specific area, as
seen in these examples. It might also appear transparent.

Natural (N)—A portion of the rough’s original surface, or skin, left on a

polished diamond. Naturals affect clarity except when they are confined to
the girdle, don’t touch the crown or pavilion, and don’t thicken the girdle or
distort its outline.

All by Mitchell Moore/GIA

Naturals show smooth, irregular growth marks. The trigon (left) is a common growth
mark. Naturals can be located along any facet junction, but are usually located at the
girdle edge (left and center) or on the girdle (right). You might see a pair of naturals
located on directly opposing sides of the stone, or as four naturals in opposing pairs.

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DIAMOND GRADING LAB MANUAL

Extra facet (EF)—A facet that’s not required by the cutting style and placed
without regard for the diamond’s symmetry. An extra facet only affects
clarity when it is visible face-up at 10X.

Both by Mitchell Moore/GIA

Extra facets are usually located at the girdle edge, but might be placed anywhere on
the diamond. Extra facets have distinct, straight facet junctions. An extra facet’s
polishing direction is different from that of bordering facets.

Polish mark—A surface feature that resembles an extra facet without a

distinct or straight facet junction.

Vincent Cracco/GIA Mitchell Moore/GIA

Unlike an extra facet, there is very little difference in angle between a polish mark and
its bordering facet, so there is no distinct facet junction. Also, polish lines often run in
the same direction (left). Polish marks on the table might resemble naturals (right).

Rough girdle (RG)—Irregular pitted or granular surface of a bruted girdle,

caused by pits and nicks.

A rough girdle consists of pits and nicks that give it

a pitted or granular surface.

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 DIAMOND GRADING LAB MANUAL

Surface graining (SG)—An indication of irregularities in a diamond’s

crystal structure that appears on the polished diamond’s surface.

All by Vincent Cracco/GIA

Surface graining can appear as a straight or irregular line that is transparent or white.
Multiple surface grain lines often run parallel to each other (left). Surface graining
might cross a facet junction (left) or change direction within a single facet (center). It
is often seen where reflective internal graining or a twinned plane reaches the surface
(right).

Laser manufacturing remnant (LMR)—A characteristic that’s created

during a laser manufacturing stage—usually marking or sawing—and
remains on or within the polished diamond.

All by Vincent Cracco/GIA

When an LMR is confined to the surface at 10X, the remnant is considered a blemish
(left). If the remnant has depth that’s visible at 10X, it is considered a surface-
reaching inclusion (center). Sometimes, the laser penetrates into the diamond, leaving
an internal remnant and creating a stress fracture, or feather, which is considered an
inclusion (right).

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DIAMOND GRADING LAB MANUAL

Callable vs. Non-callable Clarity Characteristics

For grading purposes, clarity characteristics are defined as either callable or
non-callable:
• Callable: Characteristics that affect clarity. These are visible at
10X magnification.
• Non-callable: Characteristics that do not affect clarity and can
therefore exist on a Flawless diamond. These include inclusions
and blemishes that are visible only at a magnification higher than
10X, also referred to as “+10X.” Depending on their appearance or
viewing position, internal graining, extra facets, and naturals might
also be considered non-callable even when they are visible at 10X.

This diamond has a pinpoint that is visible under higher magnification (left), but no
longer visible at 10X (right). It is considered non-callable or +10X.

Non-callable Internal Graining

Internal graining is considered non-callable when it is transparent, fades
from view with little movement, or is visible only at an extreme angle to a
facet.

Shane McClure/GIA Gary Roskin Shane McClure/GIA

Transparent internal graining is commonly seen as lines, angles, and bands. It often
appears in a square or rectangular pattern (left) due to octahedral growth zoning. It’s
often seen as straight lines at 90-degree intervals across the crown facets (center).
Transparent internal graining might also display a swirled pattern (right).

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 DIAMOND GRADING LAB MANUAL

Non-callable Extra Facets

An extra facet that is not visible at 10X in the face-up position when you
look perpendicular to the crown is considered non-callable.

Both by Mitchell Moore/GIA

This diamond has an extra facet located on the pavilion (left). It is not visible face-up at
10X (right), so it is non-callable.

Non-callable Naturals
A natural is considered non-callable when it is confined entirely to the width
of the girdle and does not touch the crown or pavilion or thicken the girdle
or distort its outline.

Mitchell Moore/GIA
This diamond’s natural is confined entirely to its
girdle. The natural doesn’t thicken the girdle or
distort its outline, so it is considered non-callable.

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DIAMOND GRADING LAB MANUAL

Other Features
A diamond can have inscriptions and other features visible at 10X magni-
fication. They are considered neither inclusions nor blemishes and have no
impact on clarity.
These other features are described below, along with definitions and examples.
Inscription (Ins)—A mark made on the diamond that consists of text,
numbers, symbols, or graphics. Inscriptions are typically rendered with a
laser, but other methods are possible. An inscription confined to the surface
when observed at 10X has no effect on clarity.

Both by Mitchell Moore/GIA

Inscriptions are commonly placed on the girdle (left), but they can be located on any
facet (right).

Mounting feature—A feature added to facilitate the mounting of a

diamond.

Robert Weldon/GIA John Koivula/GIA

Mounting features include drill-holes on briolettes (left) and beads, and linear surface
grooves used to set a diamond in an “invisible” mounting (right).

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 DIAMOND GRADING LAB MANUAL

Distinguishing Internal from Surface

Characteristics
When a characteristic lies deep within the diamond, its appearance and
focus, and your perception of its depth, can make it easy to identify. However,
when a characteristic lies close to or on a facet surface, you must examine
it in more than one position, under higher magnification, or with different
lighting in order to determine its depth within the diamond.
There are three microscope observation methods that can help you determine
if a characteristic is an internal inclusion, a surface-reaching inclusion, or a
blemish:
• Windows and mirrors
• Focus and depth of field
• Reflected light

Windows and Mirrors

Each of a diamond’s facets acts as a “window” that you can look through to
see its interior. When you look through a “window,” the facet on the opposite
side acts as a “mirror.”

When you look

Windows through the crown,
the pavilion’s facets
act as mirrors.

Mirrors

When you look

Windows
through the
pavilion, the
crown’s facets
act as mirrors.

Mirrors

You will often see reflections of clarity characteristics in the “mirror” facets.
The reflections will appear within a single facet. You might also see prism
images of a characteristic through multiple “window” facets. Prism images
appear across facet junctions. You can use mirror reflections and prism
images to determine if the characteristic is an inclusion or a blemish.

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DIAMOND GRADING LAB MANUAL

To identify a characteristic that is close to a surface:

1. Turn the diamond over and look for the characteristic through an
opposing facet.
• If the characteristic is close to the crown, look for it through the
pavilion.
• If the characteristic is close to the pavilion, look for it through
the crown.
2. Determine if a mirror reflection is visible. If you see the character-
istic but there is no mirror reflection, it is a blemish. If you see a
mirror reflection, it is an inclusion. The distance between the inclu-
sion and its reflection tells you if it is totally enclosed or if it breaks
the surface.
• When there is some distance between the inclusion and its
reflection, it is totally enclosed. The closer the inclusion is to its
reflection, the closer it is to the surface.
• If the characteristic and its reflection are touching, the characteristic
is breaking the surface. The distance between the surface break and
the farthest point of the inclusion gives you an idea of its depth.

Internal Inclusion Surface-reaching Inclusion Blemish

Example: Example: Example:

• Characteristic is close to or on • Characteristic is close to or on • Characteristic is close to or on
the pavilion the crown the crown
• Looking through the crown, a • Looking through the pavilion, a • Looking through the pavilion, no
mirror reflection is visible mirror reflection is visible mirror reflection is visible
• There is distance between the • The characteristic and its • It is a blemish
characteristic and its reflection reflection are touching
• It is a totally internal inclusion • It is a surface-reaching inclusion

58
 DIAMOND GRADING LAB MANUAL

3. If a characteristic’s location makes it impossible to see through an

opposing facet, look for prism images that might identify it.
• Slowly turn the diamond as you look at the characteristic
through a nearby facet.
• If the characteristic moves across the facet junction and you see
prism images, it is totally internal.

This characteristic lies close to the crown and the girdle. It appears in prism images
across the crown, girdle, and pavilion, proving it is an internal inclusion.

NOTE:
All characteristics—inclusions and blemishes—can show prism images. The
presence of prism images proves that an inclusion is totally internal only when
the characteristic lies just beneath the facet you are looking through.

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DIAMOND GRADING LAB MANUAL

Focus and Depth of Field

As you focus on a point, anything within a certain distance above and below
that point will be clear and sharp. That distance is called the depth of field.
As you increase magnification, the depth of field gets shallower.
If you find it impossible to prove a characteristic’s identity by locating a
mirror reflection or prism image, high magnification—to decrease the depth
of field—along with the microscope’s focus knob, can help you determine
its identity.

To identify a characteristic that is close to a surface:

1. Increase the magnification to a high power.
2. Focus on the characteristic.
• If the characteristic is in focus and the surface is out of focus,
then it is internal.
• If the characteristic and the surface are in focus at the same
time, this method won’t prove its identity. It could be a surface-
reaching inclusion, a blemish, or an internal inclusion that is so
close to the surface that the focus level will not distinguish
internal versus surface.

1 2

Denise Conrad/GIA

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 DIAMOND GRADING LAB MANUAL

Reflected Light
You can also use reflected light to see where and how characteristics break
the surface. Surface-reaching inclusions typically appear black where they
break the surface. Blemishes will also be visible in reflected light.
Reflected light is helpful when a mirror reflection does not give enough
information to identify a characteristic. For example, you might know from
observing the reflection that a characteristic breaks the surface, but you can’t
tell how it breaks. You can also use reflected light when a characteristic is
close to or on the surface and a mirror reflection or prism image is not visible.

To create reflected light using the well light:

1. Make sure the well light is turned on at maximum brightness and
the baffle is closed.
2. Position the diamond at an angle where the well light reflects off
the facet surface.

1 2

Denise Conrad/GIA Mitchell Moore/GIA

To create reflected light using an overhead light source:

1. Turn off the well light and point the
overhead light source in a direction 1 2
perpendicular to the diamond’s surface.
• You can use the microscope’s over-
head light or another external light
source.
2. Position the diamond at an angle so the
light reflects off the facet surface.
• Only one facet at a time should be in
reflected light. If it is not, internal
inclusions would still be visible and
would resemble the dark appearance
of surface-reaching inclusions in re-
flected light. Denise Conrad/GIA Mitchell Moore/GIA

• You might find it easier to look through only one eye when
setting up reflected light.
• Very fine surface breaks might not be visible in reflected light.

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DIAMOND GRADING LAB MANUAL

CLARITY GRADING PROCEDURE

Final determination of a clarity grade is based on the diamond’s appearance
in a 10X loupe. Diamonds with larger inclusions or a hazy appearance are
also viewed with the unaided eye to check for eye-visibility. In order to
achieve accurate and consistent grading results, it is necessary to use:
• Controlled lighting conditions.
• Standard viewing angles and distances.
• A systematic grading method to be sure you examine every part of
the diamond and locate all characteristics that might affect clarity.
Many in the trade use a microscope to locate and identify characteristics and
to make the grading process more efficient. Also, increased magnification
is sometimes needed to properly identify and document a characteristic.

Suchada Kittayachaiwattana/GIA
GIA Laboratory graders use a microscope to locate and identify clarity characteristics (left).
However, all final grading decisions are based on the diamond’s appearance in a 10X loupe
(right).

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 DIAMOND GRADING LAB MANUAL

To determine a diamond’s clarity:

1. Clean the diamond thoroughly with a gemcloth.
2. Hold the diamond girdle-to-girdle in tweezers. Examine the
diamond face-up under 10X magnification with darkfield illumina-
tion to obtain an initial impression of the clarity (higher clarity
versus included).
• This initial impression can influence how you proceed with your
examination. For example, a higher-clarity diamond would
require a more careful examination.
• When inclusions are visible face-up, it is a good idea to assign a
general description of minor, noticeable, or obvious at this
point. Your initial impression is often correct when the grade-
setting characteristics are visible face-up.
3. Hold the diamond table-to-culet, with the pavilion in an upright
position, and rotate the diamond once to familiarize yourself with
the types of characteristics present. Consider how they might affect
your examination.
• Throughout the grading process, you can use a pointer probe or
a sponge and a soap-and-water solution to turn the diamond and
remove surface dust.
• As you search for characteristics, select a magnification that
allows the greatest field of view. Using magnification that is too
high or too low for the size of the diamond can make it difficult
to locate all of its characteristics. The average 1.00 carat
diamond is normally examined around 25X magnification, while
smaller diamonds should not be examined above 30X.

1 2 3

All by Denise Conrad/GIA

NOTE:
You can use a stoneholder or tweezers to hold the diamond table-to-culet. It
helps to hold the diamond in your non-writing hand so you can document char-
acteristics as needed.

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DIAMOND GRADING LAB MANUAL

4. To examine a round brilliant, divide the diamond into eight sections

and examine them one at a time. Each wedge-shaped section
consists of a bezel and a pavilion main with their bordering half
facets.
Marker 5. Select a reference point, or marker characteristic, to designate the
characteristic first section. This will help you keep track of the sections you have
examined. If you are plotting, it helps you orient the diagram to the
diamond.
• Choose a unique characteristic that is easy to locate and identify.
• If possible, choose an inclusion that is visible face-up and not in
the center of the diamond.
Marker
1 characteristic • If the diamond is inscribed, you can use its inscription to desig-
2 8 nate the first section.

3 7

4 6
5

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 DIAMOND GRADING LAB MANUAL

6. Thoroughly examine each section, one at a time. First, examine the

pavilion, then the girdle, and then the crown (see illustrations and
explanations below).
• As you look for characteristics, gently rock the diamond and
slowly turn it back and forth to get the best possible contrast
between characteristic and background. Also, rock the diamond
between brightfield and darkfield illumination. Some character-
istics are more visible when viewed at different angles or in
brightfield illumination.
• Focus in and out of the diamond as you move the diamond
slightly up and down or, if needed, use the focus knob.
• Identify and, if applicable, plot clarity characteristics as you
come across them.
• Use as much magnification as you need to properly identify a
characteristic, but remember that all final grading decisions are
made at 10X.

PAVILION, G IRDLE, AND CROWN EXAMINATION

Pavilion Examine the pavilion surface and the

interior space behind it, through the
central depths of the diamond to the
crown surface. Be sure to include the
areas near the culet and all the way to
the girdle.
This is referred to as the 6 o’clock
position.
6 o’clock

Girdle Slowly turn the diamond to the profile

view. Examine the entire girdle area,
including the areas right above and
below the girdle.

Crown 12 o’clock Slowly turn the diamond to the face-up

view. Examine the crown surface and
the interior space between the crown
and pavilion surfaces. Looking through
the bezel, turn the diamond to examine
its depths all the way to the culet.
This is referred to as the 12 o’clock
position.

65
DIAMOND GRADING LAB MANUAL

7. Rotate the diamond from one section to the next, performing the
same thorough pavilion, girdle, and crown examination procedure
with each turn.
• Always turn the diamond in a consistent direction (for example,
always to the right).
• Keep count of which section you are examining. If you lose
track, you can always return to your marker characteristic and
then count your way back.
• You know you have examined all eight sections when you return
to your marker characteristic.

3 7 4 8

2 8 3 1
1 2

8. Hold the diamond girdle-to-girdle in the tweezers.

• In the face-up view, examine the table and culet areas that were
previously covered by the tweezers or stoneholder. If applicable,
plot characteristics located in these areas.
• On higher-clarity diamonds, examine the culet area more closely
in profile view. Look for pinpoints or other minute inclusions.
Confine your search to the area nearest you. Examine the culet
area in four positions, each time setting the diamond down and
turning it a quarter turn.

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 DIAMOND GRADING LAB MANUAL

9. With the diamond in the face-up position, examine its clarity char-
acteristics with a 10X loupe to determine their overall visibility.
• Be sure to use a standard louping environment and procedures,
as described on pages 17 to 20.
• View the diamond face-up in at least four different positions.
Some characteristics might be more or less apparent when the
diamond is oriented differently.
• For grade-setting characteristics that are not visible face-up,
loupe the characteristic in the table-to-culet position.

9 x
x

x
Denise Conrad/GIA

10. For lower-clarity diamonds, or diamonds with a hazy appearance,

10
view the diamond face-up with your unaided eye at a distance of 16
to 18 inches (41 to 46 cm) under the overhead light source. You will
consider the eye-visibility of the characteristics when you deter-
mine the final clarity grade.
11. Assign a clarity grade of Flawless, Internally Flawless, VVS1,
VVS2, VS1, VS2, SI1, SI2, I1, I2, or I3.
• Consider all five clarity factors and overall face-up appearance,
as well as clarity characteristics seen in any view.
• Place the most emphasis on the diamond’s face-up appearance
with a 10X loupe.
• Use the clarity grade definitions and examples on the following
pages to help you determine the rating.
Denise Conrad/GIA

67
DIAMOND GRADING LAB MANUAL

GIA CLARITY GRADES

Clarity grades represent a range of visibility within which clarity characteristics,
when present, range from barely visible to obvious. The GIA clarity grading
scale provides universally understood terms for describing diamond clarity.

Overview of GIA Clarity Grades

This table lists each GIA clarity grade with a basic description of the overall visibility of characteristics
at 10X magnification. You’ll find more-detailed descriptions and examples on the following pages.

Clarity Grade Visibility of Characteristics at 10X Magnification

No inclusions and no blemishes visible at

FL Flawless
10X magnification.

No inclusions and only insignificant blemishes

IF Internally Flawless
visible at 10X magnification.

VVS 1
Minute inclusions that range from extremely
Very Very Slightly Included difficult (VVS ) to very difficult (VVS ) to see at
1 2

10X magnification.
VVS 2

VS 1
Minor inclusions that range from difficult (VS ) 1

Very Slightly Included to somewhat easy (VS ) to see at 10X

2

magnification.
VS 2

SI 1

Noticeable inclusions that are easy (SI ) or

Slightly Included 1

very easy (SI ) to see at 10X magnification.

2

SI 2

I1

I2 Included Obvious inclusions visible at 10X magnification.

I3

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 DIAMOND GRADING LAB MANUAL

GIA Clarity Grade Descriptions and Examples

Flawless (FL)
A Flawless diamond shows no inclusions and no blemishes when examined
under 10X magnification.
A diamond can have the following features, visible at 10X, and still qualify
for a Flawless grade:
• Naturals confined entirely to the girdle, as long as they don’t
thicken the girdle or distort its outline.
• Extra facets that are not visible face-up at 10X magnification.
• Non-callable internal graining.
• Inscriptions confined to the surface and that don’t appear to penetrate
the surface when viewed at 10X magnification.
• Mounting features.

Internally Flawless (IF)

An IF diamond shows no inclusions and only insignificant blemishes when
examined under 10X magnification. Blemishes that might set the IF grade
include:
• Polish features (pit, nick, scratch, abrasion, polish lines, burn, etc.).
• Naturals.
• Extra facets, visible face-up at 10X magnification.
• Surface graining that is not extensive or reflecting (see page 74).
• Patches of color that show no depth at 10X magnification.

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DIAMOND GRADING LAB MANUAL

Very Very Slightly Included (VVS1 and VVS2)

VVS diamonds contain minute inclusions that range from extremely
difficult (VVS1) to very difficult (VVS2) to see at 10X magnification. Typical
inclusions that might set the VVS grade include:
• Pinpoints, needles, clouds, or callable internal graining, visible only
through the pavilion at 10X (VVS1) or extremely difficult to see
face-up at 10X (VVS1).
• Pinpoints, needles, internal graining, or clouds that are very diffi-
cult to see face-up at 10X (VVS2).
• Minute surface-reaching inclusions (chip, cavity, feather, bruise,
bearding, indented natural, etc.).

Mitchell Moore/GIA Shane McClure/GIA

VVS1 Pinpoint VVS1 Internal graining

VVS2 Pinpoint VVS2 Feather

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 DIAMOND GRADING LAB MANUAL

Very Slightly Included (VS1 and VS2)

VS diamonds contain minor inclusions that range from difficult (VS1) to
somewhat easy (VS2) to see at 10X magnification. All inclusions are
possible; the grade depends on their overall visibility when you consider all
five clarity factors. Typical inclusions that might set the grade include small
crystals, knots, or distinct clouds, or minor surface-reaching inclusions such
as a feather, cavity, or indented natural.
In very rare cases, a VS stone might contain an eye-visible inclusion. You
need to consider its size, nature, location, number, and relief in relation to
the size and cut of the stone. For example, an emerald cut that weighs more
than 1 ct. can have an eye-visible crystal under the corner of the table and
still be in the VS range.

VS1 Crystal VS1 Feather

VS2 Crystal VS2 Feather

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DIAMOND GRADING LAB MANUAL

Slightly Included (SI1 and SI2)

SI diamonds contain noticeable inclusions that are easy (SI1) or very easy
(SI2) to see at 10X magnification. All inclusions are possible; the grade
depends on their overall visibility when you consider all five clarity factors.
Typical inclusions that might set the grade include crystals, feathers, clouds,
or twinning wisps.
A stone with an eye-visible inclusion can be graded SI, but in general the
characteristics in an SI1 diamond are not usually visible face-up without
magnification. You’ll see eye-visible inclusions more often in an SI2 stone.

SI1 Crystal SI1 Feather

SI2 Crystal SI2 Feather

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 DIAMOND GRADING LAB MANUAL

Included (I1, I2, and I3)

These diamonds contain obvious inclusions visible at 10X magnification.
One or more of the following is typical of these inclusions:
• They can be seen face-up without magnification.
• They seriously affect the stone’s durability.
• They’re so large or numerous that they affect transparency and
brightness.
The inclusions in I1 diamonds are usually quite visible to the unaided eye.
In I2, they’re easily visible. In I3, they’re extremely easy to see and might
affect the stone’s durability.

I1 Crystal with Feather I1 Feathers

I2 Crystals I2 Feathers

I3 Crystals and Feathers I3 Feathers

73
DIAMOND GRADING LAB MANUAL

Special Case Guidelines

There are some special circumstances that might arise during clarity grading.
You must be aware of them and know how to compensate for them.

Reflections
Reflections are only considered in the clarity grade when they are easily
visible face-up during routine louping, and are close to or on the same focal
plane as the physical inclusion(s). Reflections observed while focusing
beyond the culet or those seen only through the pavilion are not considered.

Reflecting Surface Graining

Surface graining is a blemish that, in most cases, qualifies the diamond for
an IF grade. In rare cases, extensive surface graining with obvious mirror
reflections seen face-up at 10X can lower the clarity further. Diamonds with
reflecting surface graining are often graded VS1 or lower.

The crystal in this diamond’s table is Viewed face-up at 10X, this diamond
reflected a number of times in the has extensive surface graining with
pavilion. The reflections affect the clarity obvious mirror reflections.
grade because they are easily visible
face-up at 10X.

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 DIAMOND GRADING LAB MANUAL

PLOTTING
A plot is a map of a diamond’s clarity characteristics. The plot itself matches
or closely resembles the diamond’s shape and facet arrangement, and
consists of a crown and a pavilion view. Symbols are used to represent the
type, location, relative size, and sometimes the shape of the characteristics
being plotted.

To support a diamond’s clarity grade, identify it, and document its condition (left),
clarity characteristics are plotted on a diagram. On a GIA Report, the diagram is
oriented with the crown view on the left and the pavilion view on the right (right).

What to Plot
While plotting every characteristic is one way to represent a diamond, this
task is time consuming and unnecessary. In the trade, the level of detail on
a plot varies, depending on its purpose—whether, for example, it’s part of
a laboratory report or an appraisal document.

Plotting Objectives
There are three main objectives for plotting a diamond:
• To support the clarity grade
• To identify a diamond
• To document a diamond’s condition at the time it is graded
It’s important to keep these objectives in mind when you decide what to plot.
Characteristics that are not plotted are often noted in the comments section
of the report or appraisal document, especially when they’re needed to
support the clarity grade or disclose a treatment.

NOTE:
Every diamond you grade in the classroom presents you with a good learning
opportunity. Therefore, as an educational aid, you will find that the classroom
keycards contain more characteristics than are necessary, or that would be
shown on a report.

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DIAMOND GRADING LAB MANUAL

General Guidelines
In the classroom, follow these general guidelines when deciding what
to plot or what to note in the comments section:
• Always plot the following:
Laser drill-hole
Crystal
Needle
Knot
Etch channel
Indented natural
Callable extra facet
Callable natural
• Plot clouds that are distinct. Note clouds that spread throughout the
diamond in the comments section.
• Plot enough twinning wisps to support the clarity grade and iden-
tify the diamond. Note any additional twinning wisps in the
comments section. Because twinned diamonds are typically heavily
included, there’s no need to plot every twinning wisp.
• It is not necessary to plot every pinpoint. Plot pinpoints only if they
set the grade or when they’re needed to help identify the diamond.
• In general, plot all feathers, bruises, chips, and cavities. If they’re
minute, only plot those needed to support the clarity grade.
• Always note the following characteristics in the comments section:
Internal laser drilling
Callable internal graining (including grain centers)
Patches of color
Indented and internal inscriptions
Surface graining
• Note a bearded girdle in the comments section when it’s needed to
support the diamond’s clarity grade or document its condition.
There’s no need to note a lightly bearded girdle that is not grade-
setting. On a GIA Report, a bearded girdle is described more
generally as “feathers in the girdle.”
• Do not plot polish features such as polish lines, burn, scratches, abra-
sions, and laser manufacturing remnants. These are accounted for
under the polish rating, and rarely impact clarity. On internally flaw-
NOTE: less diamonds, plot enough polish features to support the grade. On a
Do not plot non-callable clarity char- GIA Report, polish details, when present on IF diamonds, are noted in
acteristics. These might appear on the comments section to support the grade.
documents produced in the trade,
especially when needed to identify • Note a laser manufacturing remnant in the comments section only
FL or IF diamonds. when its depth can be observed at 10X and when it’s needed to
support the diamond's clarity grade or document its condition.

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 DIAMOND GRADING LAB MANUAL

The Comments Section

Use general statements when noting characteristics in the comments section.
For example:
• Internal graining is not shown.
• Additional clouds are not shown.
• Additional twinning wisps are not shown.
• Feathers in the girdle are not shown. Mitchell Moore/GIA
The clouds are spread throughout this
When a grade-setting clarity characteristic is not plotted, state its grade- diamond, so you would note them in the
setting status in the comments section. For example: comments section rather than plot them.

• Clarity grade is based on internal graining that is not shown.

• Clarity grade is based on clouds that are not shown.

How to Plot
Clarity characteristics are plotted in red, green, or black. Each category has
its own color:
• Red symbols indicate most inclusions.
• Red and green together indicate laser drill-holes, knots, cavities, in-
dented naturals, and etch channels.
• Green is used to indicate blemishes, except extra facets.
• Black indicates extra facets and, if the stone is mounted, the posi-
tion of metalwork.
When plotting, use fine-tipped ballpoint pens in appropriate colors. Try to
make the lines as fine as possible. For your reference, there’s a list of plotting
symbols and abbreviations on the next page.

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DIAMOND GRADING LAB MANUAL

PLOTTING SYMBOLS AND ABBREVIATIONS

Internal Inclusions Blemishes

Crystal (Xtl) Natural (N)

Needle (Ndl) Extra facet (EF)

Pinpoint (Pp) Surface graining (SG)

Cloud (Cld) Pit (Pit)

Twinning wisp (TW) Nick (Nck)

Internal graining (IG) Scratch (Scr)

Polish lines (PL)

Grain center (GC)
*
Burn (Brn, Dop)

Surface-reaching Inclusions Lizard skin (LS)

Laser drill-hole (LDH) Abrasion (Abr)

Knot (K) Rough girdle (RG)

Feather (Ftr) Polish mark

Bruise (Br) Laser manufacturing

remnant (LMR)
Chip (Ch)

Cavity (Cav) Other Features

Indented natural (IN) Inscription (Ins)

Etch channel (EC) Mounting feature

Bearded girdle (BG) Metalwork (Metal)

NOTE:
There are no plotting symbols for internal laser drilling, patch of color, or
laser manufacturing remnant inclusions. Symbols shown in the gray areas
are not plotted on a GIA Report but might be shown on the keycard used
in the classroom for educational purposes or on other diagrams
generated in the trade such as appraisal documents.

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 DIAMOND GRADING LAB MANUAL

Plotting Internal Inclusions

You plot internal inclusions in red where they are visible face-up at 10X.
Draw the symbol so it represents the approximate size and shape of the
inclusion as seen at 10X.
Here are some additional guidelines for plotting internal inclusions:
• If an internal inclusion is not visible face-up at 10X, plot it where it
is visible through the pavilion.
• Plot only the inclusion, not its mirror reflections.
• When prism images are visible face-up, plot the image of the inclu-
sion that appears closest to the center of the diamond when you
look perpendicular to the table.
• If a crystal with a stress fracture is totally enclosed, plot the entire
characteristic face-up as a single crystal. Otherwise, plot the crystal
where it is visible face-up and the stress fracture as a feather where
it breaks the surface.

This diamond has a totally enclosed single

crystal with a stress fracture that displays
mirror reflections and multiple prism
images (above). You would plot the entire
characteristic face-up as a single crystal
(right).

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DIAMOND GRADING LAB MANUAL

Plotting Surface-reaching Inclusions

You plot surface-reaching inclusions in red, or red and green, only where
they break the surface. Draw the symbol so it represents the approximate
size and shape of the break or opening as seen at 10X.
Here are some additional guidelines for plotting surface-reaching inclusions:
• If a surface-reaching inclusion breaks both crown and pavilion, plot
it where it breaks in both locations.
• If a surface-reaching inclusion breaks only in the girdle, plot it once,
either on the crown view (if its depth is visible face-up at 10X) or on
the pavilion view (if its depth is not visible face-up at 10X).
• When a laser manufacturing remnant penetrates the diamond and
creates a fracture, plot it as a feather where it breaks the surface. If
the fracture is totally enclosed within the diamond, plot it as a
crystal where it is visible face-up at 10X. There’s no need to note
the laser manufacturing remnant itself.

Both by Mitchell Moore/GIA

This diamond has a cavity and a feather
that break at both the crown and pavilion
(above). Plot each one where it breaks the
surface (right).

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 DIAMOND GRADING LAB MANUAL

Plotting Blemishes
Plot blemishes in green and extra facets in black, on the surface where they
are located. Draw the symbol so it represents the approximate size and shape
of the blemish as seen at 10X.
Here are some additional guidelines for plotting naturals located on the
girdle:
• Plot those confined to the girdle on the pavilion view.
• Plot those that reach the pavilion on the pavilion view.
• Plot those that reach the crown on the crown view.
• Plot those that reach both crown and pavilion on both views.

Mitchell Moore/GIA
This diamond has a natural on its pavilion
surface (above), so it is plotted in that
location on the diagram’s pavilion view
(right).

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DIAMOND GRADING LAB MANUAL

Plotting Procedure
While following the clarity-grading process described on pages 62 to 67, you
plot clarity characteristics as you come across them. When you plot a diamond,
you must coordinate the crown and pavilion orientations so you know how the
face-up view corresponds to the face-down view. The best way to align the
diamond to the plotting diagram is to use a numbering system.
To plot a diamond:
1. Select a diagram that matches or most closely resembles the shape
and cutting style of the diamond.
2. Plot the reference point, or marker characteristic, in the number-one
section.
3. During your table-to-culet examination, plot any necessary charac-
teristics as you come across them.
• Use the guidelines explained earlier to determine what and how
to plot.
• Although you might need higher magnification to locate and
identify characteristics, be sure to plot their relative size when
viewed at 10X magnification.
4. Count your way around the diamond from one section to the next.
Use the numbered sections, as shown below, to plot characteristics
in their appropriate locations.
• Remember to rotate the diamond in one direction only. To follow
the example shown in the illustrations below, always turn the
diamond to the right.
• When you plot characteristics, rotate the diagram so it aligns
with your current view of the diamond.
These illustrations show
Diamond Diagram the relationship of the
three orientations of a
1
2 8 1 round brilliant diamond
(left) to its crown and
2 8 pavilion plot diagrams
3 7
(right). Numbering the
3 7 sections from 1 to 8 can
4 6
5 help you understand and
4 6 follow an orderly plotting
5 procedure. Each section
consists of a bezel and a
pavilion main, along with
their bordering half
facets.
5
4 6
3 7 3 7
2 1 8 8
2
1

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 DIAMOND GRADING LAB MANUAL

5. Near the end of the clarity-grading process, examine the diamond

face-up and plot characteristics that are located in the table. Use
your number-one position as a reference point to ensure that char-
acteristics in the table are plotted in their proper locations.
6. After you have plotted all characteristics, create a Key to Symbols
with the appropriate ink colors and characteristic abbreviations. List
the characteristics in order of their importance to the clarity grade:
• Laser drill-holes, listed first as part of disclosure
• Grade-setting inclusions
• Other inclusions, in order of severity
• Naturals
• Extra facets

On a GIA Diamond Grading Report, clarity characteristics are represented on a

plotted diagram or in the comments section. A Key to Symbols identifies the
clarity characteristics shown on the plot. The symbols are listed in order of their
importance to the clarity grade.

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DIAMOND GRADING LAB MANUAL

CLARITY STATUS
A fashioned diamond can sometimes be recut or repolished to
remove or reduce grade-setting characteristics and obtain a higher
clarity grade. Whether or not a diamond’s clarity can be improved
is referred to as its clarity status. Its status depends on the depth
of the grade-setting characteristics, the presence of other charac-
teristics, and the weight of the diamond. Removing too much weight
can lower a diamond’s value, even while improving the clarity.

Critical Weights
Diamond per-carat prices increase at certain weights, called price
breaks. The weights where major price breaks occur are referred
to as critical weights. Critical weights include all whole-carat sizes
(1.00 ct., 2.00 cts., etc.), as well as 0.30 ct., 0.50 ct., 0.70 ct., and
1.50 cts.
There are also some other minor price breaks. Most in the trade
will not recut a diamond if doing so would result in the diamond
falling below a critical weight.

GIA Clarity Status Descriptions

The GIA Laboratory uses the following descriptions to indicate a
diamond’s clarity status:
• Not potential: Grade-setting inclusions cannot be re-
moved with minor recutting or minimal weight loss, or
doing so might result in the diamond falling below a criti-
cal weight.
Upon request, the GIA Laboratory will issue a sepa-
rate document to identify Potential and Improvable • Potential: Clarity might be improved to IF with minor re-
diamonds. It lists the clarity status along with a cutting and minimal weight loss.
plotted diagram. Characteristics that would need to
be removed or reduced in order to improve clarity • Not Potential/Improvable: Clarity might be improved to
are circled in blue. VVS1 or VVS2 with minor recutting and minimal weight
loss. There are internal inclusions present that would pre-
vent an Internally Flawless grade.
When deciding to recut a diamond, other factors are considered in
addition to clarity and weight. These include the impact that recutting
would have on the diamond’s proportions and symmetry. You should
always discuss recutting options with an experienced cutter.

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 DIAMOND GRADING LAB MANUAL

Repolishing for Flawless

Normally, blemishes on an IF diamond can be removed with minor
repolishing. Surface graining is an exception because it usually can’t be
polished away. It is important to note, however, that it is very difficult to
polish a diamond without leaving polishing features on its surface. Therefore,
most in the trade do not try to obtain a Flawless grade by repolishing an IF
diamond.
Upon request, the GIA Laboratory indicates the blemishes that must be
removed from an IF diamond to obtain a Flawless grade, and states the
diamond’s clarity status as “IF/Improvable.”

85
CUT G RADING 87
Cut Quality Factors 87
Visual Evaluation of Face-up Appearance 90
Viewing Environment 91
Evaluating Brightness 92
Evaluating Pattern 94
Evaluating Fire 98
Evaluating Proportions and Design 101
GIA Facetware® Cut Estimator 102
Accuracy, Precision, and Tolerance 102
Weight Ratio and Overweight Percentage 104
Effect on Cut Grade 105
Total Depth Percentage 106
Effect on Cut Grade 107
Table Percentage 108
Direct Measurement 108
Ratio Method 110
Bowing Method 112
Flash Method 114
Effect on Cut Grade 115
Star Length Percentage 116
Effect on Cut Grade 117
Crown Angle 118
Crown Angle Reference Card 118

CUT GRADING
Profile Method 120
Face-up Method 121
Effect on Cut Grade 122
Crown Height Percentage 123
Effect on Cut Grade 123
Culet Size 126
Special Case Guidelines for Culet Size 127
Effect on Cut Grade 128
Pavilion Depth Percentage and Pavilion Angle 129
Effect on Cut Grade 133
Lower Half Length Percentage 134
Effect on Cut Grade 135
Girdle Thickness Percentage 136
Effect on Cut Grade 137
Girdle Thickness Description 138
Special Case Guidelines for Girdle Thickness 139
Effect on Cut Grade 140
Girdle Condition 141
Girdle Thickness Variations 142
Painting 142
Digging Out 143
Visual Evaluation of Painting and Digging Out 144
Effect on Cut Grade 148
Combined Effect of Proportions 149
Table Percentage, Crown Angle, and Pavilion Angle 150
Evaluating Craftsmanship/Finish 158
Polish 158
Polish Features 158
Determining Polish 160
Effect on Cut Grade 162
Symmetry 163
Symmetry Variations 164
Determining Symmetry 170
Effect on Cut Grade 172
Estimating the Cut Grade 173
Optical Measuring Device with GIA Facetware® 173
Online GIA Facetware® Cut Estimator 174
Visual Estimation Techniques and Look-up Tables 175
CUT G RADING
The cut of a diamond can refer simply to its shape and its cutting style or
facet pattern. In diamond grading, cut also refers to a diamond’s overall cut
quality.
The GIA Cut Grading System is used to evaluate the cut quality of a standard
round brilliant diamond in all clarities across the D-to-Z color range. Cut is
graded on a relative scale from Excellent to Poor.
The standard round brilliant consists of 57 or 58 facets, fashioned with
modern proportions. Older style round brilliants, including the old European
brilliant and the circular brilliant, are not evaluated under modern cutting
standards and therefore do not receive a cut grade. You’ll find the quality
standards for these antique cutting styles in the Grading Fancy Cuts section
of this manual.

CUT QUALITY FACTORS

There are seven factors of cut quality that affect a diamond’s cut grade. The
first three—brightness, fire, and scintillation—relate to the diamond’s face-
up appearance. Weight ratio and durability relate to the diamond’s design.
Polish and symmetry relate to craftsmanship—the care that contributed to
its finish quality.

CUT QUALITY FACTORS

Face-Up Design
Appearance Weight Ratio • Durability

Brightness
Scintillation
Fire Craftsmanship
Polish • Symmetry

Your analysis of a diamond’s proportions and finish includes an evaluation

of each of these factors. In the GIA Cut Grading System, a diamond’s overall
cut grade is determined according to the lowest value assigned to any one
of these seven quality factors.

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DIAMOND GRADING LAB MANUAL

Brightness is the face-up effect of all the diamond’s internal and external
reflections of white light.

All by Eric Welch/GIA

Increased brightness Decreased brightness

Scintillation is a combination of sparkle and pattern.

• Sparkle consists of the spots of white or colored light that flash as
the diamond, the observer, or the light source moves.
• Pattern is the relative size, arrangement, and contrast of bright and
dark areas that result from a diamond’s internal and external reflec-
tions, seen face up.

Al Gilbertson and Maha Tannous/GIA Al Gilbertson and Barak Green/GIA Al Gilbertson and Barak Green/GIA

Pleasing pattern Distracting pattern

Fire is the appearance and extent of the flashes of color you see face-up in
a polished diamond.

All by Eric Welch/GIA

More fire Less fire

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 DIAMOND GRADING LAB MANUAL

Weight Ratio is the result of an analysis of the diamond’s weight in relation

to its average girdle diameter. A diamond should not weigh more than its
face-up size would indicate.
Both of these diamonds
have the same average
girdle diameters, which
gives them the same face-
up appearance of size.
But the diamond on the
right has a much thicker
girdle, so it weighs more.

Both by Al Gilbertson and Maha Tannous/GIA

Durability describes the potential amount of damage that can result from
unusually thin girdles or points, which make a diamond highly vulnerable during
normal jewelry wear.

The diamond on the left has

girdle areas that are very
thin and extremely thin,
making them vulnerable to
damage. The diamond on
the right has numerous
chips along the girdle.
Gary Roskin

Polish describes the overall quality and condition of the facet surfaces of a
finished diamond. It includes evaluation of any blemishes created by the
polishing process or during wear.

The diamond on the left

shows polish lines created
during the polishing
process. The diamond on
the right shows abraded
facet junctions caused by
wear. Both are considered
polish features.

Both by Mitchell Moore/GIA

Symmetry is the exactness of a finished diamond’s shape and the symmetrical

arrangement and even placement of its facets.

A round brilliant diamond

should have a symmetrical
outline (left). All eight of its
sections should match
each other (right).

89
DIAMOND GRADING LAB MANUAL

VISUAL EVALUATION OF FACE-UP

APPEARANCE
Using the GIA Cut Grading System, you evaluate a diamond’s face-up
appearance by analyzing its proportions. However, it is important to be able
to visually evaluate a diamond’s overall face-up appearance so you can:
• Recognize the appearances associated with each grade category.
• Understand and explain the differences in appearance among
diamonds of different grades, or the preferred appearances within a
single grade range.
Robert Weldon/GIA • Quickly evaluate a diamond without knowing its proportions, such
Visual evaluation of a diamond’s face-up as in a buying situation.
appearance includes individual assess-
ments of its brightness, pattern, and fire. In this section, you will learn how to visually assess a diamond’s bright-
ness, pattern, and fire. There’s no need for a separate evaluation of sparkle
(a component of scintillation along with pattern) because the observation
of brightness and fire takes into account the flashes of white and colored
light that you see as you move the diamond through a subtle range of
motion.
With practice, you can make a very accurate visual assessment of face-up
appearance. However, there are some limitations relating to the diamond’s
size and clarity:
• Size: It is difficult to evaluate differences in fire in diamonds
smaller than one-half carat (0.50 ct.). For those diamonds, you
should place more emphasis on brightness and pattern.
• Clarity: For low-clarity diamonds, formal assessment of their
proportions is more reliable than visual assessment. If the clarity is
I2 or I3, visual assessment does not apply.

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 DIAMOND GRADING LAB MANUAL

Viewing Environment
The same diamond can look quite different when it’s viewed in different
positions under different types of lighting. Also, diamonds reflect everything
around them, even a grader’s clothing. Therefore, a standardized viewing
environment is needed to make consistent and repeatable evaluations of a
diamond’s face-up appearance.
The GIA DiamondDock™ is designed to provide a standard viewing envi-
ronment. Its features provide the following:

A daylight-equivalent diffused fluorescent

light source for the evaluation of bright-
ness and pattern, and LED spotlighting
for the evaluation of fire

A neutral gray background

A neutral gray grading tray

Subdued, low-level ambient lighting

in the surrounding area

Eric Welch/GIA

You can create a similar controlled lighting environment using the diffused
overhead light source on a standard gemological microscope (for viewing
brightness and pattern) and an LED penlight (for viewing fire). The LED
penlight should have a suitable number of diodes. Five is sufficient—too
many can overemphasize fire and make it difficult to evaluate.

Overhead light source LED penlight

NOTE:
The color of the grading tray is
important. A white background
can make a diamond look
brighter by masking areas of light
leakage, while a black back-
ground can make the diamond
appear darker. The gray color has
no effect—positive or negative—
on a diamond’s appearance.

Both by Denise Conrad/GIA

91
DIAMOND GRADING LAB MANUAL

Evaluating Brightness
The first step in judging the diamond’s face-up appearance is to visually
evaluate its brightness.

To visually evaluate brightness:

1. Turn on the diffused fluorescent light source.
If using the DiamondDock™, be sure that only the fluorescent light
source is on and LED lights are off.
2. With a gemcloth, thoroughly clean the diamond being graded.
3. Use tweezers to place the diamond face-up in the gray grading tray.
4. Hold the tray 10 to 12 inches (25 to 30 cm) under the light source
and position yourself so the diamond is 12 to 18 inches (30 to 45 cm)
from your eyes.
• If you are using a DiamondDock™, hold the grading tray close
to the bottom of the environment.
• Be sure to center the tray under the light source.

1 4

Denise Conrad/GIA

Denise Conrad/GIA

Eric Welch/GIA Denise Conrad/GIA

92
 DIAMOND GRADING LAB MANUAL

5. Slowly tilt the tray back and forth through a subtle range of motion
to observe the diamond’s brightness. Assign a brightness grade of
excellent, very good, good, fair, or poor. You can use the rating
guidelines and examples below to help you assign the grade.

Excellent (EX): Stone appears very lively.

• Bright areas are evenly distributed across the
stone’s crown with no distracting dark areas.
• The area directly below the table facet, especially
around the culet, remains bright.

Very Good (VG): Stone appears lively.

• Bright areas are evenly distributed across the
stone’s crown, and there are few distracting areas.
• The area directly below the table facet remains
bright.

Good (G): Stone has some life.

• Some dark areas detract from the stone’s appear-
ance.
• The upper half facets, the area around the culet, or
both, might be dark.

Fair (F): Stone has little life.

• Some crown areas are bright, but large areas
might be gray.
• There might be concentrated areas of darkness or
dullness within the table area, around the girdle,
or both.

Poor (P): Stone appears dull and lifeless.

• Only small areas of the crown are bright.
• Table area might be very dark, and the dark area
might extend beyond the table into the
surrounding crown facets.
All by Eric Welch/GIA
• Upper half facets might be very dark and
distracting.

93
DIAMOND GRADING LAB MANUAL

Evaluating Pattern
After evaluating the diamond’s brightness, evaluate its pattern.

To visually evaluate pattern:

1. Use the same diffused fluorescent light source and viewing
distances as the ones used to evaluate brightness.
2. Slowly tilt the tray back and forth through a subtle range of motion.
3. As you observe the pattern, ask yourself these questions:
• Is the pattern pleasing? Is there attractive contrast between the
bright and dark areas?
• Is the pattern well balanced and symmetrical?
• Are there any dark areas that detract from the diamond’s
appearance?
4. Look for the following pattern defects, which detract from the
stone’s appearance and lower the grade.

All by Al Gilbertson and Barak Green/GIA

Fisheye—Pale gray reflection Dark center—A dark area in Dark upper half facets—The
of the girdle just inside the the center of the table. Stones upper half facets, or portions
diamond’s table facet. with this pattern are sometimes of them, appear dark or black.
referred to as “nailheads.”

Dark radiating mains—A Culet-in-bezel—Reflections Dark ring—A dark circular

dark spoke-like pattern of of the culet in the bezel area just inside the table
radiating pavilion mains. facets that produce a “busy” facet.
or confusing pattern.

NOTE:
Some patterns detract from a diamond’s appearance more than others. Fisheyes and
dark centers have very negative effects on a diamond’s appearance. Others, like dark
radiating mains and dark upper half facets, aren’t too distracting when slight.

94
 DIAMOND GRADING LAB MANUAL

5. Assign a pattern grade of excellent, very good, good, fair, or poor.

You can use the rating guidelines and examples below to help you
assign a grade.

Excellent (EX):

All by Al Gilbertson and Barak Green/GIA

• Very strong contrast between bright and dark.

• Stone is extremely attractive, with no distracting patterns.
• No pattern defects to minute pattern defects.
• Symmetrical radiating mains are permitted as long as they don’t
extend beyond the table facet or darken the area around the stone’s
culet.

Very Good (VG):

All by Al Gilbertson and Barak Green/GIA

• Strong contrast between bright and dark.

• Stone is very attractive, with minor pattern defects.
• Symmetrical radiating mains can extend under the crown facets but
the stone’s culet area must remain bright.
• Slight dark rings at the table edge are permitted.

95
DIAMOND GRADING LAB MANUAL

Good (G):

All by Al Gilbertson and Barak Green/GIA

• Some contrast between bright and dark.

• Stone can be attractive, but it has noticeable pattern defects.
• Radiating mains can extend under the crown facets and the stone’s
culet might be dark.
• Other patterns might include moderately dark upper half facets that
might give the stone’s girdle a chipped appearance.
• Table edges might display a dark ring.

Fair (F):

All by Al Gilbertson and Barak Green/GIA

• Little contrast between bright and dark.

• Typically unattractive, with obvious pattern defects.
• Many stones appear predominantly gray and might display
fisheyes.
• Area under the table typically appears dark or lifeless. In some
stones, dark upper half facets become more extreme and
distracting.
• Prominent dark radiating mains are common.

96
 DIAMOND GRADING LAB MANUAL

Poor (P):

All by Al Gilbertson and Barak Green/GIA

• Very little contrast between bright and dark.

• Overall impression is one of darkness with few bright areas.
• Prominent pattern defects distract the eye and make the diamond
extremely unattractive.
• A very dark area under the table facet (dark center) is common, and
it might be combined with extremely dark upper half facets and
very dark radiating mains.
• Stone might appear much smaller than its actual diameter because
upper half facets are so dark.
• Extreme fisheyes are also possible.

97
DIAMOND GRADING LAB MANUAL

1 Evaluating Fire
After evaluating the diamond’s brightness and pattern, evaluate its fire.

To visually evaluate fire:

1. Turn off the fluorescent light source and turn on the LED spotlighting.
2. As with brightness and pattern evaluation, hold the tray 10 to 12
inches (25 to 30 cm) under the light source and position yourself so
2
the diamond is 12 to 18 inches (30 to 45 cm) from your eyes.
• If using the DiamondDock™, hold the grading tray close to the
bottom of the environment. Be sure to center the tray under the
light source.
• If using a penlight, hold it 10 to 12 inches (25 to 30 cm) directly
over the diamond.

Both by Denise Conrad/GIA

NOTE:
Remember that it is difficult to evaluate differences in fire in diamonds
smaller than one-half carat (0.50 ct.). Therefore, for diamonds weighing
less than one-half carat, place more emphasis on your evaluation of bright-
ness and pattern.

98
 DIAMOND GRADING LAB MANUAL

3. Slowly tilt the tray back and forth through a subtle range of motion
to observe the diamond’s fire. Assign a fire grade of excellent, very
good, good, fair, or poor. Use the rating guidelines and examples
below to help you assign a grade.
• Excellent (EX): Bright flashes of fire appear across most of the
crown facets, so the stone looks very fiery. It is common to see a
greater variety of colors and flashes in the table.
• Very Good (VG): Flashes of fire appear across many of the
crown facets, so the stone looks fiery. It is common to see fewer
flashes of color in the table.
• Good (G): Some flashes of fire typically confined to the crown
facets. Stone can still be somewhat fiery.
• Fair (F): Small flashes of fire, which might be confined to small
areas of the diamond’s crown facets.
• Poor (P): Stone appears dull and lifeless.

Examples:

All by Eric Welch/GIA

Very Good Fair Poor

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DIAMOND GRADING LAB MANUAL

Plasma Etching
A nano-cutting process is sometimes used on polished diamonds to
enhance their appearance of fire. This process, called plasma etching,
involves etching a very fine nanoscale pattern onto the diamond’s surface
to disperse more light. A facet modified with plasma etching will appear
unpolished and display spectral colors. Plasma-etched diamonds are
marketed under the Fire Polish™ trademark.
Because the face-up appearance of the diamond has been altered, GIA
does not issue a cut grade. On GIA reports, it is described as having
“plasma-etching features.”

Robison McMurtry/GIA Robert Weldon/GIA

This diamond has plasma-etching features along its pavilion’s lower half
facet junctions (left). The etched features enhance the face-up appear-
ance of the diamond’s fire (right).

Etching is typically placed in a symmetrical pattern along the lower half

facet junctions or along the pavilion mains. These illustrations show
some possible etch patterns.

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 DIAMOND GRADING LAB MANUAL

EVALUATING PROPORTIONS AND DESIGN

You can assess a diamond’s face-up appearance and design by evaluating
its proportions, using a combination of measured parameters and visual
assessments.
This graphic illustrates the proportions that affect a diamond’s cut grade:

Star length
Table size

Crown angle
Crown height
Girdle
thickness

Total depth Pavilion angle

Pavilion depth

Lower half length

Culet size

A polished diamond is a tiny set of mirrors that interact with light to create
its face-up appearance of brightness, fire, and scintillation. Contributing to
that interaction are the diamond’s proportions—the angles and relative
measurements of its facets.
Using a combination of visual observation and computer models of the way
light behaves within diamonds, GIA researchers mapped the appearances
created by different sets of proportions and divided them into five cut-grade
ranges. This makes the GIA Cut Grading System predictive, meaning that
manufacturers can plan diamond cuts to achieve top grades. It also makes
it possible for you to easily and consistently evaluate the cut of a diamond.

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GIA Facetware® Cut Estimator

You can use the GIA Facetware® Cut Estimator software and database to
estimate a diamond’s cut grade. The database contains cut-grade results for
over 38.5 million proportion combinations and is available for use with most
leading optical measuring devices. It is also available free of charge for users
of web and mobile devices.
It is also possible, without using Facetware®, to use visual estimations, calcu-
lations, and look-up tables to estimate a cut grade with some degree of
accuracy. In this section, you will learn how to measure or estimate each
proportion and how they contribute to the overall cut grade—individually
and collectively.

Accuracy, Precision, and Tolerance

All measurements are assumed to have some degree of uncertainty associated
with them. This is often described as the measurement’s margin of error.
Measurement uncertainties can affect accuracy, and their use is essential
when determining precision.
• Accuracy describes how closely a given measurement matches the
actual value.
• Precision describes the exactness of the measurement, but not its
accuracy compared to the actual value.

In the GIA Cut Grading System, each proportion is rounded to a specific

level of precision based on:
• The accuracy and precision of the measuring devices and methods.
• The abilities of most diamond manufacturers to cut to each level of
precision.
• The differences in cut quality that can be seen by most observers.
People cannot see a visual difference between stones, beyond the
level of precision selected for the system.

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Tolerance is the range of variation that is allowed with repeated measurements.

For example, if a measuring device has a tolerance of +/- 0.01 mm, then a
result of 3.50 mm indicates an actual value between 3.49 and 3.51 mm. These
are some examples of tolerance:

-0.01 Actual Value +0.01

3.47 3.48 3.49
3.48 3.49 3.50
Measured
3.49 3.50 3.51
Result
3.50 3.51 3.52
3.51 3.52 3.53

A result might be out-of-tolerance if the measuring device being used is not

properly calibrated or maintained, or in the case of operator error. Visual
estimations will never reach the level of accuracy obtained with an optical
measuring device, but with practice you can come close.

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Weight Ratio and Overweight Percentage

Weight ratio is an analysis of the weight of the diamond relative to its average
girdle diameter. A diamond that is overweight or underweight can get a lower
cut grade. A diamond that weighs more than its diameter suggests is described
as “thick” or “heavy” in the trade. Added weight can be the result of a thick
girdle, high crown, deep pavilion, or any combination of these features.
WEIGHT INCREASES

GIA Facetware® calculates weight ratio using the diamond’s proportions

in order to determine its effect on the cut grade. When estimating a cut grade
without Facetware®, you will need to account for an overweight diamond
by calculating an overweight percentage. You will account for underweight
diamonds when you evaluate total depth percentage.

To calculate overweight percentage:

1. Round the average girdle diameter (AGD) to the nearest tenth of a
millimeter (0.1 mm).
2. In the table below, find the suggested weight for a diamond with
that same average girdle diameter.

These diamonds all have the

same average girdle diameter,
but the cutter added weight
by increasing their total depth
percentages.

S UGGESTED WEIGHT FOR DIAMETER

These are the suggested weights for a round brilliant diamond of a specific diameter with standard proportions,
including 60 percent total depth.
AGD (mm) Wt (ct.) AGD (mm) Wt (ct.) AGD (mm) Wt (ct.) AGD (mm) Wt (ct.)
2.9 0.09 4.6 0.35 6.3 0.90 8.0 1.91
3.0 0.10 4.7 0.37 6.4 0.94 8.1 1.98
3.1 0.11 4.8 0.40 6.5 1.00 8.2 2.05
3.2 0.12 4.9 0.42 6.6 1.03 8.3 2.13
3.3 0.13 5.0 0.45 6.7 1.08 8.4 2.21
3.4 0.14 5.1 0.48 6.8 1.13 8.5 2.29
3.5 0.15 5.2 0.50 6.9 1.18 8.6 2.37
3.6 0.17 5.3 0.53 7.0 1.23 8.7 2.45
3.7 0.18 5.4 0.57 7.1 1.33 8.8 2.54
3.8 0.20 5.5 0.60 7.2 1.39 8.9 2.62
3.9 0.21 5.6 0.63 7.3 1.45 9.0 2.71
4.0 0.23 5.7 0.66 7.4 1.51 9.1 2.80
4.1 0.25 5.8 0.70 7.5 1.57 9.2 2.90
4.2 0.27 5.9 0.74 7.6 1.63 9.3 2.99
4.3 0.29 6.0 0.78 7.7 1.70 9.4 3.09
4.4 0.31 6.1 0.81 7.8 1.77
4.5 0.33 6.2 0.86 7.9 1.83

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3. Compare the actual weight of the diamond to the suggested weight.

• If the diamond weighs the same as or less than the suggested
weight, it is not overweight. This means an overweight percent-
age is not applicable.
• If the diamond weighs more than the suggested weight, calculate
the overweight percentage. First, calculate the difference be-
tween the actual weight and the suggested weight. Then divide
this result by the suggested weight and multiply by 100. Round it
to the nearest whole percent (1%).

actual weight (ct.) — suggested weight (ct.)

Overweight % = x 100
suggested weight (ct.)

Round to nearest 1%

Example:
A round brilliant diamond has an average girdle diameter of 4.025 mm
and weighs 0.27 ct.
Rounded average girdle diameter = 4.025 = 4.0 mm
Suggested weight = 0.23 ct.
Overweight % = (0.27 – 0.23) ÷ 0.23 = 0.174
= 0.174 x 100 = 17.4
= 17%

Effect on Cut Grade

Overweight percentage limits the highest possible cut grade a diamond can
receive; the larger the percentage, the lower the possible cut grade.

GIA CUT G RADE AND OVERWEIGHT PERCENTAGE

This table lists the highest possible cut grade a diamond can receive based on its
overweight percentage. For example, a diamond with an overweight percentage of
9 percent would never qualify for excellent regardless of its other cut parameters.

Overweight % Highest Possible Cut Grade*

<9% EX
9% to16% VG
17% to 25% G
>25% F
*The overall cut grade might be lower due to another grading parameter or combination of proportions.
< means less than > means greater than

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Average girdle diameter Total Depth Percentage

The total depth percentage of a round brilliant diamond is the table-to-culet
depth, expressed as a percentage of the average girdle diameter and rounded
to the nearest tenth of a percent (0.1%).

Depth
To calculate total depth percentage:
1. Divide the depth in millimeters by the average girdle diameter and
multiply by 100.
2. Round the result to the nearest tenth of a percent (0.1%).

depth (mm)
Total Depth % = x 100
average girdle diameter (mm)

Round to nearest 0.1%

Example:
A round brilliant diamond has a minimum girdle diameter of 4.56 mm, a
maximum diameter of 4.59 mm and a depth of 2.56 mm.
Average girdle diameter = 4.56 + 4.59 ÷ 2 = 4.575
Total depth % = (2.56 ÷ 4.575) x 100 = 55.95628
= 56.0%

NOTE:
Total depth percentage calculated using diameter and depth measure-
ments rounded to the hundredths place might differ from the total depth
on a GIA Report by 0.1% or 0.2%. The optical measuring devices used
by the laboratory deliver diameter and depth measurements to the
thousandths place, and those figures—without being rounded—are used to
calculate total depth percentage.

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Effect on Cut Grade

Total depth percentage is used to calculate a diamond’s weight ratio—
whether it is underweight or overweight in relation to its diameter. It is also
an important indicator of the diamond’s overall proportions.

55% 60% 65%

A diamond with a total depth below 55.0 percent is generally underweight, with a shallow
crown, shallow pavilion, thinner girdle, or any combination of these (left). A diamond with
a total depth of 65.0 percent or more is generally overweight, with a high crown, deep
pavilion, thicker girdle, or any combination of these (right). A well-proportioned diamond
with a 60.0 percent total depth percentage is shown for comparison (center).

60% 60% 60%

A well-proportioned diamond (left) typically has a total depth near 60.0 percent. While
this generally indicates good proportions, it doesn’t guarantee them. For example, the
diamond might have a shallow or high crown, shallow or deep pavilion, or a thick
girdle (center and right).

GIA CUT G RADE AND TOTAL DEPTH PERCENTAGE

This table lists the highest possible cut grade a diamond can receive based
on its total depth percentage. For example, a diamond with a total depth
of 57.4 percent would never qualify for excellent regardless of its other cut
parameters.

Total Depth % Highest Possible Cut Grade*

<51.0% P

51.0% to 52.9% F

53.0% to 55.9% G

56.0% to 57.4% VG

57.5% to 63.0% EX

63.1% to 64.5% VG

64.6% to 66.5% G

66.6% to 70.9% F

>70.9% P

*The overall cut grade might be lower due to another grading parameter or combination of proportions.
< means less than > means greater than

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Average girdle diameter Table Percentage

Average table size The table percentage of a round brilliant diamond is the average of four table
measurements expressed as a percentage of the average girdle diameter and
rounded to the nearest whole percent (1%).
You can measure the table directly using a table gauge or visually estimate
table percentage using the “flash,” “ratio,” or “bowing” methods. If you are
not using an optical measuring device, direct measurement with a table
gauge is the most accurate method.

Direct Measurement
To determine table percentage using a table gauge:
1. Hold the diamond face-up and girdle-to-girdle, under magnifica-
tion, using darkfield illumination or a combination of darkfield and
overhead lighting.

Both by Denise Conrad/GIA

You can use tweezers to hold the diamond (left), but it might be easier to use the iris
diaphragm. To do this, close the diaphragm and place the diamond’s culet in the
small opening (right).

2. Press the table gauge flat against the table and measure the four
corner-to-corner table distances.

Denise Conrad/GIA

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• To take a measurement, line up the zero-point of the gauge with

a table corner and take the reading at the opposing table corner.
If the measuring set-up is correct, you will see four star facets
below the table gauge.
• Each unit on the table gauge is equal to 0.10 mm. You’ll need to
estimate each measurement to the nearest 0.05 mm. If the meas-
urement falls on or close to a line, your measurement will end in
0. If the measurement falls in the middle, your measurement will
end in 5 (for example, 4.95 mm).

5
0 1 2 3 4 5 6 7

1 4
2 3

4.90 4.95 5.00

UNITS = .1mm
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

3. Calculate the table percentage.

• Add the four table size measurements and divide by 4 to average
them; do not round.
• Divide the average table size by the average girdle diameter and
multiply by 100.
• Round the result to the nearest whole percent (1%).

average table size (mm)

Table % = x 100
average girdle diameter (mm)

Round to nearest 1%

Example:
A round brilliant diamond has a minimum diameter of 4.52 mm and a
maximum diameter of 4.55 mm. Table size measurements are 2.55, 2.50,
2.55, and 2.50 mm.
Average girdle diameter = 4.52 + 4.55 ÷ 2 = 4.535
Average table size = 2.55 + 2.50 + 2.55 + 2.50 = 10.1 ÷ 4 = 2.525 mm
Table % = 2.525 ÷ 4.535 = 0.5567805
= 0.5567805 x 100 = 55.67805
= 56%

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Ratio Method
To visually estimate table percentage using the ratio method:
1. Hold the diamond face-up and girdle-to-girdle, under magnifica-
tion, using darkfield illumination.
2. Visually center the culet. If the culet is off-center, you will need to
tilt the stone so it appears centered.

1 2

Denise Conrad/GIA Derek Sharpe/GIA

3. Compare the distance from the edge of the girdle to the side of the
table (A) to the distance from the side of the table to the center of
the table, where you see the culet (B). Then, determine the ratio
between them (A:B). Check the ratio on opposing sides of the stone
before you settle on your estimate.

Distance A = 1
Distance B = number of times longer it is
than A

For example, if distance B is twice as long

as distance A, the ratio is 1:2.

A B

4. Use this ratio to estimate the table percentage. Common ratios and
their corresponding table percentages are shown in the illustrations
on the next page. If the ratio falls outside of, or between, these
figures, you will need to estimate an intermediate percentage.
5. Adjust your estimate as follows if the table is not a regular octagon:
• Add 1% if the variation is slight.
• Add 2% if the variation is noticeable.

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Common Ratios and their Corresponding Table

Percentage Estimates
SMALLER TABLES

1 1 54%

1 11/4 60%

1 11/2 65%

1 13/4 69%
LARGER TABLES

1 2 72%

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Bowing Method
To estimate table percentage using the bowing method:
1. Examine the diamond face-up and girdle-to-girdle under magnifica-
tion, using darkfield illumination.
2. Look for the two squares formed by table and star facet junctions.

1 2

Denise Conrad/GIA

3. Estimate an overall table percentage according to how much the

sides of the two squares bow in or out.
• Use the illustrations and descriptions on the next page to help
you estimate the percentage.
• If the appearance falls outside of or between these figures, you
will need to estimate an intermediate percentage.
4. If necessary, adjust your estimate to account for the length of the
star facets. Star facets normally extend half the distance between
the girdle and the table edge. Longer star facets make the line bow
in more, while shorter facets make the line bow out more.
Adjust your estimate based on the length of the star facets as follows:
• Add between 1% and 6% if the star facets extend more than
halfway to the girdle.
• Subtract between 1% and 6% if star facets extend less than
halfway to the girdle.
For example, these diamonds all have 60 percent table sizes:

1/3; subtract 6% 1/2; no adjustment 2/3; add 6%

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5. Adjust your estimate as follows if the table is not a regular octagon:

• Add 1% if the variation is slight.
• Add 2% if the variation is noticeable.

Bowing Appearances and their Corresponding Table

Percentage Estimates
SMALLER TABLES

53%
Bows in noticeably

58%
Bows in slightly

60%
Straight

63%
Bows out slightly
LARGER TABLES

67%
Bows out noticeably

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Flash Method
The flash method is a quick and easy way to estimate a diamond’s table
percentage. It’s especially useful if you want to rapidly compare and sort a
large number of stones that don’t have to match exactly.

To estimate table percentage using the flash method:

1. Examine the diamond face-up and girdle-to-girdle with your
unaided eye, under an overhead light source.
2. Slowly rock and tilt the diamond to observe the flash of white light
that reflects off the table.
3. Estimate the table percentage based on your perception of the size
of the flash compared to the entire face-up view of the stone—
small, medium, or large. Then, refine your estimate to a single
percentage. You can use the examples provided here to help you
estimate the percentage.

All by John Koivula/GIA

Small flash: 53% to 59% Medium flash: 60% to 64% Large flash: 65% or larger

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Effect on Cut Grade

Table size can have a significant impact on the diamond’s face-up appearance,
especially when it’s paired with certain combinations of crown and pavilion
angles. A table that is very small or very large tends to have a negative effect
on a diamond’s face-up appearance. Table size directly affects the appearance
of brightness and fire.
• If all other factors are equal, stones with table percentages in the
middle to upper 50-percent ranges produce more fire.
• Fire tends to decrease as the table percentage increases because it
leaves a smaller area of crown facets to produce fire.
• Larger tables show more brightness and less fire.

GIA CUT G RADE AND TABLE PERCENTAGE

This table lists the highest possible cut grade a diamond can receive based on its table
percentage. For example, a diamond with a table size of 51 percent would never qualify
for excellent regardless of its other cut parameters.

Table % Highest Possible Cut Grade*

< 44% P

44% to 46% F

47% to 49% G

50% to 51% VG

52% to 62% EX

63% to 66% VG

67% to 69% G

70% to 72% F

> 72% P
*The overall cut grade might be lower due to another grading parameter or combination of proportions.
< means less than > means greater than

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Star Length Percentage

Girdle-to-girdle distance Star length percentage is the length of the star facet expressed as a percentage
Star facet length of the girdle-to-table distance. The average of the eight star length
percentages is rounded to the nearest five percent (5%).

To visually estimate star length percentage:

1. Examine the diamond face-up and girdle-to-girdle under magnifi-
cation, using darkfield illumination.
2. Consider the distance between the edge of the table and the girdle
as 100 percent.
3. Estimate the distance each star facet reaches toward the girdle.
• Start with one star facet and move in a consistent direction until
you’ve examined all eight star facets.
: 0% 100%
• Use the illustrations below to help you estimate the percentage.

4. Average your eight estimates and round that figure to the nearest
five percent (5%).

35% 40% 45% 50%

55% 60% 65% 70%

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Effect on Cut Grade

Alone, star length percentage has a limited effect on the overall cut grade.
However, when they are very short or very long, star facets can have a
negative effect on a diamond’s face-up appearance, especially brightness
and fire.

GIA CUT G RADE AND STAR LENGTH PERCENTAGE

This table lists the highest possible cut grade a diamond can receive based on its star
length percentage. For example, a diamond with a star length of 40 percent would
never qualify for excellent regardless of its other cut parameters.

Star Length % Highest Possible Cut Grade*

< 40% G

40% VG

45% to 65% EX

70% VG

> 70% G

*The overall cut grade might be lower due to another grading parameter or combination of proportions.
< means less than > means greater than

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Crown Angle
crown angle Crown angle is the measured angle between the bezel facet plane and the
table plane. The average of eight crown angle measurements is rounded to
the nearest 0.5 degrees.
You can visually estimate crown angle using a crown angle reference card
or by using the “profile” or “face-up” methods explained on the following
pages. If you are not using an optical measuring device, examining the
diamond using a crown angle reference card is the most accurate method.

Crown Angle Reference Card

To estimate crown angle using a crown angle reference card:
1. Place the crown angle reference card over the microscope’s well
light. Note that the card has two scales, one for left-handed use and
one for right-handed use. Hold the diamond in profile view, table-
to-culet, over the card. Examine the diamond under magnification
using a combination of darkfield and overhead lighting.

24 26 28 30 32 34 36 38 40 42 44

2. Turn the diamond so the bezel surface is flat in profile.

a r

Bezel facet flat in profile Star and upper half facet in profile

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3. Line up the table plane with the horizontal baseline on the card. You
will not get an accurate estimate if the table is not parallel with this
line or if the diamond is tilted in any direction.

36 38 40

4. Holding the diamond still, move the card to the left and right to find
the best fit between the bezel plane and an angle line on the card.
The closest angle will be as parallel as possible to the bezel, with
equal spacing between the diamond and the top and bottom of the
line.

36 38 40 40 42 44

In this illustration, the crown angle is parallel to the 36-degree The crown angle is not parallel to the 40-degree line. Notice
line. Notice the equal spacing bettween the line and the top the unequal spacing between the line and the top and bottom
and bottom of the bezel. of the bezel.

5. You’ll need to estimate values between the lines to the nearest

0.5%.
6. Rotate the diamond to determine if the crown angles are symmetrical.
• If they are, one estimate is sufficient.
• If they vary, you will need to estimate all eight crown angles and
average them.

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Profile Method
To estimate crown angle using the profile method:
1. Hold the diamond table-to-culet in profile view, under magnifica-
tion, using darkfield illumination.
Turn the diamond so the bezel surface is flat in profile.

a r

Bezel facet flat in profile Star and upper half facet in profile

2. Examine the angle of the bezel facet in relation to the table plane.
You can use the tweezers as a reference.
• Remember that a right angle is 90°, half a right angle is 45°, and
one-third is 30°.
• You can compare other angles to these convenient references.

45° 30° 25° 30°

34°

45°
60°
90 90° 90°

40° 38° 36° 34.5° 32° 30° 26°

Steep Moderately Slightly Slightly Moderately Shallow

steep steep shallow shallow

3. Rotate the diamond and examine all eight bezel facets to mentally
arrive at an average angle.

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Face-up Method
If it is not possible to examine the diamond with the profile method, you can
estimate crown angle face-up by using the appearance of the pavilion main
facet as seen through the crown. This method is especially helpful for
mounted diamonds. This method is not as accurate with tables less than 55
percent or greater than 65 percent.

To estimate crown angle using the face-up method:

1. Examine the diamond girdle-to-girdle and face-up under 10X
magnification, using darkfield illumination.
2. Look through the table and locate one of the pavilion main facets.
3. Compare the width of the pavilion main where it meets the table
corner (A) to its width at the top point of the bezel facet (B).

A
B

4. Use the descriptions listed below to help you estimate the crown
angle. Note that the greater the difference between the two widths,
the steeper the crown angle.

FACE-UP M ETHOD

60% table Crown Angle Width of Main

25°
25° Same width in table and bezel

30° Slightly wider in bezel

30°
34.5° Nearly twice as wide in the bezel

39° More than twice as wide in the bezel

34.5°
39° steep Entire image of the pavilion main, and
≥40°
sometimes even the culet reflection

≥ means greater than or equal to

5. Compare all eight pavilion mains and decide on an overall estimate.

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Effect on Cut Grade

Crown angle can significantly affect a diamond’s face-up appearance.
Generally, crown angles from 32 to 36 degrees produce attractive, bright, and
fiery diamonds if combined with the right table percentage and pavilion angle.

GIA CUT G RADE AND CROWN ANGLE

This table lists the highest possible cut grade a diamond can receive based on its
crown angle. For example, a diamond with a crown angle of 37.0 degrees would never
qualify for excellent regardless of its other cut parameters.

Crown Angle Highest Possible Cut Grade*

<20.0° P

20.0° to 21.5° F

22.0° to 26.0° G

26.5° to 31.0° VG

31.5° to 36.5° EX

37.0° to 38.5° VG

39.0° to 40.0° G

40.5° to 41.5° F

>41.5° P
*The overall cut grade might be lower due to another grading parameter or combination of proportions.
< means less than > means greater than

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Crown Height Percentage Average girdle diameter

Crown height percentage is the diamond’s crown height, measured from the
Crown
table to the intersection of the bezel facet and the girdle, expressed as a height
percentage of its average girdle diameter. Crown height percentage is
rounded to the nearest half of a percent (0.5%).
The height of a diamond’s crown is directly related to its table percentage
and crown angle. You can use the table on pages 124 and 125 to estimate
crown height percentage.

Effect on Cut Grade

Along with pavilion depth and girdle thickness, crown height can affect the
diamond’s weight ratio. In general, a high crown (17.0 percent or larger)
adds unnecessary weight.

GIA CUT G RADE AND CROWN H EIGHT PERCENTAGE

This table lists the highest possible cut grade a diamond can receive based on its
average crown height percentage. For example, a diamond with a crown height of
18.5 percent would never qualify for excellent regardless of its other cut parameters.

Crown Height % Highest Possible Cut Grade*

<7.0% P

7.0% to 8.5% F

9.0% to 10.0% G

10.5% to 12.0% VG

12.5% to 17.0% EX

17.5% to 18.0% VG

18.5% to 19.5% G

20.0% to 21.0% F

>21.0% P

*The overall cut grade might be lower due to another grading parameter or combination of proportions.
< means less than > means greater than

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E STIMATED CROWN H EIGHT PERCENTAGE

To estimate the crown height percentage, you have to know the diamond’s table percentage and its crown
angle. Once you’ve determined these figures, find the appropriate table percentage in the chart and follow that
row across to the correct average crown angle column. For example, if the table is 60% and the crown angle

Average Crown Angle

20.5° 21° 21.5° 22° 22.5° 23° 23.5° 24° 24.5° 25° 25.5° 26° 26.5° 27° 27.5° 28° 28.5° 29° 29.5° 30° 30.5°

48 9.5 10.0 10.0 10.5 11.0 11.0 11.5 11.5 12.0 12.0 12.5 12.5 13.0 13.0 13.5 14.0 14.0 14.5 14.5 15.0 15.5

49 9.5 10.0 10.0 10.5 10.5 11.0 11.0 11.5 11.5 12.0 12.0 12.5 12.5 13.0 13.5 13.5 14.0 14.0 14.5 14.5 15.0

50 9.5 9.5 10.0 10.0 10.5 10.5 11.0 11.0 11.5 11.5 12.0 12.0 12.5 12.5 13.0 13.5 13.5 14.0 14.0 14.5 14.5

51 9.0 9.5 9.5 10.0 10.0 10.5 10.5 11.0 11.0 11.5 11.5 12.0 12.0 12.5 13.0 13.0 13.5 13.5 14.0 14.0 14.5

52 9.0 9.0 9.5 9.5 10.0 10.0 10.5 10.5 11.0 11.0 11.5 11.5 12.0 12.0 12.5 13.0 13.0 13.5 13.5 14.0 14.0

53 9.0 9.0 9.5 9.5 9.5 10.0 10.0 10.5 10.5 11.0 11.0 11.5 11.5 12.0 12.0 12.5 13.0 13.0 13.5 13.5 14.0

54 8.5 9.0 9.0 9.5 9.5 10.0 10.0 10.0 10.5 10.5 11.0 11.0 11.5 11.5 12.0 12.0 12.5 12.5 13.0 13.5 13.5

55 8.5 8.5 9.0 9.0 9.5 9.5 10.0 10.0 10.5 10.5 10.5 11.0 11.0 11.5 11.5 12.0 12.0 12.5 12.5 13.0 13.5

56 8.0 8.5 8.5 9.0 9.0 9.5 9.5 10.0 10.0 10.5 10.5 10.5 11.0 11.0 11.5 11.5 12.0 12.0 12.5 12.5 13.0

57 8.0 8.5 8.5 8.5 9.0 9.0 9.5 9.5 10.0 10.0 10.5 10.5 10.5 11.0 11.0 11.5 11.5 12.0 12.0 12.5 12.5

58 8.0 8.0 8.5 8.5 8.5 9.0 9.0 9.5 9.5 10.0 10.0 10.0 10.5 10.5 11.0 11.0 11.5 11.5 12.0 12.0 12.5
Table Percentage

59 7.5 8.0 8.0 8.5 8.5 8.5 9.0 9.0 9.5 9.5 10.0 10.0 10.0 10.5 10.5 11.0 11.0 11.5 11.5 12.0 12.0

60 7.5 7.5 8.0 8.0 8.5 8.5 8.5 9.0 9.0 9.5 9.5 10.0 10.0 10.0 10.5 10.5 11.0 11.0 11.5 11.5 12.0

61 7.5 7.5 7.5 8.0 8.0 8.5 8.5 8.5 9.0 9.0 9.5 9.5 9.5 10.0 10.0 10.5 10.5 11.0 11.0 11.5 11.5

62 7.0 7.5 7.5 7.5 8.0 8.0 8.5 8.5 8.5 9.0 9.0 9.5 9.5 9.5 10.0 10.0 10.5 10.5 10.5 11.0 11.0

63 7.0 7.0 7.5 7.5 7.5 8.0 8.0 8.0 8.5 8.5 9.0 9.0 9.0 9.5 9.5 10.0 10.0 10.5 10.5 10.5 11.0

64 6.5 7.0 7.0 7.5 7.5 7.5 8.0 8.0 8.0 8.5 8.5 9.0 9.0 9.0 9.5 9.5 10.0 10.0 10.0 10.5 10.5

65 6.5 6.5 7.0 7.0 7.0 7.5 7.5 8.0 8.0 8.0 8.5 8.5 8.5 9.0 9.0 9.5 9.5 9.5 10.0 10.0 10.5

66 6.5 6.5 6.5 7.0 7.0 7.0 7.5 7.5 7.5 8.0 8.0 8.5 8.5 8.5 9.0 9.0 9.0 9.5 9.5 10.0 10.0

67 6.0 6.5 6.5 6.5 7.0 7.0 7.0 7.5 7.5 7.5 8.0 8.0 8.0 8.5 8.5 9.0 9.0 9.0 9.5 9.5 9.5

68 6.0 6.0 6.5 6.5 6.5 7.0 7.0 7.0 7.5 7.5 7.5 8.0 8.0 8.0 8.5 8.5 8.5 9.0 9.0 9.0 9.5

69 6.0 6.0 6.0 6.5 6.5 6.5 6.5 7.0 7.0 7.0 7.5 7.5 7.5 8.0 8.0 8.0 8.5 8.5 9.0 9.0 9.0

70 5.5 6.0 6.0 6.0 6.0 6.5 6.5 6.5 7.0 7.0 7.0 7.5 7.5 7.5 8.0 8.0 8.0 8.5 8.5 8.5 9.0

71 5.5 5.5 5.5 6.0 6.0 6.0 6.5 6.5 6.5 7.0 7.0 7.0 7.0 7.5 7.5 7.5 8.0 8.0 8.0 8.5 8.5

72 5.0 5.5 5.5 5.5 6.0 6.0 6.0 6.0 6.5 6.5 6.5 7.0 7.0 7.0 7.5 7.5 7.5 8.0 8.0 8.0 8.0

73 5.0 5.0 5.5 5.5 5.5 5.5 6.0 6.0 6.0 6.5 6.5 6.5 6.5 7.0 7.0 7.0 7.5 7.5 7.5 8.0 8.0

74 5.0 5.0 5.0 5.5 5.5 5.5 5.5 6.0 6.0 6.0 6.0 6.5 6.5 6.5 7.0 7.0 7.0 7.0 7.5 7.5 7.5

75 4.5 5.0 5.0 5.0 5.0 5.5 5.5 5.5 5.5 6.0 6.0 6.0 6.0 6.5 6.5 6.5 7.0 7.0 7.0 7.0 7.5

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is 30°, the estimated crown height would be 11.5%.

If the crown angle is greater than 40.5°, use the value in the 40.5° column. For example, if the table is 63% and
the crown angle is 42.0°, the crown height would be 16.0%.

Average Crown Angle

31° 31.5° 32° 32.5° 33° 33.5° 34° 34.5° 35° 35.5° 36° 36.5° 37° 37.5° 38° 38.5° 39° 39.5° 40° 40.5°

15.5 16.0 16.0 16.5 17.0 17.0 17.5 18.0 18.0 18.5 19.0 19.0 19.5 20.0 20.5 20.5 21.0 21.5 22.0 22.0 48

15.5 15.5 16.0 16.0 16.5 17.0 17.0 17.5 18.0 18.0 18.5 19.0 19.0 19.5 20.0 20.5 20.5 21.0 21.5 22.0 49

15.0 15.5 15.5 16.0 16.0 16.5 17.0 17.0 17.5 18.0 18.0 18.5 19.0 19.0 19.5 20.0 20.0 20.5 21.0 21.5 50

14.5 15.0 15.5 15.5 16.0 16.0 16.5 17.0 17.0 17.5 18.0 18.0 18.5 19.0 19.0 19.5 20.0 20.0 20.5 21.0 51

14.5 14.5 15.0 15.5 15.5 16.0 16.0 16.5 17.0 17.0 17.5 18.0 18.0 18.5 19.0 19.0 19.5 20.0 20.0 20.5 52

14.0 14.5 14.5 15.0 15.5 15.5 16.0 16.0 16.5 17.0 17.0 17.5 17.5 18.0 18.5 18.5 19.0 19.5 19.5 20.0 53

14.0 14.0 14.5 14.5 15.0 15.0 15.5 16.0 16.0 16.5 16.5 17.0 17.5 17.5 18.0 18.5 18.5 19.0 19.5 19.5 54

13.5 14.0 14.0 14.5 14.5 15.0 15.0 15.5 16.0 16.0 16.5 16.5 17.0 17.5 17.5 18.0 18.0 18.5 19.0 19.0 55

13.0 13.5 13.5 14.0 14.5 14.5 15.0 15.0 15.5 15.5 16.0 16.5 16.5 17.0 17.0 17.5 18.0 18.0 18.5 19.0 56

13.0 13.0 13.5 13.5 14.0 14.0 14.5 15.0 15.0 15.5 15.5 16.0 16.0 16.5 17.0 17.0 17.5 17.5 18.0 18.5 57

12.5 13.0 13.0 13.5 13.5 14.0 14.0 14.5 14.5 15.0 15.5 15.5 16.0 16.0 16.5 16.5 17.0 17.5 17.5 18.0 58

Table Percentage
12.5 12.5 13.0 13.0 13.5 13.5 14.0 14.0 14.5 14.5 15.0 15.0 15.5 15.5 16.0 16.5 16.5 17.0 17.0 17.5 59

12.0 12.5 12.5 12.5 13.0 13.0 13.5 13.5 14.0 14.5 14.5 15.0 15.0 15.5 15.5 16.0 16.0 16.5 17.0 17.0 60

11.5 12.0 12.0 12.5 12.5 13.0 13.0 13.5 13.5 14.0 14.0 14.5 14.5 15.0 15.0 15.5 16.0 16.0 16.5 16.5 61

11.5 11.5 12.0 12.0 12.5 12.5 13.0 13.0 13.5 13.5 14.0 14.0 14.5 14.5 15.0 15.0 15.5 15.5 16.0 16.0 62

11.0 11.5 11.5 12.0 12.0 12.0 12.5 12.5 13.0 13.0 13.5 13.5 14.0 14.0 14.5 14.5 15.0 15.5 15.5 16.0 63

11.0 11.0 11.0 11.5 11.5 12.0 12.0 12.5 12.5 13.0 13.0 13.5 13.5 14.0 14.0 14.5 14.5 15.0 15.0 15.5 64

10.5 10.5 11.0 11.0 11.5 11.5 12.0 12.0 12.5 12.5 12.5 13.0 13.0 13.5 13.5 14.0 14.0 14.5 14.5 15.0 65

10.0 10.5 10.5 11.0 11.0 11.5 11.5 11.5 12.0 12.0 12.5 12.5 13.0 13.0 13.5 13.5 14.0 14.0 14.5 14.5 66

10.0 10.0 10.5 10.5 10.5 11.0 11.0 11.5 11.5 12.0 12.0 12.0 12.5 12.5 13.0 13.0 13.5 13.5 14.0 14.0 67

9.5 10.0 10.0 10.0 10.5 10.5 11.0 11.0 11.0 11.5 11.5 12.0 12.0 12.5 12.5 12.5 13.0 13.0 13.5 13.5 68

9.5 9.5 9.5 10.0 10.0 10.5 10.5 10.5 11.0 11.0 11.5 11.5 11.5 12.0 12.0 12.5 12.5 13.0 13.0 13.0 69

9.0 9.0 9.5 9.5 9.5 10.0 10.0 10.5 10.5 10.5 11.0 11.0 11.5 11.5 11.5 12.0 12.0 12.5 12.5 13.0 70

8.5 9.0 9.0 9.0 9.5 9.5 10.0 10.0 10.0 10.5 10.5 10.5 11.0 11.0 11.5 11.5 11.5 12.0 12.0 12.5 71

8.5 8.5 8.5 9.0 9.0 9.5 9.5 9.5 10.0 10.0 10.0 10.5 10.5 10.5 11.0 11.0 11.5 11.5 11.5 12.0 72

8.0 8.5 8.5 8.5 9.0 9.0 9.0 9.5 9.5 9.5 10.0 10.0 10.0 10.5 10.5 10.5 11.0 11.0 11.5 11.5 73

8.0 8.0 8.0 8.5 8.5 8.5 9.0 9.0 9.0 9.5 9.5 9.5 10.0 10.0 10.0 10.5 10.5 10.5 11.0 11.0 74

7.5 7.5 8.0 8.0 8.0 8.5 8.5 8.5 9.0 9.0 9.0 9.0 9.5 9.5 10.0 10.0 10.0 10.5 10.5 10.5 75

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DIAMOND GRADING LAB MANUAL

Culet Size
Culet size is described as the width of the culet facet, when present, relative
to a round diamond’s average girdle diameter at 10X magnification. Culet
size can range from none to extremely large.
Diamonds with undamaged or non-abraded points rather than culets are
sometimes described as “pointed.”
Culet
To determine culet size:
1. Examine the diamond face-up and girdle-to-girdle, under 10X
magnification with darkfield illumination.
2. Looking through the table at the culet area, compare the size of the
culet relative to the size of the diamond.

Culet size 3. Assign a culet size of none, very small, small, medium, slightly
large, large, very large, or extremely large.
• Use the illustrations and descriptions below to help you estimate
culet size.
• Some additional considerations are listed in the next section.

None (NON): Very small (VSM): Small (SML): Medium (MED):

No culet facet Barely distinguishable at 10X Difficult to see at 10X Distinct at 10X

Slightly large (SLG): Large (LRG): Very large (VLG): Extremely large (ELG):
Obvious at 10X Very obvious at 10X Distracting at 10X Very distracting at 10X

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 DIAMOND GRADING LAB MANUAL

Special Case Guidelines for Culet Size

These are some special case guidelines you will need to consider when you
assess culet size.
• If there is no culet facet, assign a culet size of “none.” A pointed,
abraded culet looks like a tiny white speck. You might need higher
magnification to distinguish between none and very small.
• When there’s a chip, cavity, or indented natural that covers the
entire culet area, assign a culet size of none. If only a portion of the
culet facet remains, consider that in your culet size assessment. In
any case, include the characteristic in the diamond’s clarity grade.
• The culet facet should be parallel to the table facet. If the culet is at
more than a slight angle to the table facet, consider it an extra facet
rather than a culet and assign a culet size of none. You can hold the
diamond girdle-to-girdle and examine it in profile view to deter-
mine the culet’s angle.
• Sometimes a cutter leaves the culet as an unpolished natural
surface. If it’s nearly parallel to the table facet, consider it a culet
and assign the appropriate size description. The natural is also
included in the diamond’s clarity grade.

None Very small

None: chipped Slightly large: natural at culet area

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Effect on Cut Grade

A culet size of none, very small, or small has no effect on the cut grade.
Larger culets, however, can have a negative effect on the diamond’s face-up
appearance, specifically affecting its pattern. In general, the larger the culet,
the lower the cut grade.

GIA CUT G RADE AND CULET S IZE

This table lists the highest possible cut grade a diamond can receive based on its culet
size. For example, a diamond with a culet size of medium would never qualify for
excellent regardless of its other cut parameters.

Culet Size Highest Possible Cut Grade*

NON, VSM, SML EX

MED VG

SLG, LRG G

VLG F

ELG P

*The overall cut grade might be lower due to another grading parameter or combination of proportions.

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 DIAMOND GRADING LAB MANUAL

Average girdle diameter

Pavilion Depth Percentage and Pavilion Angle
Pavilion depth percentage is the diamond’s pavilion depth, measured from
the culet to the intersection of the pavilion main facet and the girdle,
expressed as a percentage of its average girdle diameter. Pavilion depth

Pavilion depth
percentage is rounded to the nearest half of a percent (0.5%). The depth of
a diamond’s pavilion is directly related to its pavilion angle and culet size.
Pavilion angle is the measured angle between the pavilion main facet plane
and the table plane. The average of eight pavilion angle measurements is
rounded to the nearest 0.2 degrees.
Pavilion angle
To visually estimate pavilion depth percentage and pavilion angle:
1. Examine the diamond face-up and girdle-to-girdle, under 10X
magnification with darkfield illumination.
2. Center the culet in the table and look for the reflection of the table
facet on the pavilion mains. It’s often outlined by connected “bow-
ties,” which are reflections of the star facets in the pavilion mains.
Disregard any reflections you see in the lower half facets.

Star facet reflections help you see the You can also use a pointer to locate the Star facets rarely form a perfect outline
reflection of the table. table reflection. Place its point at a table of the table’s reflection. Misaligned
corner. The pointer’s reflection on the facets might make some reflections
other side of the stone shows you the appear tilted, and some might not be
location of the table reflection. visible.

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DIAMOND GRADING LAB MANUAL

3. Estimate the pavilion depth percentage to the nearest 0.5 percent,

based on how far the table reflection extends from the culet to the
table corner.
• Use the illustrations and descriptions below to help you estimate
the percentage.
• If the appearance falls outside of, or between, these figures, you
will need to estimate an intermediate percentage.

< 41.0% 45.5%

Table reflection breaks up About 2/3 of distance

42.0% 47.0%
About 1/4 of distance About 3/4 of distance

43.0% 49.0%
About 1/3 of distance Reflection fills table and looks dark

44.5% >50.0%
About 1/2 of distance Table and star facets look dark

< means less than > means greater than

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4. Use your estimated pavilion depth percentage with the table on

page 132 to determine the pavilion angle.
5. Adjust your pavilion depth percentage estimate, if necessary, based
on culet size. If culet size is none, no adjustment is needed.
• As the culet gets larger, the pavilion depth gets shallower.
• The table reflection indicates the correct corresponding pavilion
angle regardless of culet size.

40.8° 40.8°
43.0% 40.0%

These two diamonds show the same table reflection, and have the same pavilion
angle of 40.8°. However, the diamond on the right has a large culet, which makes its
pavilion depth shallower.

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E STIMATED PAVILION DEPTH % AND PAVILION ANGLE

To estimate the pavilion depth and Visual

Pavilion Adjust pavilion depth % if the culet is:
pavilion angle: Pavilion
Angle VSM SML MED SLG LRG VLG ELG
Depth %
1. Visually estimate the pavilion depth 37.5 36.8 37.0 37.0 36.5 35.5 35.0 33.5 32.0
percentage using the illustrations on
37.5 37.0 37.5 37.0 36.5 36.0 35.0 33.5 32.0
page 130 of this manual.
38.0 37.2 38.0 37.5 37.0 36.0 35.5 34.0 32.5
38.0 37.4 38.0 37.5 37.0 36.5 35.5 34.0 32.5
2. Find the value in the first column that
38.5 37.6 38.5 38.0 37.5 36.5 36.0 34.5 32.5
matches your visual pavilion depth
percentage estimate and its 39.0 37.8 38.5 38.0 37.5 37.0 36.0 34.5 33.0
corresponding pavilion angle. 39.0 38.0 39.0 38.5 38.0 37.0 36.5 35.0 33.0
If there are two identical values listed 39.5 38.2 39.0 39.0 38.0 37.5 36.5 35.0 33.5
on the chart, select the steeper 39.5 38.4 39.5 39.0 38.5 37.5 37.0 35.5 33.5
pavilion angle. 40.0 38.6 39.5 39.5 38.5 38.0 37.0 35.5 34.0
40.0 38.8 40.0 39.5 39.0 38.0 37.5 36.0 34.0
Example: 40.5 39.0 40.5 40.0 39.5 38.5 37.5 36.0 34.5
• Visual pavilion depth: 41.0% 41.0 39.2 40.5 40.0 39.5 38.5 38.0 36.5 34.5
• Pavilion angle: 39.4° 41.0 39.4 41.0 40.5 40.0 39.0 38.0 36.5 35.0
41.5 39.6 41.0 40.5 40.0 39.5 38.5 37.0 35.0
3. Adjust your visual pavilion depth 41.5 39.8 41.5 41.0 40.5 39.5 38.5 37.0 35.5
estimate if there is a culet. In the row 42.0 40.0 41.5 41.5 40.5 40.0 39.0 37.5 35.5
that matches your pavilion angle 42.5 40.2 42.0 41.5 41.0 40.0 39.5 37.5 36.0
estimate, select the adjusted pavilion
42.5 40.4 42.5 42.0 41.5 40.5 39.5 38.0 36.0
depth that matches the culet size.
43.0 40.6 42.5 42.0 41.5 40.5 40.0 38.0 36.5

Example: 43.0 40.8 43.0 42.5 42.0 41.0 40.0 38.5 36.5
43.5 41.0 43.0 43.0 42.0 41.5 40.5 38.5 37.0
• Pavilion angle: 39.4°
44.0 41.2 43.5 43.0 42.5 41.5 40.5 39.0 37.0
• Culet Size: Medium
44.0 41.4 44.0 43.5 43.0 42.0 41.0 39.0 37.5
• Adjusted pavilion depth: 40.0%
44.5 41.6 44.0 43.5 43.0 42.0 41.5 39.5 37.5
44.5 41.8 44.5 44.0 43.5 42.5 41.5 40.0 38.0
45.0 42.0 45.0 44.5 43.5 43.0 42.0 40.0 38.5
45.5 42.2 45.0 44.5 44.0 43.0 42.0 40.5 38.5
45.5 42.4 45.5 45.0 44.5 43.5 42.5 40.5 39.0
46.0 42.6 45.5 45.5 44.5 43.5 43.0 41.0 39.0
46.5 42.8 46.0 45.5 45.0 44.0 43.0 41.0 39.5
46.5 43.0 46.5 46.0 45.0 44.5 43.5 41.5 39.5
47.0 43.2 46.5 46.0 45.5 44.5 43.5 42.0 40.0
47.5 43.4 47.0 46.5 46.0 45.0 44.0 42.0 40.0
47.5 43.6 47.5 47.0 46.0 45.0 44.5 42.5 40.5
48.0 43.8 47.5 47.0 46.5 45.5 44.5 42.5 41.0
48.5 44.0 48.0 47.5 47.0 46.0 45.0 43.0 41.0
48.5 44.2 48.5 48.0 47.0 46.0 45.0 43.5 41.5
49.0 44.4 48.5 48.0 47.5 46.5 45.5 43.5 41.5
49.5 44.6 49.0 48.5 48.0 47.0 46.0 44.0 42.0
49.5 44.8 49.5 49.0 48.0 47.0 46.0 44.0 42.0

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 DIAMOND GRADING LAB MANUAL

Effect on Cut Grade

Subtle pavilion angle differences can have a significant impact on the
diamond’s face-up appearance. Steep pavilion angles produce dark areas
under the diamond’s table. Shallow pavilion angles, in combination with
shallow crown angles and large tables, might produce unattractive patterns
like fisheyes.

John Koivula/GIA
This diamond’s deep pavilion makes the This diamond’s pavilion is so shallow
center of the diamond appear dark. This that you can see the diamond’s girdle
effect is called a nailhead. reflection just inside the table facet. This
effect is called a fisheye.

GIA CUT G RADE AND PAVILION ANGLE

This table lists the highest possible cut grade a diamond can receive based on its
pavilion angle. For example, a diamond with a pavilion angle of 40.4 degrees would
never qualify for excellent regardless of its other cut parameters.

Pavilion Angle Highest Possible Cut Grade*

<37.4° P

37.4° to 38.6° F

38.8° to 39.6° G

39.8° to 40.4° VG

40.6° to 41.8° EX

42.0° to 42.4° VG

42.6° to 43.0° G

43.2° to 44.0° F

>44.0° P

*The overall cut grade might be lower due to another grading parameter or combination of proportions.
< means less than > means greater than

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DIAMOND GRADING LAB MANUAL

Lower Half Length Percentage

Lower half length percentage is the length of a pair of lower half facets
expressed as a percentage of the girdle-to-culet distance. The average of eight
lower half length percentages is rounded to the nearest five percent (5%).

Lower half To visually estimate lower half length percentage:

facet length 1. Examine the diamond face-up and girdle-to-girdle, under magnifi-
cation, using darkfield illumination.
Girdle-to-culet distance
2. Consider the distance between the girdle and the culet as 100 percent.
3. Estimate the distance each lower half facet reaches toward the
culet. Start with one pair of lower half facets and move in a consis-
tent direction until you’ve examined all eight. Average your eight
estimates and round that figure to the nearest five percent (5%).

100% • Use the illustrations and descriptions below to help you estimate
0%
the percentage.
• If the appearance falls outside of, or between, these figures, you
will need to estimate an intermediate percentage.

55% 60% 65% 70%

75% 80% 85% 90%

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 DIAMOND GRADING LAB MANUAL

Effect on Cut Grade

Lower half facets that are very short or very long can have a negative effect
on a diamond’s face-up appearance, especially its pattern. Short lower half
facets tend to cause a blocky pattern while long lower half facets tend to
cause a splintery pattern especially in combination with a steep crown angle.

GIA CUT G RADE AND LOWER HALF LENGTH PERCENTAGE

This table lists the highest possible cut grade a diamond can receive based on its
lower half length percentage. For example, a diamond with a lower half length of 65
percent would never qualify for excellent regardless of its other cut parameters.

L.H. % Highest Possible Cut Grade*

<65% G

65% VG

70% to 85% EX

90% VG

>90% G

*The overall cut grade might be lower due to another grading parameter or combination of proportions.
< means less than > means greater than

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 DIAMOND GRADING LAB MANUAL

Average girdle diameter Girdle Thickness Percentage

Average Girdle thickness percentage is the average thickness of a diamond’s girdle,
girdle thickness measured at the eight bezel/main hill positions and expressed as a percentage
(hill position) of average girdle diameter. Girdle thickness percentage is rounded to the
nearest half of a percent (0.5%).

Bezel/main hill Upperl/lower half hill

Valley

On a round brilliant, the girdle consists of 16 narrow “valley” and 16 broader “hill”
positions. Girdle thickness percentage is measured at the hill positions located where
the bezel and main facets meet.

To estimate the diamond’s girdle thickness percentage:

1. Subtract crown height percentage and pavilion depth percentage
from the total depth percentage.
2. Round your result to the nearest half of a percent (0.5%), following
the rounding rules in the chart below.

Girdle Thickness % = total depth % — crown height % — pavilion depth %

Round to nearest 0.5%

G IRDLE THICKNESS PERCENTAGE ROUNDING R ULES

Use the following rules to round the value to the nearest 0.5%.

Percentage Rounding Example

x.0 to x.2 Round down to the nearest 0.0% 3.2 = 3.0%

3.3 = 3.5%
x.3 to x.7 Round up or down to the nearest 0.5%
3.7 = 3.5%

x.8 to x.9 Round up to the nearest 0.0% 3.8 = 4.0%

Example:
A round brilliant diamond has a total depth of 60.3%, a crown height of
14.5%, and a pavilion depth of 43.5%.
Girdle thickness % = 60.3 — 14.5 — 43.5 = 2.3%
= 2.5%

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 DIAMOND GRADING LAB MANUAL

Effect on Cut Grade

Girdle thickness affects the diamond’s weight ratio. Thicker girdles hide
unnecessary weight, so the thicker the girdle, the lower the cut grade.

GIA CUT G RADE AND G IRDLE THICKNESS PERCENTAGE

This table lists the highest possible cut grade a diamond can receive based on its girdle
thickness percentage. For example, a diamond with a girdle thickness of 5.0 percent
would never qualify for excellent regardless of its other cut parameters.
Grade limits for girdle thickness percentages less than 2.5 percent are determined
based on visual descriptions of the minimum and maximum valley areas.

Girdle Thickness % Highest Possible Cut Grade*

2.5 to 4.5% EX

5.0% to 5.5% VG

6.0% to 7.5% G

8.0% to 10.5% F

>10.5% P

*The overall cut grade might be lower due to another grading parameter or combination of proportions.
> means greater than

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DIAMOND GRADING LAB MANUAL

Girdle Thickness Description

Girdle thickness is assessed at the valley positions, as a range between the
thinnest (minimum) and the thickest (maximum) areas.

To visually evaluate girdle thickness:

1. Examine the diamond table-to-culet in profile view, under 10X
magnification using darkfield illumination.
2. Rotate the diamond to locate the minimum and maximum valley
positions.
3. Assign a girdle thickness range representing the minimum and
maximum valley positions (for example, THN to MED). When both
the minimum and maximum girdle thicknesses fall into the same
category (for example, MED), assign a single description.
• Use the illustrations and descriptions below to help you estimate
the thickness.
• Some additional considerations are listed on the next page.

Extremely thin (ETN): Very thin (VTN): Thin (THN): Medium (MED):
Knife-edge A very thin line at 10X A thin line at 10X Distinct at 10X

Slightly thick (STK): Thick (THK): Very thick (VTK): Extremely thick (ETK):
Obvious at 10X Very obvious at 10X Distracting at 10X Very distracting at 10X

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Special Case Guidelines for Girdle Thickness

You will need to consider these special case guidelines in your girdle
thickness assessment.
• An extremely thin girdle, often called a knife-edge, consists of an
area where the crown meets the pavilion with no apparent girdle
between them. You might need higher magnification to distinguish
between extremely thin and very thin.
• If a natural or extra facet thins the girdle, consider the remaining
area when determining thickness, even when it’s located at a hill
position. If only a knife-edge remains, call it extremely thin.
• When an indented natural, chip, or cavity breaks straight through
the girdle onto the crown and pavilion, disregard the girdle thick-
ness in that area.
• When an indented natural, chip, or cavity breaks only the crown or
only the pavilion, consider the remaining area when determining
thickness, even when it’s located at a hill position. If only a knife-
edge remains, call it extremely thin.

Gary Roskin
Two areas on this girdle are extremely An extra facet on the pavilion of this
thin. The girdle thickness range would diamond narrows the girdle at a hill posi-
be reported as extremely thin—at the tion. The thickness would be reported in a
location of the knife-edge—to slightly range from thin—at the location of the extra
thick. facet—to slightly thick—at the thickest
valley position.

Consider thickness in the

Ignore thickness in this area remaining area

The indented natural on the left breaks through both the crown and pavilion. There-
fore, you would not consider it when determining girdle thickness. The indented
natural on the right, however, breaks through on only the pavilion side, thinning the
girdle. In this case, the remaining portion of the girdle would be considered very thin.
Both indented naturals are considered when determining the diamond’s clarity grade.

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Effect on Cut Grade

The function of a diamond’s girdle is to prevent damage and also to provide
an edge for setting the stone into jewelry. Thinner girdles lower the cut grade
because they affect the diamond’s durability. Thicker girdles affect a
diamond’s weight ratio by hiding unnecessary weight. A girdle that is too
thin or too thick can cause setting problems.

GIA CUT G RADE AND G IRDLE THICKNESS

This table lists the highest possible cut grade a diamond can receive based on its minimum
and maximum girdle thickness.* For example, a diamond with a very thin to medium girdle
would never qualify for excellent regardless of its other cut parameters.
Maximum
ETN VTN THN MED STK THK VTK ETK

ETN G VG VG VG VG VG G F

VTN VG VG VG VG VG G F

THN EX EX EX VG G F
Minimum

MED EX EX VG G F

STK EX VG G F

THK VG G F

VTK G F

ETK F

*The overall cut grade might be lower due to another grading parameter or combination of proportions.

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Girdle Condition
The surface condition of a girdle is described as bruted, faceted, polished,
or lasered. Most round diamonds get their shapes during the bruting process.
This leaves the surface of the girdle with a frosty gray appearance. Often,
the cutter will add facets on the girdle or polish its surface. Sometimes, the
diamond outline is cut with a laser, leaving the girdle with minute parallel
grooves.

Examples:

Bruted Polished

Faceted Lasered

When the condition differs from what is necessary to create the diamond’s
shape—whether it’s faceted or polished—it is listed on the GIA Report for
descriptive purposes. If more than one girdle condition is present, the
description lists the condition that represents the majority of the girdle.

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Girdle Thickness Variations

When the angles between the upper and lower half facets are normal in
relation to the bezel and main facets, the facet junctions are distinct and the
girdle is nicely scalloped. The thicknesses at the hill positions where the
bezel and main facets meet are the same height as the hill position where
upper and lower half facet junctions meet.

Normal girdle

During the brillianteering stage, the cutter sometimes changes the orientation
of the upper and lower half facets in order to retain weight or remove clarity
characteristics. This is referred to as painting or digging out and results in
indistinct facet junctions and hill positions of differing thicknesses.

Painting
Painting refers to the tilting of upper or lower half facets toward the bezel
or main. Painting might be present on a diamond’s crown, pavilion, or both.
A painted diamond shows:
• Thinner hill positions where bezel and main facets meet.
• The more painting on the crown, the fainter the bezel facet junctions.
• The more painting on the pavilion, the fainter the main facet junctions.

Painting on the crown

Both by Eric Welch/GIA

This diamond has
significant painting
on both its crown
Painting on the pavilion and pavilion.

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Digging Out
Digging out is the opposite of painting. The cutter tilts the upper or lower
half facets, or both, away from the bezel or pavilion facets and toward each
other. Digging out might be present on a diamond’s crown, pavilion, or both.
A dug-out diamond shows:
• Thinner hill positions where upper and lower half facets meet.
• The more digging out on the crown, the fainter the upper half facet
junctions.
• The more digging out on the pavilion, the fainter the lower half
facet junctions.

Crown with digging out

Both by Eric Welch/GIA

This diamond has
significant digging
out on both its crown
Pavilion with digging out and pavilion.

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Visual Evaluation of Painting and Digging Out

Many optical measuring devices can measure the degree of painting and
digging out and account for their effect on the cut grade. The overall degree
of painting and digging out can also be assessed visually and described on
a relative scale from negligible to significant.

To visually assess painting and digging out:

1. Examine the diamond table-to-culet in profile view under 10X
magnification using darkfield illumination.
2. Compare the thickness at the bezel-to-main hill positions to the
thickness at upper-to-lower-half hill positions.
• If the thicknesses at all 16 hill positions are fairly equal, you would
describe the degree of painting and digging out as negligible.
3. If the thicknesses of the hill positions vary, assess the degree of
painting, digging out, or both, as negligible, moderate, significant,
or severe.
• Use the illustrations and descriptions on the next page to help
you estimate the degree of painting, digging out, or both.
• It is important to note that the diamond can have painting,
digging out, or both, on the crown only, the pavilion only, or on
both the crown and pavilion. For example, a diamond can be
dug-out on the crown and painted on the pavilion.
4. Consider the diamond’s face-up appearance. Both painting and
digging out produce distinctive and typically unattractive patterns,
especially when they are severe.

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Painting Examples:

Significant painting on the crown can Severe painting on the pavilion creates Diamonds with painting on both crown
produce dark radiating mains. a strong visual impact with broad, radi- and pavilion can display more extreme
ating, bright and dark areas. effects, with broad, radiating, bright and
dark areas.
Digging Out Examples:

All by Al Gilbertson and Barak Green/GIA

Severe digging out on the crown tends Digging out on the pavilion might Digging out on the both the crown and
to darken upper half facets and make produce an interrupted pattern and pavilion produces more extreme effects.
them appear to blend together. overall gray appearance. The center often appears dark, with a
bright broad band blending into a dark
band at the table edge.

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DIAMOND GRADING LAB MANUAL

Painting Examples and Descriptions

Equal painting on crown
and pavilion Painting on crown only Painting on pavilion only

Negligible Negligible Negligible

Moderate Moderate Moderate

Significant Significant Significant

Severe Severe Severe

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 DIAMOND GRADING LAB MANUAL

Digging Out Examples and Descriptions

Equal digging out on crown
and pavilion Digging out on crown only Digging out on pavilion only

Negligible Negligible Negligible

Moderate Moderate Moderate

Significant Significant Significant

Severe Severe Severe

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Effect on Cut Grade

Painting and digging out can affect the diamond’s weight ratio and face-up
appearance, especially its brightness and pattern. Both painting and digging
out are used to retain weight, especially if a small difference can lift a
diamond beyond an important weight such as the half-carat, one-carat, or
two-carat levels. As painting and digging out become more severe, so do
their impact on the cut grade.

GIA CUT G RADE AND G IRDLE THICKNESS VARIATIONS

This table lists the highest possible cut grade a diamond can receive based on the
overall degree of painting and digging out. For example, a diamond with moderate
painting, digging out, or both, would never qualify for excellent regardless of its other
cut parameters.
Painting or Digging Out Highest Possible Cut Grade*
Negligible EX

Moderate VG

Significant G

Severe F

*The overall cut grade might be lower due to another grading parameter or combination of proportions.

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Combined Effect of Proportions

Each proportion can limit the highest possible cut grade a diamond might
receive based on its own influence on the diamond’s face-up appearance or
design. The one that rates lowest frequently determines the grade. For
example, if all proportions fall within the allowable ranges for excellent but
one falls into the very good category, it lowers the grade to very good.
In your visual evaluation of face-up appearance, you might notice that the
diamond looks worse than its individual parameters suggest. If your
assessments are correct, this occurs when two or more proportions interact
in a negative way and lower the cut grade.
The interactions of the table percentage, crown angle, and pavilion angle are
especially critical. In general, diamonds with table percentage, crown angle,
and pavilion angle values that fall in the middle of their cut grade ranges
tend to stay in that grade. If one or more of these values falls near a grade
boundary, the cut grade tends to be one or two grades lower.

This diamond’s table

Excellent (EX) 58% percentage, crown
angle, and pavilion
angle are well within
52% minimum 62% maximum excellent ranges, so
TABLE % the diamond is solidly
33.5° in the excellent cut
grade.

31.5° minimum 36.5° maximum

CROWN ANGLE
41.2°

40.6° minimum 41.8° maximum

PAVILION ANGLE

This diamond’s table

Very Good (VG) 61%
percentage, crown
angle, and pavilion
angle are all close to
52% minimum 62% maximum the limits of the excel-
TABLE % lent cut grade range.
36.0° This combination
reduces brilliance and
fire enough to drop the
grade of this stone to
31.5° minimum 36.5° maximum very good.
CROWN ANGLE
41.6°

40.6° minimum 41.8° maximum

PAVILION ANGLE

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DIAMOND GRADING LAB MANUAL

Table Percentage, Crown Angle, and Pavilion Angle

As explained earlier, GIA Facetware® takes into account the combined effect
of the diamond’s proportions. If you are estimating a cut grade without
Facetware®, the tables below can help you determine if the interaction of
table percentage, crown angle, and pavilion angle lowers the grade.
The tables list the highest possible cut grade a stone can receive if it has a
particular combination of table size, crown angle, and pavilion angle. The
grades shown in these tables assume that the other cut parameters remain
constant. The default values for the other parameters are as follows:
• Star length percentage = 55%
• Lower half length percentage = 80%
• Girdle thickness percentage = 3.0%
• Girdle description = Thin to slightly thick
• Culet size = None, very small, or small
• Painting and digging out = Negligible
The cut grade might be lower for diamonds with different values for these
default parameters. This is especially true if the combination sits at a grade
boundary. In this case, you will need to use Facetware® to estimate the grade.
Table 47%–48%

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 DIAMOND GRADING LAB MANUAL

Table 49%–51%

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Table 52%–54%

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Table 55%–57%

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Table 58%–60%

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Table 61%–63%

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Table 64%–66%

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Table 67%–69%

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EVALUATING CRAFTSMANSHIP/FINISH
A polished diamond’s craftsmanship is the care that went into its final manu-
facturing steps, as indicated by its finish (polish and symmetry). Although
polish and symmetry might or might not affect the diamond’s face-up
appearance, they are considered part of the overall cut quality.

Polish
Polish is the quality of a diamond’s surface condition that results from the
polishing process, or from blemishes created after fashioning, often referred
to as wear and tear. Polish is rated on a relative scale from excellent to poor,
based on the visibility of its polish features at 10X magnification.

Polish Features
The following characteristics, when present, are considered in the polish
rating:

Both by Mitchell Moore/GIA

Pit (Pit): A minute opening that looks like Nick (Nck): A small notch on a facet
a tiny white dot at 10X. junction, usually along the girdle edge or
at the culet.

Vincent Cracco/GIA Mitchell Moore/GIA

Scratch (Scr): A thin, dull, white line Abrasion (Abr): A series of minute
across the surface. It might be curved or scratches or pits along a facet junction,
straight. producing a white or fuzzy appearance.

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 DIAMOND GRADING LAB MANUAL

Both by Mitchell Moore/GIA

Polish lines (TP, Wht): Fine parallel grooves left by the polishing process. They might
appear white (Wht) (left) or transparent (TP) (right). Heavy, transparent polish lines that
extend from a surface-reaching inclusion are referred to more specifically as drag lines.

Both by Mitchell Moore/GIA

Burn (Brn): Whitish haze across a facet, Dop burn (Dop): A more-specific term
or within a concentrated area, caused by for a surface burn resulting from exces-
exposure to excessive heat during sive heat at the location where the dop
polishing, or occasionally from a jeweler’s touches the diamond.
torch.

Mitchell Moore/GIA Vincent Cracco/GIA

Lizard skin (LS): Wavy or bumpy area Polish mark: A surface feature that
with a transparent, pitted texture; a result resembles an extra facet without a
of polishing almost parallel to the distinct or straight facet junction.
cleavage plane.

Mitchell Moore/GIA
Rough girdle (RG): Irregular pitted or Laser manufacturing remnant (LMR):
granular surface of a bruted girdle, Remains of laser cutting or marking left on
consisting of pits and nicks. the surface of a polished diamond. It affects
polish when it’s confined to the surface and
does not penetrate at 10X magnification.

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Determining Polish
The procedure for determining polish is very similar to the clarity-grading
procedure. Because of this, graders usually evaluate clarity and polish at the
same time.

To determine polish:
1. Using tweezers, examine the diamond girdle-to-girdle and face-up.
To get an initial impression of the polish, examine the diamond in the
microscope under 10X magnification and darkfield illumination.
2. Examine the diamond table-to-culet, one section at a time, to locate
and identify the polish features present in the diamond. Use the
same grading methodology you used for clarity grading.

1 2

Both by Denise Conrad/GIA

3. If you find polish features, examine the diamond face-up and girdle-
to-girdle, under 10X in both the microscope and the loupe. This time,
view the diamond in at least four different positions. Different orienta-
tions might cause some features to be more or less apparent.

3 x
x

x
x
Denise Conrad/GIA

4. Assign a polish rating of excellent, very good, good, fair, or poor.

Consider the diamond’s overall face-up appearance as well as pol-
ish features seen in any view. Emphasis is placed on the diamond’s
face-up appearance with a 10X loupe.
• Use the polish-rating guidelines on the next page to help you de-
termine the rating.
• When they’re severe, consider polish features located on the gir-
dle in your assessment.
• Consider reflections of polish features in your assessment when
they are visible face-up at 10X.

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POLISH-RATING G UIDELINES
This table describes the visual appearance of polish features at 10X magnification for each
category.
Rating and Overall Impression Example*

Very faint scratch

Excellent (EX): ranges from no
polish features to a few minute
features that can be viewed with
difficulty face-up at 10X
magnification.

Transparent polish
lines
Very Good (VG): minor polish
features seen face-up at 10X
magnification.

White polish lines

Good (G): noticeable polish
features seen face-up at 10X
magnification. Might affect the
diamond’s luster when viewed with
the unaided eye.

Burn on pavilion
Fair (F): obvious heavy polish
features seen face-up at 10X
magnification. Affect the diamond’s
luster when viewed with the unaided
eye.

Extensive burn on
crown and pavilion
Poor (P): prominent heavy polish
features seen face-up at 10X
magnification. Significantly affect the
diamond’s luster when viewed with
the unaided eye.

*Some features were enlarged for the purpose of illustration; it is the appearance at 10X that is considered during evalua-
tion. Note, too, that each category encompasses a range of appearances and that the selected examples do not represent
the highest or lowest points within their categories.

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DIAMOND GRADING LAB MANUAL

Effect on Cut Grade

A diamond’s polish rating can limit its highest possible cut grade. With the
exception of poor, a one-grade difference between the diamond’s polish
rating and the other aspects of cut does not further affect the diamond’s face-
up appearance, and these differences cannot be reliably detected with the
unaided eye.

GIA CUT G RADE AND POLISH

This table lists the highest possible cut grade a diamond can receive based on its
polish rating. For example, a diamond with a polish rating of good would never qualify
for excellent regardless of its other cut parameters.

Polish Rating Highest Possible Cut Grade*

Excellent
EX
Very Good

Good VG

Fair G

Poor P

*The overall cut grade might be lower due to another grading parameter or combination of proportions.

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Symmetry
Symmetry refers to the exactness of a diamond’s shape, and to the
symmetrical arrangement and even placement of its facets. Symmetry is
rated on a relative scale, ranging from excellent to poor, based on the
visibility of symmetry variations at 10X magnification.

A round brilliant diamond should have a symmetrical round girdle outline (left). Also,
the proportions and facets on each section of the round brilliant should match (center
and right). A round brilliant has eight sections, each consisting of a bezel facet, a main
facet, and two bordering half facets.

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Symmetry Variations
The following variations, when present, are considered in the symmetry
rating. The presence of one variation often leads to other variations. For
example, variation in the diamond’s crown angles often results in a table
that is not centered or misshapen facets, or both.

Out-of-round (OR): The girdle outline is not perfectly round.

A difference between the

minimum and maximum
girdle diameters can help
detect a lack of roundness
(left). A natural, an extra
facet, or irregular girdle
faceting might cause a flat-
tened area. This is referred
to as an uneven outline
(UO) (right).

Table off-center (T/oc): The table facet is not centered in the crown.

A bezel facet will appear

longer than the bezel on
the opposite side. Looking
through the table, you will
see more of the pavilion on
one side of the culet (left).
Table off-center is typically
related to uneven crown
angles (right).

Culet off-center (C/oc): The culet is not centered in the pavilion.

The cross-line formed by

the lower half facets will
appear bowed. Looking
through the table, you will
see more of the pavilion on
one side of the culet (left).
Culet off-center is typically
related to uneven pavilion
angles (right).

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Table/culet alignment (T/C): The table and culet are displaced in oppo-
site directions.
You will see visual indica-
tions of an off-center table
and culet in the same
diamond (left). In profile
view, the table and culet
will appear displaced in
opposite directions (right).

Non-octagonal table (T/oct): The table facet is not a regular octagon,

meaning it does not have eight equal sides or angles. Variation in the
diamond’s table measurements can indicate the presence of this feature.

The sides of the table will

be unequal in length, or
opposing facet junctions
will not be parallel. The
star facets, and possibly
the bezels, will appear
misshapen.

Crown height variation (CHV): Variation in the diamond’s eight crown

height measurements.

Crown height variation

affects the girdle. Either the
table and girdle are not
parallel (left), or there is a
thinned girdle area at a
bezel position (right). When
you view the diamond face-
up, the bezels might
appear misshapen.

Pavilion depth variation (PDV): Variation in the diamond’s eight

pavilion depth measurements.
Pavilion depth variation
affects the girdle. Either the
table and girdle are not
parallel (left), or there is a
thinned girdle area at a
main position (right). In the
face-up view, the mains
might appear misshapen.

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Crown angle variation (CV): Variation in the diamond’s eight measured

crown angles.

With crown angle variation,

the table might be off-
center (left). If the table is
centered, crown angle vari-
ation affects the girdle
(right). In the face-up view,
the bezels might appear
misshapen.

Pavilion angle variation (PV): Variation in the diamond’s eight meas-

ured pavilion angles.

If there is pavilion angle

variation, the culet might be
off-center (left). If the culet
is centered, pavilion angle
variation affects the girdle
(right). In the face-up view,
the mains might appear
misshapen.

Girdle thickness variation (GTV): Variations in girdle thickness at the

eight bezel-to-main hill positions.

Star angle variation (SV): Unequal star facet angles.

The height of the star

facets from the table to the
bezel point will vary. In the
face-up view, star facets—
and possibly bezel
facets—will appear
misshapen.

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 DIAMOND GRADING LAB MANUAL

Star percentage variation (SPV): Variation in the diamond’s eight meas-

ured star facet length percentages.

Star facets will appear

misshapen. Also, bezel
facets might appear
misshapen.

Upper half variation (UHV): Unequal upper half facet angles.

This characteristic affects

the thickness of the girdle
where the upper half facets
meet. In the face-up view,
the bezels might appear
misshapen.

Lower half percentage variation (LPV): Variation in the diamond’s

eight measured lower half facet length percentages.

The lower half facets and

main facets will appear
misshapen.

Lower half variation (LHV): Unequal lower half facet angles.

Affects the thickness of the

girdle where the lower half
facets meet. In the face-up
view, the mains might
appear misshapen.

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Misalignment (Aln): Displacement of the crown and pavilion facets in

relation to each other.

Either the points of the

bezel and main facets do
not align across the girdle,
or the facet junctions of the
upper and lower half facets
do not align.

Misshapen facet (Fac): A facet that is a different shape or size than other
facets of the same type, or distortion of a given facet. On a brilliant cut,
they are referred to more specifically as misshapen bezel (MB),
misshapen star (MS), or misshapen main (MM). These are most often the
result of a proportion-related variation. They might also be the result of
the adjustments made during brillianteering to realign crown and pavilion
faceting (referred to as twist).

MB MM

MS

This image shows crown twist. The table This image shows pavilion twist. The
is octagonal and centered but it is culet is centered but there are
rotated, resulting in misshapen stars misshapen mains (MM). The cross-lines
(MS) and misshapen bezels (MB). formed by the lower half facets are bent.

Non-pointing (Ptg): Adjoining facets do not meet at precise points, or a

facet is not at its prescribed location. A bezel or main facet that does not
reach its prescribed location is referred to more specifically as a short
bezel (SB), open bezel (OB), short main (SM), or open main (OM).

SB OM

OB SM

Ptg Ptg

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Missing facet (MF): Asymmetrically missing facet.

A single missing facet

would result in a symmetry
rating of good or fair,
depending on its size and
location. A missing main,
for example, would result in
a fair rating.

Extra facet (EF): An additional facet placed without regard for symmetry
and not required by the cutting style.

Extra facets might result in

short facets, misshapen
facets, or non-pointing. An
extra facet located at the
girdle can create a flat-
tened area, affecting the
diamond’s roundness.

Natural (N): A portion of the original surface, or skin, of a rough

diamond left on a fashioned stone.

Naturals might result in

short facets, misshapen
facets, or non-pointing. A
natural located at the girdle
can create a flattened area,
affecting the diamond’s
roundness.

NOTE:
You can use an optical measuring device to measure some of these sym-
metry variations. The GIA Laboratory uses a combination of measured sym-
metry parameters and visual assessments to determine the symmetry
grade. Additional software for analyzing symmetry is also available to the
trade for use with most optical measuring devices. Visual assessment is
still required to account for variations that cannot be measured, and in
cases where the combination of symmetry variations lowers the rating.

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Determining Symmetry
To determine symmetry:
1. To get an initial impression of symmetry, hold the diamond in
tweezers and examine it in the microscope, face-up and girdle-to-
girdle, under 10X magnification with darkfield illumination.
• Is the outline round?
• Are the table and culet centered?
• Are like facets symmetrically sized and shaped?
2. Hold the diamond table-to-culet in profile view. Rotate the diamond to
find and identify any variations that are best seen in that position.
• Are the various facet angles equal?
• Are there variations in the girdle?
• Are crown and pavilion facets aligned?

1 2

Both by Denise Conrad/GIA

3. If you see symmetry variations, examine the diamond in the micro-

scope and the loupe at 10X, in the face-up, girdle-to-girdle orienta-
tion. This time, view the diamond in at least four different
positions. Some features become more or less apparent when you
change the diamond’s orientation.

3
x
x

x
x
Denise Conrad/GIA

4. Assign a symmetry rating of excellent, very good, good, fair, or poor.

Consider the diamond’s overall face-up appearance as well as symme-
try variations seen in any view. Place emphasis on the diamond’s face-
up appearance with a 10X loupe. Use the symmetry-rating guidelines
on the next page to help you determine the rating.

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 DIAMOND GRADING LAB MANUAL

SYMMETRY-RATING G UIDELINES
This table describes the visual appearance of symmetry variations at 10X magnification
for each rating category.
Rating and Overall Impression Example*

Misalignment

Excellent (EX): ranges from no

symmetry variations to a few minute
features that can be viewed with
difficulty at 10X magnification.

Misalignment and
lower half percentage
variation
Very Good (VG): minor symmetry
variations seen at 10X magnification.

Culet off-center
Good (G): noticeable symmetry
variations seen at 10X magnification.
Might affect the diamond’s overall
appearance when viewed with the
unaided eye.

Non-octagonal table
Fair (F): obvious symmetry variations
seen at 10X magnification. Often
affect the diamond’s overall
appearance when viewed with the
unaided eye.

Out-of-round
Poor (P): prominent symmetry
variations seen at 10X magnification.
Significantly affect the diamond’s
overall appearance when viewed with
the unaided eye.

*Some features were enlarged for the purpose of illustration; it is the appearance at 10X that is considered during evalua-
tion. Note, too, that each category encompasses a range of appearances and the selected examples do not represent the
highest or lowest points of their categories.

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DIAMOND GRADING LAB MANUAL

Effect on Cut Grade

A diamond’s symmetry rating can limit the highest possible cut grade it
might receive. With the exception of poor, a one-grade difference between
the diamond’s symmetry rating and the other cut aspects has no further effect
on the diamond’s face-up appearance. In general, these differences cannot
be reliably discerned with the unaided eye.

GIA CUT G RADE AND SYMMETRY

This table lists the highest possible cut grade a diamond can receive based on its
symmetry rating. For example, a diamond with a symmetry rating of good would never
qualify for excellent regardless of its other cut parameters.

Symmetry Rating Highest Possible Cut Grade*

Excellent
EX
Very Good

Good VG

Fair G

Poor P

*The overall cut grade might be lower due to another grading parameter or combination of proportions.

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 DIAMOND GRADING LAB MANUAL

ESTIMATING THE CUT GRADE

You can estimate the cut grade of a round brilliant diamond by using:
• An optical measuring device along with GIA Facetware®
Cut Estimator software.
• The online GIA Facetware® Cut Estimator software.
• Visual estimation methods and limiting factor tables included in
Eric Welch/GIA
this manual.

Optical Measuring Device with GIA Facetware®

An optical measuring device with GIA Facetware® installed measures the
diamond, determines proportion averages, and calculates a cut grade that
includes the effect on the diamond’s brightness, fire, pattern, and weight
ratio. Most devices also measure and take into account the effects of painting
and digging out. Additional software can be installed to evaluate the
symmetry variations that can be measured. Denise Conrad/GIA

If you use an optical measuring device, you will need to take into account Using an optical measuring device with
parameters that cannot be measured but might lower the grade. These GIA Facetware® software is the most
accurate method for determining the cut
include: grade (top). You will still need to perform
visual assessments of parameters that
• Culet size can’t be measured (bottom).
• Girdle thickness description
• Polish
• Symmetry

NOTE:
Your results might differ from those on a GIA Report if your measured val-
ues or visual assessments differ from those determined by the laboratory.
In order to obtain accurate results, measuring devices must be routinely
calibrated and maintained. Also, values at a grade border can vary due to
rounding and the tolerance of the device.

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DIAMOND GRADING LAB MANUAL

Online GIA Facetware® Cut Estimator

Software
The GIA Facetware® Cut Estimator software predicts the GIA Cut Grade
using the same proportion calculations and limiting factors as the GIA Labo-
ratory. It also allows the comparison of multiple sets of proportions at the
same time, which is helpful for manufacturers in cut planning. The software
is available free of charge in web and mobile versions.

To use GIA Facetware® Cut Estimator:

1. Determine the following proportions using measured or estimated
results and enter them into Facetware:
• Table percentage
• Crown angle
• Pavilion angle
• Star length percentage
• Lower half length percentage
• Girdle thickness percentage
You don’t need to enter crown height, pavilion depth, or total depth.
These are calculated based on the other entered proportions. The calcu-
lated values might differ from the measured values listed on the report,
but this will not impact the grade.

2. Visually evaluate these additional parameters and enter them into

Facetware:
• Girdle thickness description (min and max)
• Culet size
• Polish
• Symmetry
• Painting and digging out
3. The software will calculate the estimated GIA Cut Grade.

NOTE:
Your result might differ from that on a GIA Report if the entered values differ
from those determined by the laboratory.

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 DIAMOND GRADING LAB MANUAL

Visual Estimation Techniques and Look-up

Tables
If you do not have access to an optical measuring device or the GIA Facetware®
Cut Estimator software, you can estimate the cut grade using visual estimation
methods and limiting-factor tables found in this manual.
It is important to note that a quick assessment of just the diamond’s brightness,
fire, pattern, overweight percentage, and total depth can give you a good idea
of the overall cut quality. This is helpful when you need to make a quick
judgment of a diamond’s quality, such as in a buying situation.

To estimate the cut grade:

1. Visually evaluate the diamond’s face-up appearance of brightness,
pattern, and fire.
2. Evaluate the diamond’s proportions and design.
• Calculate the diamond’s overweight and total depth percentages
and determine their individual effects on the cut grade.
• Estimate the diamond’s proportions and determine their individ-
ual effects on the cut grade:
Table percentage
Star length percentage
Crown angle
Crown height percentage
Culet size
Pavilion angle
Lower half length percentage
Girdle thickness percentage
Girdle thickness description (min to max)
Painting and digging out
• Evaluate the combined effect of table percentage, crown angle,
and pavilion angle on the cut grade using the tables provided
earlier in this section.
3. Evaluate the diamond’s polish and symmetry and their individual
effects on the cut grade.
4. Compare the lowest result you obtained for face-up appearance
(step 1) to the lowest result you obtained for proportions and design
(step 2). If these differ by more than one grade, there is a chance NOTE:
that either your evaluation of face-up appearance or one or more of
Your result might differ from that
your estimated proportions are incorrect. In this case, recheck your on a GIA Report if the entered
results. values differ from those determined
5. Assign an overall cut grade that is equal to the lowest result for by the laboratory.
each of these parameters.
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DIAMOND GRADING LAB MANUAL

CUT G RADE R EFERENCE CHART

This table lists the parameter ranges for each GIA cut grade. The ranges overlap, and the number of possibilities
increases at each lower cut-grade level. When one parameter falls outside the range of a particular cut grade into the
level below, the lower level automatically becomes the highest possible cut grade for that diamond.
Remember that the GIA Cut Grading System considers a round brilliant diamond’s proportions together as well as
individually. Even if all of a diamond’s parameters are within the limits for a particular grade, it might receive a lower
cut grade when the parameters interact in a negative way to lessen a diamond’s appearance.

Excellent Very Good

Brightness Very bright Bright

Pattern No pattern defects to minute Minor pattern defects; slight

pattern defects; even pattern of darkening of mains and along upper
bright and dark areas with strong half facets
contrast; symmetrical pattern of
dark radiating mains permitted
within the table if the area around
the culet remains bright
Fire High High to moderate
Overweight % Up to 9% Up to 16%
Total Depth % 57.5% to 63.0% 56.0% to 64.5%
Table % 52% to 62% 50% to 66%
Star Length % 45% to 65% 40% to 70%
Crown Angle 31.5° to 36.5° 26.5° to 38.5°
Crown Height % 12.5% to 17.0% 10.5% to 18.0%
Culet Size None to small None to medium
Pavilion Angle 40.6° to 41.8° 39.8° to 42.4°
Lower Half Length % 70% to 85% 65% to 90%
Girdle Thickness % 2.5% to 4.5% Up to 5.5%
Girdle Thickness Description THN to STK VTN to THK
Painting and Digging Out Negligible Negligible to Moderate
Polish Excellent to Very Good Excellent to Good
Symmetry Excellent to Very Good Excellent to Good
Combined Effect of Proportions Proportions within the Excellent Proportions within the Very Good
range might combine to negatively range might combine to negatively
affect the appearance and lower affect the appearance and lower
the grade. the grade.

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 DIAMOND GRADING LAB MANUAL

Good Fair Poor

Presence of some dark areas Stone appears generally dark, with Stone appears very dark, with few
detracts from stone’s appearance some bright areas bright areas
Noticeable pattern defects; dark Obvious pattern defects; fisheye Prominent pattern defects; very
mains extend under the crown gives general “grayed-out” dark areas under the table
facets and distract from appearance; lack of contrast (nailhead); very dark upper half
appearance; slight dark ring within between light and dark areas; very facets; extremely dark mains;
the table; somewhat dark upper half dark upper half facets; general pattern lacks contrast and might
facets darkness under the table; very dark appear very “blocky”
radiating mains
Moderate Moderate to low Low; very little visible fire
Up to 25% Any value Any value
53.0% to 66.5% 51.0% to 70.9% <51.0% to >70.9%
47% to 69% 44% to 72% <44% to >72%
Any value Any value Any value
22.0° to 40.0° 20.0° to 41.5° <20.0° to >41.5°
9.0% to 19.5% 7.0% to 21.0% <7.0% to >21.0%
None to large Very large Extremely large
38.8° to 43.0° 37.4° to 44.0° <37.4° to >44.0°
Any value Any value Any value
Up to 7.5% Up to 10.5% Any value
ETN to VTK ETN to ETK ETN to ETK
Negligible to Significant Negligible to Severe Negligible to Severe
Excellent to Fair Excellent to Fair Excellent to Poor
Excellent to Fair Excellent to Fair Excellent to Poor
Proportions within the Good range Proportions within the Fair range
might combine to negatively affect might combine to negatively affect
the appearance and lower the the appearance and lower the
grade. grade.

< means less than > means greater than

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DIAMOND GRADING LAB MANUAL

CUT GRADE EXAMPLES Table size: 53%

Crown angle: 34.5°
The following pages contain examples of the Pavilion angle: 40.8°
five GIA cut grades. The virtual-diamond Star length: 55%
Lower half length: 80%
images show the face-up static patterns Girdle thickness: 2.5%
associated with appearance for each of the (Medium)
Culet size: None
five grades, as seen under identical lighting Total depth: 62.5%
Polish: VG
and viewing conditions. They are best under- Symmetry: EX
stood when they are seen as the diamond is Pavilion depth: 43.0%
Crown height: 16.0%
rocked or tilted.
An even distribution of
bright and dark patterns
typifies the best looking
diamonds. Here, the pavilion
main facets reflect dark, but
the areas surrounding them
Excellent Cut Grade are bright.

Table size: 57% Table size: 57%

Crown angle: 35.5° Crown angle: 32.0°
Pavilion angle: 40.8° Pavilion angle: 41.6°
Star length: 55% Star length: 55%
Lower half length: 80% Lower half length: 80%
Girdle thickness: 3.0% Girdle thickness: 2.5%
(Medium) (Slightly Thin to Medium)
Culet size: None Culet size: None
Total depth: 61.2% Total depth: 60.5%
Polish: EX Polish: VG
Symmetry: VG Symmetry: EX
Pavilion depth: 43.0% Pavilion depth: 44.5%
Crown height: 15.5% Crown height: 13.5%

An even distribution of bright An even distribution of

and dark patterns typifies the bright and dark patterns
best looking diamonds. The typifies the best looking
balanced even reflection diamonds. The balanced
pattern is more visible when even reflection pattern is
the diamond is in movement. more visible when the
diamond is in movement.

Table size: 59% Table size: 61%

Crown angle: 35.0° Crown angle: 33.0°
Pavilion angle: 41.0° Pavilion angle: 41.2°
Star length: 55% Star length: 55%
Lower half length: 80% Lower half length: 80%
Girdle thickness: 3.5% Girdle thickness: 2.5%
(Medium) (Medium)
Culet size: None Culet size: None
Total depth: 61.2% Total depth: 59.2%
Polish: EX Polish: VG
Symmetry: EX Symmetry: EX
Pavilion depth: 43.5% Pavilion depth: 43.5%
Crown height: 14.5% Crown height: 12.5%

An even distribution of Diamonds with large table

bright and dark patterns facets only have a few
typifies the best looking proportion combinations that
diamonds. The balanced contribute to an appearance
even reflection pattern is that qualifies them for the
more visible when the Excellent cut grade.
diamond is in movement.

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 DIAMOND GRADING LAB MANUAL

Table size: 53%

Crown angle: 34.5°
Pavilion angle: 40.8°
Star length: 55%
Lower half length: 80%
Girdle thickness: 4.5%
(Slightly Thick to Thick)
Culet size: Medium
Total depth: 64.2%
Polish: VG
Symmetry: EX
Pavilion depth: 43.0%
Crown height: 16.0%

All parameters are within the

Excellent range except total
depth, girdle thickness, and
culet size. The face-up appear -
ance may be as good as those
in the Excellent range, but the
Very Good Cut Grade diamond has too much weight
for its diameter.

Table size: 53% Table size: 57%

Crown angle: 30.0° Crown angle: 29.0°
Pavilion angle: 41.4° Pavilion angle: 41.8°
Star length: 55% Star length: 55%
Lower half length: 80% Lower half length: 80%
Girdle thickness: 3.5% Girdle thickness: 2.5%
(Medium) (Thin to Medium)
Culet size: None Culet size: None
Total depth: 60.9% Total depth: 59.8%
Polish: VG Polish: VG
Symmetry: VG Symmetry: EX
Pavilion depth: 44.0% Pavilion depth: 44.5%
Crown height: 13.5% Crown height: 12.0%

A shallower crown angle While a shallower crown angle

tends to darken the overall darkens the overall appearance
appearance of the diamond. of a diamond, the larger table
The pattern of darker opens the diamond up, brighten-
reflected main facets is ing it, but altering the reflection
somewhat prominent. pattern from that created by a
smaller table (see above).

Table size: 57% Table size: 61%

Crown angle: 37.5° Crown angle: 31.0°
Pavilion angle: 40.2° Pavilion angle: 41.4°
Star length: 55% Star length: 55%
Lower half length: 80% Lower half length: 80%
Girdle thickness: 3.5% Girdle thickness: 3.5%
(Medium) (Medium)
Culet size: None Culet size: None
Total depth: 62.2% Total depth: 59.0%
Polish: VG Polish: VG
Symmetry: VG Symmetry: VG
Pavilion depth: 42.0% Pavilion depth: 44.0%
Crown height: 16.5% Crown height: 11.5%

Producing a pattern of The slightly shallower crown

darkened main facet reflec - angle (compared to the
tions with a steeper crown Excellent image, previous page,
angle is accomplished by bottom right) contributes to a
lowering the pavilion angle. slight overall darkening of the
The overall result is a slight diamond’s appearance.
darkening of the diamond’s
general appearance.

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DIAMOND GRADING LAB MANUAL

Table size: 53%

Crown angle: 32.0°
Pavilion angle: 42.8°
Star length: 55%
Lower half length: 80%
Girdle thickness: 3.5%
(Medium)
Culet size: None
Total depth: 64.2%
Polish: VG
Symmetry: EX
Pavilion depth: 46.5%
Crown height: 14.5%

While this diamond is some-

what bright, it lacks a strong
or distinct reflection pattern.

Good Cut Grade

Table size: 57% Table size: 57%
Crown angle: 33.5° Crown angle: 33.5°
Pavilion angle: 39.6° Pavilion angle: 42.8°
Star length: 55% Star length: 55%
Lower half length: 80% Lower half length: 80%
Girdle thickness: 3.0% Girdle thickness: 3.5%
(Medium) (Medium to Slightly Thick)
Culet size: None Culet size: None
Total depth: 58.8% Total depth: 63.8%
Polish: VG Polish: VG
Symmetry: EX Symmetry: EX
Pavilion depth: 41.5% Pavilion depth: 46.5%
Crown height: 14.0% Crown height: 14.0%

The shallower pavilion angle This diamond lacks a strong

contributes to the darker or distinct reflection pattern.
reflection pattern seen in
this diamond.

Table size: 61% Table size: 61%

Crown angle: 33.5° Crown angle: 31.0°
Pavilion angle: 39.6° Pavilion angle: 41.4°
Star length: 55% Star length: 55%
Lower half length: 80% Lower half length: 80%
Girdle thickness: 3.0% Girdle thickness: 3.5%
(Medium) (Medium)
Culet size: None Culet size: None
Total depth: 57.5% Total depth: 60.0%
Polish: G Polish: VG
Symmetry: EX Symmetry: VG
Pavilion depth: 41.0% Pavilion depth: 44.0%
Crown height: 13.0% Crown height: 11.5%

The shallow pavilion angle The grade is lowered due to

darkens this diamond, digging out on the pavilion
creating a strong, dark which radically changes the
reflection pattern. face-up view of the diamond
on the left, changing its
pattern and darkening its
appearance.

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 DIAMOND GRADING LAB MANUAL

Table size: 53%

Crown angle: 30.0°
Pavilion angle: 39.4°
Star length: 55%
Lower half length: 80%
Girdle thickness: 5.5%
(Thick)
Culet size: None
Total depth: 59.8%
Polish: VG
Symmetry: VG
Pavilion depth: 41.0%
Crown height: 13.5%

The overall dark appearance

is a result of the shallow
pavilion and crown angles.

Fair Cut Grade

Table size: 57% Table size: 57%
Crown angle: 24.0° Crown angle: 40.0°
Pavilion angle: 40.2° Pavilion angle: 43.0°
Star length: 55% Star length: 50%
Lower half length: 85% Lower half length: 70%
Girdle thickness: 3.0% Girdle thickness: 2.5%
(Medium) (Thin)
Culet size: None Culet size: None
Total depth: 54.8% Total depth: 68.2%
Polish: VG Polish: VG
Symmetry: G Symmetry: G
Pavilion depth: 42.0% Pavilion depth: 46.5%
Crown height: 9.5% Crown height: 18.0%

The extremely shallow crown This diamond lacks life and

angle is a major cause of the is quite unattractive, a result
darkness seen under the of the steep crown and
table in this diamond. The pavilion angles. The
culet is off-center. diamond is also slightly out
of round.

Table size: 57% Table size: 61%

Crown angle: 33.5° Crown angle: 26.0°
Pavilion angle: 42.8° Pavilion angle: 39.8°
Star length: 55% Star length: 45%
Lower half length: 70% Lower half length: 85%
Girdle thickness: 8.0% Girdle thickness: 4.0%
(Extremely Thick) (Slightly Thick)
Culet size: None Culet size: None
Total depth: 68.5% Total depth: 55.2%
Polish: VG Polish: VG
Symmetry: F Symmetry: G
Pavilion depth: 46.5% Pavilion depth: 41.5%
Crown height: 14.0% Crown height: 9.5%

While the general The shallow crown and

proportions would cause pavilion angles are the
this diamond to fall into the primary cause of the overall
Good range (even though it darkness in this diamond.
is out-of-round and the culet The culet is also slightly off-
is off-center), the extremely center.
thick girdle lowers the
diamond into the Fair range.

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DIAMOND GRADING LAB MANUAL

Table size: 48%

Crown angle: 39.0°
Pavilion angle: 42.0°
Star length: 55%
Lower half length: 80%
Girdle thickness: 5.5%
(Thick)
Culet size: None
Total depth: 71.3%
Polish: G
Symmetry: VG
Pavilion depth: 45.0%
Crown height: 21.0%

The unusual face-up pattern

(culet reflections seen in the
main facets) is a result of
the extreme crown angle
and small table size. The
culet is also off-center.
Poor Cut Grade
Table size: 50% Table size: 57%
Crown angle: 40.0° Crown angle: 40.0°
Pavilion angle: 41.0° Pavilion angle: 43.0°
Star length: 55% Star length: 55%
Lower half length: 70% Lower half length: 75%
Girdle thickness: 5.5% Girdle thickness: 5.5%
(Thick) (Thick)
Culet size: None Culet size: None
Total depth: 69.7% Total depth: 69.8%
Polish: G Polish: G
Symmetry: VG Symmetry: F
Pavilion depth: 43.5% Pavilion depth: 46.5%
Crown height: 21.0% Crown height: 12.5%

Although proportions are The steep crown angle and

similar to the diamond other proportions would
above, the shorter lower cause this to be Fair, except
half facets cause a dramatic that this diamond has
difference in appearance. extreme digging on the
pavilion, the culet is off-
center and the diamond is
slightly out-of-round.

Table size: 57% Table size: 60%

Crown angle: 41.0° Crown angle: 41.5°
Pavilion angle: 44.0° Pavilion angle: 43.4°
Star length: 55% Star length: 65%
Lower half length: 80% Lower half length: 85%
Girdle thickness: 5.5% Girdle thickness: 5.0%
(Thick) (Slightly Thick to Thick)
Culet size: None Culet size: None
Total depth: 72.2% Total depth: 70.2%
Polish: G Polish: G
Symmetry: F Symmetry: G
Pavilion depth: 48.5% Pavilion depth: 47.5%
Crown height: 12.5% Crown height: 17.5%

The steep pavilion angle The steep crown angle,

and crown angle create a pavilion angle, and large
dark appearance. The culet star facets combine to make
is also off-center. a dark center and unusual
pattern in this diamond.

182
COLOR G RADING 183
D-to-Z Color Grading 183
Masterstones 184
Masterstone Selection Criteria 184
Partial Master Sets 185
Synthetic Cubic Zirconia Master Sets 185
Masterstone Set-up 186
Viewing Environment 187
Viewing Geometry 188
Color Grading Procedure 190
Master-eye Effect 192
Using a Partial Master Set 193
Grading Colors Other than Yellow 194
Brown Diamonds 194
Gray Diamonds 194
Other Colors 194
Special Case Guidelines 196
Significant Size Differences 196
Heavily Included Diamonds 196
Estimating Color Grades 197
Fluorescence 199
Determining Fluorescence 200
Colored Diamond Color Grading 202
Color Descriptions and Grades 202
Fancy Color Grades (Tone and Saturation) 202
Color Descriptions (Hue) 204
Black and White Diamonds 205
Color Distribution 206
Colored Diamond Grading Process 206
Viewing Environment 206
Viewing Geometry 207
Characteristic Color 208

COLOR GRADING
Color Comparison Methodology in the Lab 209
COLOR G RADING
Diamonds come in a wide range of colors, from colorless through near-
colorless and even colors like blue and red. Since diamond color has a lot
to do with a diamond’s overall quality, it’s important to practice the color-
grading skills you’ll learn in this section.

D-TO-Z COLOR GRADING

The GIA D-to-Z Color Grading System assesses the presence or absence of
color in the most commonly occurring colorless to light yellow, light brown,
and light gray diamonds.
The scale used to grade color begins with D (colorless) and continues
through letter grades that indicate an increase in the amount of color, ending
with Z. Each letter grade represents a narrow range of color, not a specific
point, so two diamonds with the same color grade can actually differ slightly
in their depth of color.
The levels of the GIA Color Scale are divided into colorless, near-colorless,
faint, very light, and light ranges.

Colorless Near-colorless Faint Very light Light

Robert Weldon/GIA
The GIA Color Scale (right) is divided into colorless, near-colorless, faint, very light,
and light ranges, as illustrated by the examples above.

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DIAMOND GRADING LAB MANUAL

Masterstones
The D-to-Z color-grading process involves the use of Master Color
Comparison Diamonds (also known as “masters” or “masterstones”). Each
masterstone has a known position on the grading scale, and designates the
least amount of color in that grade range. For example, a G master designates
the least amount of color in the G color-grade range.
The GIA Laboratory uses a complete set, with a masterstone located at each
letter-grade designation. The grading process involves a visual comparison
of the masterstones with the diamond being graded.

Masterstone Selection Criteria

Masterstones are graded by the GIA Laboratory. Each one, in addition to its
specific place on the D-to-Z scale, must meet the following criteria:
• Must be a round brilliant diamond that’s not treated, and not a
diamond simulant.
• Must be at least 0.25 ct. in size, and all stones within a set should
be within 0.10 ct. of each other.
• Must be colorless to light yellow, with no brownish or grayish colors.
• No fluorescence in color masters E through J; weak fluorescence
acceptable in K through Z masters.
• Clarity grade must be no lower than SI2, with no inclusions eye-
visible through the pavilion or that affect transparency or color.
• Crown and pavilion must not be noticeably shallow or deep.
• Girdle thickness must be thin to thick; faceted girdle recommended.
• Girdle must not be heavily bearded or wavy, and have no large
naturals or large extra facets.

GIA MASTERSTONES

E F G H I J K L M N O Q S U W Y

D E F G H I J K L M N O-P Q-R S-T U-V W-X Y-Z

For D-to-Z color grading, the GIA Laboratory uses a complete set of masterstones for comparison.

Robert Weldon/GIA
To be selected as a masterstone, a diamond must meet specific criteria for carat weight, color, clarity, and cut.

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 DIAMOND GRADING LAB MANUAL

Partial Master Sets

It takes a great deal of time and expense to create a master set, but most in
the trade do not need a complete set. Many use partial sets, which can be
tailored to individual requirements. For example, a buyer who only deals
with diamonds in the G-H-I range might only need a master set that ranges
from F to J.
Another option is a 5-stone master set that represents every other color grade
between E and M. It’s more affordable than a full set and can still produce
accurate grading results.

5-STONE MASTER SET

E G I K M

D E F G H I J K L M

Synthetic Cubic Zirconia Master Sets

A set of synthetic cubic zirconia (CZ) comparison stones can cost much less
than a diamond masterstone set, but CZs don’t display the same brilliance
and fire as diamonds, so their colors can look very different. Also, depending
on how they are manufactured, CZ colors might fade over time. GIA does
not grade CZ master sets.

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DIAMOND GRADING LAB MANUAL

Masterstone Set-up
Proper set-up of the masters in the viewing environment plays a role in
obtaining accurate, repeatable results.

Here’s the set-up procedure:

1. Clean each master thoroughly with a gemcloth.
2. Using tweezers, place masters table-down against the back of the
grading tray, with the highest-color master on the left and the rest in
order of descending color—for example, E through N.
• It is always advisable to use rubber-tipped or plastic tweezers to
help reduce the risk of damage. This also eliminates the possi-
bility of leaving metal tweezer marks on the surface of a bruted
girdle, which can affect the diamond’s color.
• Be sure the masters are equally spaced, with enough room to
place the diamond being graded between them without touching.

E F G H I J K L M N

Kevin Schumacher/GIA
To prepare for color grading, use tweezers to place the masterstones table-down on the grading tray.

Over time, masters can become dirty or incur damage that can affect their
color appearance. It is a good idea to periodically give the masters a deep
cleaning and check them for damage. If a master is damaged, it should be
replaced or repaired and returned to the laboratory for re-grading.

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Viewing Environment
To produce consistent and repeatable color-grading results, you must have
a standardized viewing environment. The GIA DiamondDock™ provides a
viewing environment that consists of the following:

A daylight-equivalent fluorescent
light source (remove diffuser plate
for color grading)

A neutral gray background

A white, non-reflective grading tray

Subdued, low-level ambient lighting

in the surrounding area

Robert Weldon/GIA

While you can easily obtain use of a DiamondDock™ in a laboratory or office

setting, one is not always available or practical in other situations. You can
create a similar controlled lighting environment using the overhead light on
a standard gemological microscope and a matte-white, non-fluorescent
plastic grading tray or folding card. Remove the diffuser plate from the light
before color grading.

The overhead light

on a gemological
microscope—with its
diffuser plate
removed—and a
matte-white folding
card can provide
suitable color-
grading conditions.

Denise Conrad/GIA

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Viewing Geometry
Viewing geometry refers to the distances and angles between the diamond,
the light source, and the observer (grader). During D-to-Z color grading, the
standard viewing geometry described below minimizes the diamond’s visual
complexity—its brightness and scintillation—and maximizes consistency.
Whether you’re using the DiamondDock™ or a comparable lighting envi-
ronment for D-to-Z color grading, you should follow these steps.

To establish standard viewing geometry:

1. Center the tray under the light source to ensure the most even illu-
mination of the diamonds.
2. Hold the tray 8 inches (20 cm) beneath the light source. On the
DiamondDock™, place the tray on the grading shelf, which is
located at the proper distance from the light source.
3. Observe the diamond from a distance of 12 to 15 inches (30 to
38 cm).

8 in (20 cm)

12-15 in (30-38 cm)

Robert Weldon/GIA
The proper viewing geometry ensures consistent D-to-Z color grading.

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4. For round brilliant diamonds, evaluate color in the table-down posi-

tion only. Proper positioning for fancy shapes is explained on pages
252 to 253 of this manual.

Kevin Schumacher/GIA

5. Place the diamond you’re grading in the same line as the masters,
close to but not touching them—no more than 1/5 inch or 0.5 cm
apart.

Correct Incorrect

Both by Kevin Schumacher/GIA

6. Gently rock the grading tray to view the diamond through a subtle
range of motion, from near perpendicular to the girdle surface to
near perpendicular to the pavilion facets. This is necessary to avoid
distracting reflections and allow you to better observe the diamond’s
overall color.

Peter Johnston/GIA

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Color Grading Procedure

After the masters have been cleaned and properly set up in the viewing
environment, follow the process below to determine the color grade. Be sure
to use the proper viewing geometry, which is described above.
1. Use a gemcloth to thoroughly clean the diamond being graded.
2. Using tweezers, place the subject diamond table-down to the left of
the highest-graded color master—for example, to the left of the E
master.

D E F G H I

3. Move the diamond being graded along the row of masters until it
appears to have noticeably less color than the master to its left.
Begin your comparisons with the master that’s at least two grades
lower than what you think the color grade might be. With each
comparison, rock the grading tray to compare the diamonds
through a gentle range of up and down motion. This helps avoid
distracting reflections and allows for better observation of the
diamond’s overall color.

•
D E F G H I

4. Move the diamond being graded back to the left, placing it to the
right of each master in order, until the diamond appears to have less
color than one master but more color than the master to its left. This
narrows the grade range and identifies the closest master. As you do
this, always place the diamond close to, but not touching, the
master—they should be about 1/5 inch (0.5 cm) apart.

• •
D E F G H I

Example:
A diamond appears to have less color than the G master but more color than
the F master. There are two possibilities: The color grade might be F or G.
In this case, the unknown diamond is closest in color to the G master.

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5. To determine the final color grade, compare the diamond being

graded by moving it to the right and left sides of the closest color
master. This technique is called “wrapping the master.” This is the
point where you should be aware of the master-eye effect, which is
described on the next page.

•
D E F G H I

•
D E F G H I

6. Assign a single letter grade for D through N. Beyond that level,

assign a two-grade range in the following increments:
• O to P
• Q to R
• S to T
• U to V
• W to X
• Y to Z
If the diamond’s bodycolor is other than yellow, you might have to
use a descriptive term in combination with, or in place of, the letter
grade. These terms are described in the next section.
7. Examine the diamond being graded with a loupe or a microscope to
be sure it was not switched with a masterstone.
If the diamond was switched, use the diamond’s inscriptions or
other grading characteristics to separate the masters from the
diamond you are grading. You will need to re-grade that diamond’s
color once all of the masters are verified and placed back in the
proper order.

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Master-eye Effect
When you’re moving the subject diamond from side-to-side around the
closest master during the final color-grading stage—described previously—
it’s a good time to consider a phenomenon called the “master-eye effect.”
This occurs when the diamond and the masterstone are very close in color.
The side the diamond is on can affect its apparent depth of color, so as you
move it from left to right, its depth of color will appear to reverse.
Your final color grade depends on the “movement” of the unknown diamond’s
Jian Xin Liao/GIA depth of color. If the unknown stone appears to have the same or slightly more
This image will help you understand the color on the left but less color on the right, it’s a higher color grade than the
master-eye effect. The third and fourth
color chips from the left are exactly the
masterstone. If the unknown stone appears to have the same or more color on
same color. To most observers, the chip the left and the same or slightly less color on the right, it’s the same grade as
on the right appears to have less color. the masterstone. (Be aware that, for some people, the master-eye effect works
in the opposite direction.)
The table below describes possible appearance scenarios and their corre-
sponding grading decisions.

COMMON DIAMOND VS. MASTER APPEARANCE R ELATIONSHIPS

Appearance of diamond as compared to closest master
Grading Decision
LEFT side of master RIGHT side of master

Assign one grade higher than

master
Same or slightly more color Noticeably less or less color
than master than master Example:
• Closest master is G
• Color grade is F

Assign same grade as master

Same, slightly more, or Same or slightly less color than
noticeably more color than master Example:
master • Closest master is G
• Color grade is G

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Because of this phenomenon, it’s important to carefully compare the

diamond being graded on both sides of the master closest to it in color before
determining the final grade.

G G

Both by Kevin Schumacher/GIA

The diamond being graded is very close in color to the G master. It appears to have
less color than the G master when placed on the right but more color when placed on
the left.

Using a Partial Master Set

If you’re using a partial master set consisting of every other color grade, you
will need to estimate color grades between masters.

E G I K M

D E F G H I J K L M

Example:
A diamond has less color than the I master (after comparing it on both sides)
but more color than the G master. This means the color grade is G or H.
Assign a G if the color appears closer to the G master or an H if the color
appears closer to the I master.

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Grading Colors Other than Yellow

Diamonds with slight tints of colors other than yellow have their own unique
descriptions but are still compared to yellow D-to-Z masters.

Brown Diamonds
When comparing a brown diamond to a yellow master set, you assess the
overall depth of color (the combined effect of tone and saturation) and
compare it to the depth of color of the yellow masters.
While there is a noticeable difference in hue, the tone and saturation of brown
diamonds in the colorless to near-colorless range of the D-to-Z scale are
similar to the tone and saturation of yellow diamonds in that range. However,
To compare a brown diamond to a yellow as these stones become darker, the differences in hue, tone, and saturation
masterstone, you assess both diamonds’ become more pronounced. Therefore, the following word descriptions are
overall depth of color. used along with the letter grade for brown diamonds graded K through Z:
• K through M: Faint Brown
• N through Q-R: Very Light Brown
• S through Y-Z: Light Brown

Example:
You would describe a brown diamond with a grade of K as “K, Faint Brown.”

Gray Diamonds
The grading approach for gray diamonds is similar to—but not the same
as—that used for browns. In the colorless to near-colorless range (E to J),
they are graded using the letter grades of the D-to-Z scale. Beginning at K,
gray diamonds receive word descriptions consisting of only the terms “Faint
Gray,” “Very Light Gray,” or “Light Gray.” The grade ranges are the same
as for brown diamonds.
Although only word terms are used to describe gray diamonds in the K-to-
Z range, they are not considered “fancy” colors until they reach a description
of “Fancy Light” (the same as with yellows and browns).

Other Colors
The occurrence of subtle colors other than yellow, brown, or gray is so rare
that the presence of even slight tints is acknowledged in color grading. When
the color grade is G or lower in the table-down position, the diamond is
considered a colored diamond and you would use colored diamond color-
G master
grading procedures to determine the grade.
Kevin Schumacher/GIA
Diamonds in colors other than yellow,
brown, and gray, and with more color than
the G master, are graded using colored
diamond color-grading procedures.

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 DIAMOND GRADING LAB MANUAL

Color Grade Terminology Boundaries

This table shows the terminology associated with the D-to-Z scale, as well as the
boundaries where colors transition off the scale.

< means less than > means greater than

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DIAMOND GRADING LAB MANUAL

Special Case Guidelines

There are some special circumstances that might arise during diamond color
grading. You must be aware of them and know how to compensate for them.

Significant Size Differences

When the diamond being graded is very different in size from the master,
Robert Weldon/GIA
try to observe the overall color blend of both rather than focusing on select
In this image, a 10-plus ct. diamond is
positioned next to a 0.70-ct. J master. To
visual details. Try gazing simultaneously at the master and the diamond
make their subtle color differences stand being graded. This will make the blend of color in each diamond easier to
out, observe the overall color of the two identify regardless of their sizes.
diamonds together, rather than switching
between them.
Heavily Included Diamonds
When large, extensive, and/or colored inclusions affect or obscure the
bodycolor under normal color-grading conditions, you should allow the
effect of the inclusions to blend with the overall appearance and influence
the color grade.
If inclusions are restricted to a small area, rotate the diamond so you can’t
see the inclusions, or so they’re less visible.

Jian Xin Liao/GIA

This diamond has dense areas of dark
inclusions that give it an overall gray
appearance. You would account for this
appearance in the color grade.

Both by Jian Xin Liao/GIA

The inclusions in this diamond are limited to a small area (left). Rotate the diamond so
the inclusions are less visible (right).

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Estimating Color Grades

Comparing a diamond against a set of masterstones is the best way to determine
its color grade, but you can estimate the color grade if masterstones aren’t
available. The estimation technique isn’t appropriate for every situation, but it
can be helpful for sorting purposes and in certain buying environments.
Use the same viewing environment and distances as for color grading with
masters.

Follow this procedure to estimate a diamond’s color grade:

1. Use a gemcloth to thoroughly clean the diamond being graded.
2. Using tweezers, place the diamond table-down in a white, non-
reflective grading tray and observe the amount of color you see
through the pavilion. Decide if it appears colorless, has a slight tint
of color, or has obvious color.
Gently rock the grading tray to view the diamond through a subtle
range of motion, from nearly perpendicular to the girdle to nearly
perpendicular to the pavilion facets.
3. Place the diamond face-up in the grading tray and make the same
judgments of the diamond’s color—colorless, slight tint of color, or
obvious color.
Be aware that a diamond’s brightness and fire can affect its color in
this view. Rock and tilt the tray to better observe the overall body-
color.

1 2 3

All by Denise Conrad/GIA

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DIAMOND GRADING LAB MANUAL

4. Estimate the color grade range based on a combination of the

impressions in both positions, as outlined in the chart below:

E STIMATED COLOR G RADES

Table-Down Face-Up Color Grade Range

COLORLESS
D, E, F
Colorless
Colorless

NEAR COLORLESS
G, H, I, J
Slight tint of color
Colorless

FAINT
K, L, M
Obvious color
Slight tint of color

VERY LIGHT to LIGHT

N, O-P, Q-R, S-T,
U-V, W-X, Y-Z
Obvious color
Obvious color

Peter Johnston/GIA

5. Narrow the grade range based on the amount of color.

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FLUORESCENCE
Fluorescence is the emission of visible light by a material when it is
stimulated by ultraviolet (UV) rays. Part of diamond grading involves
describing the intensity, or strength, of a diamond’s reaction to longwave
ultraviolet light—an essential component of daylight. About one-third of
gem-quality diamonds emit some degree of fluorescence. If present, an indi-
vidual diamond’s fluorescence can be used to help identify it.
Fluorescence can vary in both intensity and color. The terms used for
describing the intensity of fluorescence are None, Faint, Medium, Strong,
and Very Strong. Most diamonds that fluoresce do so in varying strengths
of blue, but other colors, such as yellow or white, are possible.

Shane McClure/GIA
About one-third of gem-quality diamonds emit some degree of fluorescence.

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DIAMOND GRADING LAB MANUAL

Determining Fluorescence
The standard viewing environment for determining fluorescence consists of
a longwave UV lamp (366 nm) and a darkened viewing environment. A
viewing cabinet is ideal for blocking out ambient light.
It is important to protect your skin and eyes from ultraviolet rays. Never
look into an illuminated lamp. If you are not using a viewing cabinet with
a UV filter, be sure to use protective eyewear.
Before you evaluate fluorescence, grade the diamond’s color. Although rare,
some diamonds will change color temporarily when exposed to UV radiation.
Robert Weldon/GIA
A viewing cabinet blocks out ambient Follow this procedure to evaluate fluorescence:
light and provides UV light for deter-
mining fluorescence. 1. Turn on the longwave ultraviolet lamp.
Some units have both a longwave and a shortwave lamp, so be sure
that only the longwave lamp is turned on.
2. Place the diamond table-down about 2 inches (5 cm) under the light
source. Placing a diamond too close to or too far from the lamp can
cause a diamond to fluoresce more or less strongly.

1 2

Denise Conrad/GIA Robert Weldon/GIA

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 DIAMOND GRADING LAB MANUAL

3. Assign and record an intensity-range term from None to Very Strong.

Any intensity above

“strong”

None Faint Medium Strong Very Strong

• The above images are approximate representations to help you

estimate fluorescence intensity. However, they are not absolutely
accurate and are meant to be used only as guides.
• Each image approximates the greatest intensity for the specified
range. For example, if the diamond is more intense than the
“Faint” reference image, the intensity would be “Medium.”
• “None” represents a range from no fluorescence to insignificant
fluorescence.
• If the fluorescence appears uneven, assign an intensity range
that is representative of the overall appearance rather than of the
most intense point.
4. Observe and record the color of the fluorescence. Possible colors
include blue, yellow, white, orange, green, and red. On a GIA
Report, fluorescence color is listed only when the intensity is
Medium or stronger.

NOTE:
Don’t confuse fluorescence with
the reflection of the UV lamp,
shown here.

All by Robert Weldon/GIA

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DIAMOND GRADING LAB MANUAL

COLORED DIAMOND COLOR GRADING

Colored diamonds, referred to in the trade as fancy-colored diamonds,
include yellow, brown, and gray diamonds with darker tone and/or more
saturation than those that fall in the D-to-Z range, as well as diamonds with
face-up color other than yellow, brown, and gray.
The GIA Colored Diamond Color Grading System provides an effective
means of communicating color that is useful to dealer and consumer alike.
The grading system used by GIA provides terminology to describe the char-
acteristic color of the diamond being graded.

Color Descriptions and Grades

The GIA Colored Diamond Color Grading System includes a description of
the diamond’s hue and a fancy-color grade that describes the combined effect
of tone and saturation.

Fancy Color Grades (Tone and Saturation)

A description of the combined effect of tone and saturation—called the
“Fancy Color Grade”—uses one of the following terms:
• Faint
• Very Light
• Light
• Fancy Light
• Fancy
• Fancy Intense
• Fancy Dark
• Fancy Deep
• Fancy Vivid

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 DIAMOND GRADING LAB MANUAL

GIA Colored Diamond Scale

LIGHTER TONE

HUE
HIGHER
SATURATION

Fain
t cy
Fan id
y Ligh
t cy viv
r
Ve t Fan nse
ligh ht inte
c y lig
Fan
cy
y Fanep
Fan
c de

rk
LOWER c y da
Fan
SATURATION HUE

DARKER TONE

This illustration shows the interrelationship of GIA fancy color grades.

This illustration of the colored diamond scale shows the fancy color-grade
terms and how they relate to each other in the grading system. The first three
grades—Faint, Very Light, and Light—apply only to diamond colors other
than yellow. The rest apply to yellow as well as any of diamond’s many other
fancy colors.
The same fancy color grade categories are not the same size for all hues due
to differences in natural occurrence or relative rarity among various diamond
colors. Therefore, rarer colors that occur in narrow saturation ranges might
receive the same fancy-color grade at lower saturation levels than a more
commonly occurring diamond color that occurs in a wider saturation range.
The charts on pages 210 to 212 show the tone and saturation ranges for
yellow, pink, and blue diamonds.

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DIAMOND GRADING LAB MANUAL

Color Descriptions (Hue)

There are 27 basic hue terms used to describe a diamond’s color. Each term
represents a specific range of color within the hue circle, shown below.

RED
ORANGY
PURPLISH RED
RED
PURPLE- REDDISH
RED ORANGE
RED-
PURPLE ORANGE

REDDISH YELLOWISH
PURPLE ORANGE

YELLOW-
ORANGE
PURPLE
ORANGE-
YELLOW

ORANGY
YELLOW
VIOLET

YELLOW

BLUISH VIOLET

VIOLETISH GREENISH
BLUE YELLOW

GREEN-
YELLOW
BLUE
YELLOW-
GREEN

GREENISH YELLOWISH
BLUE GREEN

GREEN- GREEN
BLUE
BLUE- BLUISH
GREEN GREEN

When a description consists of more than one color, the predominant color
is stated last. Therefore, terms such as “yellow-green” and “green-yellow”
represent different hues.

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 DIAMOND GRADING LAB MANUAL

Other terms are occasionally used to better describe a hue of a particular

tone or saturation. For example:
• “Pink” replaces “red” when reddish orange to reddish purple hues
are pale.
• When applicable, “brown/brownish” and “gray/grayish” can
describe diamonds of low saturation and/or dark tone. “Warm”
colors appear brownish and “cool” colors appear grayish.

Orangy pink Blue-green Bluish-green

Pink Green-blue
Green
Grayish bluish green
Brownish pink Greenish Grayish
Purplish blue Grayish
greenish blue
pink green

Gray-green
Blue
DE Brown-pink Grayish Gray-blue
CR
EA blue
SIN
GS
AT DECR
URA
TIO EASI
NG S
N CONSTANT “LIGHT” ATUR CONSTANT “MIDDLE”
ATIO
N TONE RANGE
TONE RANGE

These two hue grids illustrate how decreasing saturation affects pink (left) and blue to green-blue (right) hue terms.
With a decrease in saturation, pink diamonds become brownish while blue to blue-green diamonds become grayish.

Black and White Diamonds

To avoid redundancy in terms (such as “dark black” or “light white”), the
term “Fancy” is the only one used in descriptions of natural-color black and
opalescent white diamonds. The full description would be Fancy White or
Fancy Black.

Fancy Black Fancy White

Robert Weldon/GIA Elizabeth Schrader/GIA

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DIAMOND GRADING LAB MANUAL

Color Distribution
Distribution is the evenness or unevenness of color you see face-up using
standard viewing procedures. In addition to the color description and fancy
grade, a description of the color distribution—stated as “uneven” or
“even”—is used for diamonds graded Fancy, Fancy Dark, Fancy Deep,
Fancy Intense, and Fancy Vivid.

Uneven Even Colored Diamond Grading Process

The grading process used for colored diamonds is different from the one
Nicholas Del Re/GIA used for diamonds in the D-to-Z range.
The color distribution of these diamonds
would be described as uneven (left) and
even (right). Viewing Environment
A standardized viewing environment is essential for producing consistent
and repeatable color grading results. The colored diamond color-grading
environment has the same requirements as the standard D-to-Z viewing envi-
ronment, including:
• A daylight-equivalent fluorescent light source
• A neutral gray background
• A white, non-reflective grading tray
• Subdued, low-level ambient lighting in the surrounding area

Eric Welch/GIA
The GIA DiamondDock™ and the The Judge II® by Macbeth provide ideal viewing
environments for evaluating colored diamonds.

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Viewing Geometry
As you learned earlier, viewing geometry refers to the distances and angles
between the diamond, the light source, and the observer (grader). The
standard viewing geometry described below is used during colored diamond
color grading to maximize consistency and minimize the visual complexity—
the effect of brilliance and scintillation—of the diamond.
The following standard viewing geometry is used for colored diamond color
grading:
• Center the grading tray directly under the light source to ensure the
most even illumination of the diamond.
• Hold the tray approximately 18 inches (46 cm) below the light
source.
• Grade colored diamonds in the face-up position.
• Observe the diamond at a distance of 12 to 18 inches (30 to 46 cm)
and at an angle of about 45° away from the light.
• Rock the tray gently to view the diamond through a subtle range of
motion, from perpendicular to the table to perpendicular to the
crown facets. Once the characteristic color of the diamond is deter-
mined, hold it in a stable position, approximately perpendicular to
the table.

Overhead light

45°

Nicholas Del Re/GIA Peter Johnston/GIA

You grade colored diamonds in the face-up position (left) and at a 45-degree angle from the light
source (right).

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DIAMOND GRADING LAB MANUAL

Characteristic Color
Diamond interacts with light in many ways. However, it is only the
characteristic color that is described in the colored diamond color-grading
system. The characteristic color is the overall impression of color you see
when you view the diamond face-up, and does not include:
• Obvious surface reflections
• Fire (color flashes)
• Windowing (washed-out, see-through areas)
• Extinction (dark, blackish areas)

Shane McClure/GIA Shane McClure/GIA Nicholas DelRe/GIA Shane McClure/GIA

The gray areas in the illustrations correspond to the areas in the diamonds above
them that display the characteristic color.

Windowing

Both by Nicholas Del Re/GIA

These photographs show a diamond in two different viewing positions. Windowing
revealed in one position (left) makes it difficult to determine the characteristic color.
The color displays best when you look directly perpendicular to the table (right).

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 DIAMOND GRADING LAB MANUAL

Color Comparison Methodology in the Lab

Once the characteristic color is determined, the grader can begin to narrow
the grade down through a process called “bracketing.” This process involves
side-by-side comparison of the diamond being graded to standard references
known as color comparators. Comparators are necessary because a person’s
visual color memory can’t reliably provide the degree of repeatability needed
to consistently identify a specific color.

Eric Welch/GIA
A GIA Laboratory grader compares the diamond to a standard reference of known
color, then compares it to several other references until the color grade is determined.

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DIAMOND GRADING LAB MANUAL

GIA Yellow Diamond Color Range

These two charts illustrate color appearances at two locations in the yellow hue
range: “cooler” colors in yellow/greenish yellow hues and “warmer” ones in
yellow/orangy yellow hues.

Fancy Fancy Fancy

Light Intense Vivid

Fancy
Fancy
Deep
Fancy
Dark

Fancy Fancy Fancy

Light Intense Vivid

Fancy

Fancy
Deep
Fancy
Dark

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 DIAMOND GRADING LAB MANUAL

GIA Pink Diamond Color Range

This chart shows tone and saturation ranges for fancy pink
diamonds, from Very Light to Fancy Red.

Faint Light
Very
Light
Fancy Fancy
Light Intense

Fancy
Vivid
Fancy

Fancy
Dark
Fancy
Deep
Fancy
Red

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DIAMOND GRADING LAB MANUAL

GIA Blue Diamond Color Range

This chart shows the blue diamond range, from Light to Fancy Vivid.

Faint

Very Light
Light

Fancy Light

Fancy

Fancy Intense

Fancy Vivid

Fancy Dark Fancy Deep

212
DIAMOND GRADING LAB MANUAL DIAMOND GRADING LAB MANUAL

GIA Colored Diamond Grading Report™

The GIA Colored Diamond Grading Report™ provides a complete quality analysis of the diamond along with
a detailed description of its color and whether the color is natural or treated.

213
G RADING FANCY CUTS 215
Parts of Fancy Shapes 217
Shape and Cutting Style 218
Shape Terms 218
Modified Shapes 219
Square vs. Rectangular Shapes 220
Novelty Shapes 220
Terms for Cutting Styles 221
Brilliant 221
Step Cut 223
Mixed Cut 223
Portrait Cut 223
Rose Cut 224
Double Rose Cut 224
Special Case Guidelines 225
Old European Brilliant and Circular Brilliant 225
Old Mine Brilliant 226
Emerald and Square Emerald Cuts 226
Baguette and Tapered Baguette 227
Briolettes and Faceted Beads 227
Branded Cuts and Trade Terms 228
Measuring Fancy Cuts 230
Determining Length and Width 230
Triangular Shapes 231
Briolettes and Faceted Beads 231
Evaluating Cut 232
Total Depth Percentage 232
Table Percentage 233
Culet Size 236
Girdle Thickness and Condition 236
Crown Angle 238
Pavilion Depth 239
Pavilion Bulge 240
Shape Appeal 241
Length-to-Width Ratio 242
Bow-tie 243
Culet Placement 244
Finish 245
Round-shape Symmetry 245

GRADING FANCY CUTS

Fancy-shape Symmetry 246
Evaluating Clarity 251
Evaluating Color 252
D-to-Z, Fancy-shaped Diamonds 252
Table-down Position 252
Face-up Position 253
G RADING FANCY CUTS
The fancy-cut category includes diamonds in shapes or cutting styles that
differ from the 57- or 58-facet standard round brilliant.
• A round shape might be cut in a non-brilliant cutting style or in a
brilliant cutting style that varies from the standard round brilliant.
For example, it might have a different number of bezels or pavilion
mains.
• Fancy cuts that are not round, such as squares or ovals, are referred
to more specifically as fancy shapes.
Evaluations of fancy-cut color, clarity, and finish are essentially based on
the same criteria and methods used for round brilliants, with some minor
differences and additional considerations to account for variations in shape
and facet arrangement.
When evaluating a fancy-cut diamond’s face-up appearance, proportions,
and design, its overall look is more important than the specific proportion
details that would be vital if it were a round brilliant. Often, what makes a
fancy cut attractive is a matter of personal taste.

Denise Conrad/GIA
You apply many of the same basic grading criteria to both round brilliants and fancy
cuts, but there are some differences between them, and some additional considera-
tions for fancy-cut diamonds.

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Diamond Grading Worksheet for Fancy Shapes

This worksheet is designed for your use in the classroom to document the grading features of fancy-
shaped diamonds. To maximize your learning experience, you will record more of the diamond’s details
than would normally be recorded by the trade or listed on a grading report.

DIAMOND GRADING WORKSHEET — FANCY SHAPE

Name: ______________________________________________________

R1-801
Stone No.: ___________________________________________________

CARAT WEIGHT: _______________

0.33 ct.

Measurements: 5.40
_______________ 3.91
x ______________ 2.47
x ______________ mm
length width depth

1.38 :________
L-to-W Ratio: ________ 1

Oval Brilliant
Shape & Cutting Style: __________________________________________

GIA 1234567891
Inscription: ___________________________________________________

CUT:

PROPORTIONS and DESIGN

63.2
Key to Symbols:
Total Depth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . _________%

2.00 mm, _________%

Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . _________ 51
Xtl
________________________
SML
Culet Size . . . . . . . . . . . . . . . . _________________________________
Ndl
________________________
ETN to _________
Girdle . . . . . . . . . . . . . . . . _________ MED , ______________
Faceted
min. max. condition N
________________________
acceptable
Crown Angle . . . . . . . . . . . . . . . . . . _________________________________ ________________________

slightly deep
Pavilion Depth . . . . . . . . . . . . . . . . . _________________________________ ________________________

n/a ________________________
Pavilion Bulge . . . . . . . . . . . . . . . . . _________________________________
________________________
BW
Shape Appeal . . . . . . . . . . . . . . . . . _________________________________
________________________
slight
Bowtie Effect . . . . . . . . . . . . . . . . . . _________________________________
________________________
n/a
Culet Placement . . . . . . . . . . . . . . . _________________________________
________________________
FINISH
________________________
TP
Polish: . . . . . . . . . . . . . ________________________________ VG
__________
features rating ________________________

UO, T/oc
Symmetry: . . . . . . . . . ________________________________ G
__________ ________________________

Comments:
features rating

CLARITY: . . . . . . . . . . . . ________________________________
minor inclusions VS 2
__________
descriptor grade _________________________________
Clouds are not shown.

COLOR: . . . . . . . . . . . . . ________________________________
_________________________________
colorless F
__________
descriptor grade _________________________________
strong
Fluorescence: . . . . . . . . . ________________________________ blue
__________ _________________________________
intensity color

_________________________________
p/n ###### © 2014 GIA _________________________________

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PARTS OF FANCY SHAPES

In addition to the terms used to describe round brilliants, the following terms
are used to describe the parts and facets of fancy shapes.

Head Cleft
Shoulder Lobe

Belly
Belly Belly

Wing
Wing Wing

Point Point Point

Head Corner
Corner
Shoulder

Belly Side Side

Bezel facet Pavilion main facet

Step facet Chevron facet

Star facet Half-moon facet

Bezel tip French tip

Bezel tip and French tip: Shapes like the marquise, pear, Keel line: The bottom of a fancy-shaped brilliant, where the
and heart are often cut with French tips. This faceting variation pavilion facets meet (shown in red). The keel line usually runs
on the bezel tip increases durability by replacing the large bezel the length of the stone and includes or passes through the
facet at the point with star and upper half facets. culet.

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SHAPE AND CUTTING STYLE

Shape and cutting style refer to a diamond’s face-up outline (shape) and
facet arrangement (cutting style). A standard naming convention is used to
describe a diamond’s shape and cutting style by using consistent, basic, and
objective terms that are easily understood by the trade as well as by
consumers.
This naming convention includes a description of the diamond’s shape,
followed by a description of its cutting style (for example, “Oval Brilliant”).

Robert Weldon/GIA
This diamond’s shape and cutting style Shape Terms
would be described as “Oval Brilliant.” These are the basic terms used to describe a diamond’s shape:

Round Cushion Oval Heart Marquise Pear

Triangular Shield Rectangular Square Rhomboid Half-moon

Lozenge Kite Trapezoid Pentagonal Hexagonal Octagonal

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Modified Shapes
A diamond’s outline can feature modifications that do not significantly alter
the basic shape, such as beveled or rounded corners, additional sides, or
arched sides. In these cases, the term “cut-cornered,” “round-cornered,” or
“modified” is added before the basic shape description.
• If the diamond has beveled or rounded corners, the basic shape
description would include the term “cut-cornered” or “round-
cornered” (for example: “Cut-Cornered Square”).
• If there are variations other than, or in addition to, beveled or
rounded corners, the basic shape description would include the
term “modified” (for example, “Modified Pear”).

Examples:

Cut-Cornered Round-Cornered Cut-Cornered Square Round-Cornered Square

Rectangular Rectangular

Cut-Cornered Triangular Round-Cornered Modified Triangular Modified Triangular

Triangular

Modified Oval Modified Pear Modified Heart Modified Shield

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Square vs. Rectangular Shapes

Strictly defined, a square has four equal sides and a corresponding length-
to-width ratio of 1:1. The distinction between square- and rectangular-shaped
diamonds is less stringent because most appear square, even with a length-
to-width ratio of up to 1.05:1.00.
The criteria listed in the table below will help you make consistent
distinctions between square and rectangular shapes.

SQUARE VS. R ECTANGULAR

t
L-to-W Ratio Shape

≤1.05:1 Square

≥1.06:1 Rectangular

≤ means less than or equal to ≥ means greater than or equal to

Example:
A diamond has a length of 5.35 mm and a width of 5.10 mm.
L-to-W Ratio = 5.35 ÷ 5.10 = 1.0490196, rounded to 1.05
= 1.05:1
Shape = Square

Novelty Shapes
A diamond might be fashioned to resemble a unique object or symbol, such
as a fish or a star. In those cases, you would use the specific shape description.
Other shapes would be simply referred to as “novelty” shapes.

Boat and racket by Tino Hammid/GIA

Diamonds can be cut in a variety of unusual shapes, as shown by these fish, horse head, sailboat, racket, and star cuts.
When the shapes are recognizable, their names are used as diamond shape descriptions.

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Terms for Cutting Styles

A diamond’s cutting style is described as brilliant, step cut, mixed cut,
portrait cut, rose cut, or double rose cut. Brilliant, step, and mixed cutting
styles are the most common. Any of these cutting styles can be applied to a
variety of different shapes.

Brilliant
A standard brilliant cut consists primarily of kite- and triangular-shaped
facets. It also has a girdle plane, a table facet, and possibly a culet. The term
“modified” is used to describe a brilliant cutting style that deviates symmet-
rically from a standard brilliant.
Round Modified Brilliants: By definition, a “Round Brilliant” consists of
57 or 58 facets. The term “Round Modified Brilliant” is used to describe a
round shape with a brilliant cutting style that deviates symmetrically from
the standard 57- or 58-facet arrangement.

Examples:

Round Modified Brilliant Round Modified Brilliant

Round Modified Brilliant Round Modified Brilliant

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Fancy-shaped Brilliants: A standard fancy-shaped brilliant has a girdle

plane, a table facet, bezel facets, star facets, pavilion mains, upper and
lower half facets, and possibly a culet.
The number of bezel, pavilion main, and half facets can differ, and the
diamond can still be described as a standard brilliant. For example, it might
have 10 bezels and 14 pavilion mains.
The term “modified brilliant” is used to describe a brilliant cutting style
with facets that are symmetrically added, deleted, or modified in a way
that differs from the standard brilliant facet arrangement.

Examples:

Pear Brilliant Oval Brilliant Cushion Brilliant

Pear Modified Brilliant Oval Modified Brilliant Cushion Modified Brilliant

Cut-Cornered Rectangular Modified Brilliant Square Modified Brilliant Cut-Cornered Triangular Modified Brilliant

NOTE:
If both the shape and the cutting style are modified, the Modified description is only used once. For example a
modified pear shape with a modified brilliant cutting style would be described as a “Modified Pear Brilliant.”

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Step Cut
A step cut consists of long, narrow, four-sided facets arranged in rows that
run parallel to the girdle. Many step cuts have three rows of step facets, but
there can be any number of rows.

Octagonal Step Cut Modified Triangular Step Cut

Mixed Cut
A mixed cut has either a brilliant-cut crown and step-cut pavilion or a step-
cut crown and brilliant-cut pavilion.

Round Mixed Cut Cut-Cornered Rectangular Mixed Cut

Portrait Cut
A portrait-cut diamond has a flat crown and a flat pavilion. The pavilion is
cut like the crown, with a large table facet that creates the appearance of a
picture frame.

Rectangular Portrait Cut Oval Portrait Cut

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Rose Cut
A rose-cut diamond has a girdle plane, a flat pavilion, and a pointed or dome-
shaped crown. The pavilion might have small facets around the outer edge.

Round Rose Cut Oval Rose Cut

Double Rose Cut

A double rose cut resembles two rose cuts placed base to base. It has a girdle
plane and pointed or dome-shaped crown and pavilion. Its facet arrangement
and proportions are similar on both sides.

Heart Double Rose Cut Pear Double Rose Cut

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Special Case Guidelines

Some cuts are similar to basic cuts, but have differing proportion sets. The
following terms are used in place of the basic shape and cutting style descrip-
tions in order to differentiate them.

Old European Brilliant and Circular Brilliant

The descriptive terms Old European Brilliant and Circular Brilliant are used
for antique-style cuts with the same shape and 58-facet arrangement as the
modern round brilliant, but with variations in their proportion sets that give
them a distinctive appearance. Circular Brilliants represent cutting innovations
that took place as the trade moved from the old European cut to the modern
round brilliant. They are sometimes referred to in the trade as “transitional cuts.”
These antique-style cuts were never meant to be judged using modern
criteria. Therefore, cut grades are not applied to them.

58-FACET ROUND B RILLIANT DESIGNATIONS

For consistency, use the specific proportion criteria listed here to classify 57- to 58-facet round
brilliant cuts.

Description Old European Brilliant Circular Brilliant Round Brilliant

Sample
Diagram

Must meet 3 out of 4: Must meet all 3: All other proportion sets
• Table: ≤53% • Star length: ≤50%
Criteria • Crown angle: ≥40° • L.h. length: ≤60%
• L.h. length: ≤60% • Culet: MED or larger
• Culet: SLG or larger

≤ means less than or equal to ≥ means greater than or equal to

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Old Mine Brilliant

An Old Mine Brilliant is an antique-style variation on a modern 58-facet
Cushion Brilliant. The same proportion criteria listed for Old European Bril-
liants in the chart on page 225 apply to Old Mine Brilliants. All other
proportion sets for this facet arrangement would be described as Cushion
Brilliants.

Old Mine Brilliant Cushion Brilliant

Emerald and Square Emerald Cuts

An Emerald Cut is a cut-cornered rectangular step cut with narrow to
moderately sized corners. The Square Emerald Cut description is used when
the outline is square.
• These shapes typically have 3 rows of step cuts on the crown and
pavilion but might have more.
• Use the criteria listed on page 220 to distinguish an Emerald Cut
from a Square Emerald Cut.
• When the corners are wide, the cut is described as a Cut-Cornered
Rectangular or Square Step Cut to distinguish it from the antique
Asscher Cut (see page 228).

Emerald Cut Square Emerald Cut

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Baguette and Tapered Baguette

A Baguette is a small, rectangular step cut. When the sides are tapered to
form an elongated trapezoid shape, the cut is described as a Tapered
Baguette.

Baguette Tapered Baguette

Briolettes and Faceted Beads

Briolettes and faceted beads have circular cross-sections and do not have
girdle planes. Facets placed around their circumferences might be triangular,
kite-shaped, or step-like. Faceted beads are spherical in shape, while briolettes
are elongated and often teardrop-shaped. A disk-shaped bead with faceted
edges is referred to as a rondelle.

Briolette Briolette Faceted Bead Rondelle

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Branded Cuts and Trade Terms

Over the years, various terms have been used in the trade to describe fancy cuts.
These are most often brand names or proprietary terms. Cutting technologies
have evolved, allowing diamond professionals to develop unique cuts that offer
important branding opportunities. Some branded cuts became common after
their patents expired and their names are now used more broadly.
Listed below are some common trade terms used to describe fancy cuts.
Radiant Cut: Cut-cornered square or rectangular modified brilliant, originally
patented in 1977. Today, this term is broadly used to describe many
variations of cut-cornered square and rectangular modified brilliants.

Asscher Cut: Cut-cornered square or sometimes rectangular step cut,

patented in the early 1900s. It’s the predecessor of the modern emerald cut,
with wide corners that are nearly octagonal in shape, a small table, a high
crown, and a deep pavilion.

Princess Cut: A square or rectangular modified brilliant. The corners might

have bezel or French tips, and the number of facets can vary.

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Quadrillion Cut: Square modified brilliant developed in 1979. It’s a pred-

ecessor of—and commonly referred to today as—the princess cut. These
continue to be marketed under the trademarked Quadrillion name and have
a narrower range of proportion sets than most princess cuts.

Trillion and Trilliant Cuts: These terms were originally trademarked

descriptions for triangular and modified triangular brilliant cuts. Today,
they’re used to describe many variations of triangular brilliants.

Trapeze Cut: This trade term is used to describe trapezoid-shaped diamonds

in various cutting styles.

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MEASURING FANCY CUTS

Measurements of round-shaped diamonds are recorded in a series, the same
as for the standard round brilliant: minimum diameter – maximum diameter
× depth (read as minimum diameter to maximum diameter by depth). Fancy-
shape measurements are recorded as “length × width × depth.”

Round Shape Measurements

Minimum Diameter – Maximum Diameter × Depth

Example:
6.50 – 6.55 × 3.92 mm

Fancy Shape Measurements

Length × Width × Depth

Example:
6.52 × 4.12 × 3.37 mm

Determining Length and Width

Typically, length is the longest dimension, measured from end to end, and width
is the widest measurement at a right angle (90°) to the length. On some shapes,
such as triangular and heart shapes, the width is longer than the length.

Width Width Width

Length Length Length

Width Width
Width

Length Length Length

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Triangular Shapes
Most triangular shapes have one side that is longer or shorter than the other
two—this side is considered the width. Length is the dimension that’s
perpendicular to the width.

To measure a triangular shape:

1. Measure all three corner-to-corner sides and select the measure-
ment that’s least like the other two. This is the width.
2. Measure the length perpendicular to the determined width.

3 Width

Length
1 2

Briolettes and Faceted Beads

The measurements of briolettes and faceted beads differ from most cuts
because they do not have defined crowns, girdles, and pavilions.

To measure a briolette and faceted bead:

1. Measure across the diameter in at least eight positions around the
circumference to determine length (largest measurement) and width
(smallest measurement).
2. Measure the depth perpendicular to the circumference, or point-to-
point on a briolette.

Length and width

Length and width

Depth
Depth

Example:
A briolette has eight diameter measurements of 3.43, 3.47, 3.45, 3.44, 3.48,
3.42, 3.43, and 3.46 mm and a depth measurement of 7.22 mm.
Measurements: 3.48 × 3.42 × 7.22 mm
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EVALUATING CUT
When you evaluate a fancy cut, look for a pleasing face-up appearance,
balanced contrast of light and dark areas, and symmetrical shape. As with
rounds, you don’t want hidden weight that is not necessary for the diamond’s
design, or thinner girdles that affect durability.

Total Depth Percentage

On round shapes, total depth percentage is calculated in the same way as
for round brilliants. For fancy shapes, you use width instead of average girdle
diameter to calculate total depth percentage.
While total depth that falls outside the normal range of 59 to 63 percent
might indicate lower cut quality for a round brilliant diamond, this is not
always the case with other shapes. For example, many princess cuts are most
attractive when they have total depths of more than 70 percent.
Total depth percentage is not applicable for briolettes and faceted beads.

To calculate total depth percentage:

1. Divide the depth in millimeters by the average girdle diameter
(round shapes) or width (fancy shapes) and multiply by 100.
2. Round the result to the nearest tenth of a percent (0.1%).

depth (mm)
Total Depth % = x 100
average girdle diameter (mm) or width (mm)

Round to nearest 0.1%

Example:
A square-shaped diamond has a width of 3.68 mm and a depth of 2.56 mm
Total depth % = (2.56 ÷ 3.68) x 100 = 69.56521
= 69.6%

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Table Percentage
For round shapes, table percentage is calculated in the same way as for the
round brilliant. For fancy shapes, the width is used in place of average girdle
diameter to calculate table percentage. Large tables up to 70 or 80 percent
are common for many step cuts and for square or rectangular diamonds.
Table percentage does not apply to rose cuts, double rose cuts, portrait cuts,
briolettes, or faceted beads.

Denise Conrad/GIA
You use a table gauge to measure a fancy cut’s table.

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To determine the table size:

1. Use a table gauge to measure the table facet.
2. Depending on the shape and facet arrangement, take one or more
measurements to determine the average, smallest, or largest table
size measurement:
• For rounds, use the same process as for round brilliants.
Measure all corner-to-corner table dimensions and then calcu-
late the average. For example, you would take five
measurements on a stone with 10 bezels.
• For square and octagonal shapes, measure the table across the
length and the width of the stone. For octagonal shapes, take
additional measurements along the diagonal. Use the smaller of
these measurements as the table size.
• On all other shapes, use the maximum table size measurement
across the width. For rectangular step cuts, measure the table
across the center. On brilliant cuts, it might be necessary to take
two measurements to determine the maximum table size.

Average table measurement Smallest table measurement

For rounds, use the average table size measurement to calculate table percentage
(left). For squares and octagons, use the smallest table measurement, determined by
measuring across the length and width, adding diagonal measurements for octagons
(right).

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Largest table measurement

For all other fancy shapes, use the largest table size measurement, as determined
across the width.

To calculate table percentage:

1. Divide table size in millimeters by average girdle diameter (round
shapes) or width (fancy shapes) and multiply by 100.
2. Round the result to the nearest whole percent (1%).

table size (mm)

Table % = x 100
average girdle diameter (mm) or width (mm)

Round to nearest 1%

Example:
A cushion-shaped diamond has a table-size measurement of 3.48 mm and
a width of 6.22 mm.
Table % = (3.48 ÷ 6.22) x 100 = 55.9485531
= 56%

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Culet Size
Culet size is evaluated for rounds using the same method as for the round
brilliant. For fancy shapes, however, culet size represents the width of the
culet relative to the width of the diamond.
As with the round brilliant, a larger culet can have a negative effect on the
diamond’s face-up appearance. However, larger culets are part of the appeal
of antique cuts like the old European.
Culet size is not a consideration for rose cuts, double rose cuts, portrait cuts,
briolettes, or faceted beads.
Culet size is the width of the culet
relative to the width of the diamond.
Girdle Thickness and Condition
Girdle thickness and condition are assessed the same as they are on round
brilliants. However, there are some additional considerations for fancy
shapes:
• Only consider the valley areas on brilliant cuts with scalloped
girdles. Consider the thickness of the entire girdle when the girdle
is not scalloped.

Mitchell Moore/GIA Gary Roskin

• Ignore girdle thickness in the cleft area on heart shapes. This area is
made thicker in order to create the shape.

Mitchell Moore/GIA

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• Carefully check the points and corners of fancy shapes. A natural,

extra facet, or facet variation at the point can create a knife-edge. If
this is the case, call the girdle extremely thin.

Knife-edge, extremely thin

• On shapes with straight sides, like the emerald cut, the girdle facet
might be tilted at an angle toward the crown or pavilion. If it is
tilted at more than a slight angle, creating a knife-edge, call the
thickness extremely thin. Treat the intended girdle facet as an extra
facet or facet variation.

Girdle facet tilted

toward pavilion, creating
a knife-edge, extremely
thin

Intended girdle facet is

considered an extra facet

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Crown Angle
On standard brilliant cuts, a crown angle that is too shallow or too steep can
affect the stone’s face-up appearance. On fancy shapes, only the angles of
the center bezel facets are considered. This is because crown angle varies
with changes in the outline. For example, you might see steep angles at a
head position and shallow angles at points.
Crown angle evaluation does not apply when judging cutting styles other
than standard brilliants.

To evaluate the crown angle:

1. Hold the diamond in profile view, table-to-culet under magnifica-
tion, using darkfield illumination.
2. Rotate the diamond to examine the crown angle:
• For round modified brilliants—for example, those with 10
bezels—rotate the diamond to examine each crown angle.
• For fancy-shape brilliants, position the diamond lengthwise and
observe the angles at the center two or four bezels across the
width.

3. Describe the average crown angle as acceptable, slightly shallow,

very shallow, slightly steep, or very steep.

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Pavilion Depth
As with the round brilliant, a pavilion that is too shallow or too deep can
affect the stone’s face-up appearance. The acceptable range for pavilion
depth varies with the shape and cutting style.
Pavilion depth evaluation applies only when judging standard brilliant cutting
styles.

To evaluate pavilion depth:

1. Examine the diamond face-up, without magnification, under
normal lighting conditions to see if it is reasonably bright.
• If it appears dark, the pavilion is probably deep.
• If it appears glassy or watery, or if the girdle’s reflection is
visible at the sides of the table, the pavilion is probably shallow.
2. Hold the diamond table-to-culet in the profile view and visually
compare the crown height to the pavilion depth.
• For most fancy cuts, the pavilion should be 2.5 to 4.5 times the
depth of its crown.
• Keep in mind that some pavilion depths are acceptable for
certain shapes that wouldn’t be acceptable for others.

1 1

2.5 4.5

3. Describe pavilion depth as acceptable, slightly shallow, very

shallow, slightly deep, or very deep.

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Pavilion Bulge
A step cut’s pavilion should slope gently from the girdle to the culet. When
the first step is cut at a steep angle, it can create a pronounced bulge. When
a stone has more pavilion bulge than is necessary for its shape, this adds
unnecessary weight to the diamond and might make the stone look dark.

To evaluate pavilion bulge of a step-cut diamond:

1. Hold the diamond table-to-culet in profile view under darkfield illu-
mination and 10X magnification.
2. Examine the stone’s profile across its length and width. There
should be an even, gentle arc from girdle to culet.
3. If there is more bulge than necessary, describe pavilion bulge as
slight, noticeable, or obvious.

A step cut’s pavilion should

slope gently from girdle to culet.
Excessive bulge, shown by the
gray areas outside the outline,
adds weight without enhancing
the diamond’s appearance.

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Shape Appeal
Even a perfectly symmetrical fancy-shaped diamond might not have a
graceful and pleasing shape. To judge shape appeal, you need to consider a
diamond’s face-up outline in relation to others of the same shape and cutting
style. It shouldn’t differ too much from the typical proportions for its shape
and style, although some proprietary cuts do deviate intentionally.
These are some shape-appeal variations that are considered by most in the
trade to have a negative effect:
• Narrow corners on shapes with beveled corners (NC)
• Wide corners on shapes with beveled corners (WC)
• High shoulders on pears or ovals (HS)
• Flat wings on marquises, pears, or hearts (FW)
• Bulged wings on marquises, pears, or hearts (BW)
• Undefined points on marquises, pears, or hearts (UP)
• Misshapen lobes on hearts (ML)
Examples:

Attractive, appealing outlines

Less appealing outlines

Narrow corners High shoulders Bulged wings Misshapen lobes

Wide corners Undefined point Flat wings Undefined point

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Length-to-width Ratio
Another aspect of shape appeal is length-to-width ratio. Many in the trade
prefer some ratios over others, while others believe that a ratio alone isn’t
enough to convey a diamond’s beauty.
5.03 mm
To calculate length-to-width ratio:
1. Divide the length in millimeters by the width and round to the
nearest hundredths (0.01). This value represents the length (L).
2. Assign a value of 1 for the width (W).
9.42 mm 3. List the ratio as L:W (for example, 1.50:1).

length (mm)
L-to-W ratio =
width (mm)

Round to nearest 0.01

Example:
A marquise has a length of 9.42 mm and a width of 5.03 mm.
L-to-W Ratio = 9.42 ÷ 5.03 = 1.87276342, rounded to 1.87
= 1.87:1

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Bow-tie
Many marquise, pear, and oval brilliants show dark areas in their patterns
that resemble bow-ties and run across the width of the stone in the center of
the table. This is especially common in shallow or very deep stones.
A bow-tie gets darker as the difference between a diamond’s length and
width increases and pavilion angle variations become more extreme. A bow-
tie can vary from light grey to black. The darker or larger it is, the more it
detracts from the face-up appearance.

To assess a bow-tie:
1. Examine the diamond face-up, without magnification, under
normal lighting conditions.
2. Describe the effect as slight, noticeable, or obvious, based on the
size and darkness of the bow-tie.

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Culet Placement
A culet that is off-center will affect the diamond’s symmetry rating.
However, there are cases when a culet is located along a shape’s line of
symmetry, but it is placed too high or too low so it detracts from the stone’s
appearance. This can occur on pear- and heart-shaped diamonds, where
symmetry is evaluated along one line of symmetry.

To evaluate culet placement:

1. Hold the diamond girdle-to-girdle in the face-up view, under dark-
field illumination and 10X magnification.
2. If the culet is not centrally located, describe the culet placement as
too high or too low.

Too high Properly placed Too low

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Finish
Polish and symmetry are evaluated on a scale from excellent to poor, using
the same criteria and grading methods as for round brilliants. There are some
differences in assessing symmetry variations, however, depending on the
diamond’s shape. Some novelty-shaped diamonds are intentionally asym-
metrical. In these cases, symmetry evaluation would not apply.

Round-shape Symmetry
Round-shaped diamonds are evaluated according to rotational symmetry.
That is, each section of the round diamond should match through a 360-
degree rotation. While the round brilliant has eight sections, the number of
sections on other round cuts can vary.

10 Sections 16 Sections 3 Sections

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Fancy-shape Symmetry
Fancy-shaped diamonds are evaluated based on line or point symmetry.
Line Symmetry: Most diamond shapes have at least one line of symmetry
that runs vertically along the length, creating two equal parts. Symmetry
evaluation is based on how closely the two parts mirror each other. On rare
occasions, a shape—such as the half-moon—might have a line of symmetry
that runs in another direction.

One line of symmetry creates two equal parts.

Many diamond shapes have two lines of symmetry: One that runs vertically
along the length and another across the width, creating four equal parts. In
this case, symmetry evaluation is based on how closely the two parts across
each line of symmetry mirror each other (side-to-side and top-to-bottom).

Two lines of symmetry create four equal parts.

Point Symmetry: Some shapes do not have

line symmetry. However, their shapes look
the same when they are rotated 180 degrees.
This is referred to as point symmetry.
Shapes with point symmetry have two
equal parts. Symmetry evaluation is based
on how closely the two parts match each
other.

Point symmetry has two equal parts.

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Fancy-shape Symmetry Variations: A fancy-shaped diamond’s outline, as

well as the number, size, shape, and placement of its facets, should match
across each line of symmetry. The following illustrations show examples of
the variations that apply to fancy shapes.

Uneven outline (UO):

The diamond’s outline should be symmetrical across each line of symmetry. An

uneven outline can include uneven shoulders, uneven lobes, uneven wings, and
uneven corners.

Table off-center (T/oc):

The table should be symmetri-
cally placed across each line
of symmetry. If the table is off-
center, the crown facets on
one side will appear larger than
the facets on the opposite side.
Looking through the table, you
will see more of the pavilion to
one side of a line of symmetry;
this might be less apparent if
the culet is offset in the same
direction.

Culet off-center (C/oc):

The culet should be symmetri-

cally placed across each line of
symmetry. On brilliant cuts with
a keel line, the line will appear
to bend when the culet is dis -
placed to either side. Looking
through the table, you will see
more of the pavilion to one side
of a line of symmetry; this might
be less apparent if the table is
offset in the same direction.

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Table/culet alignment (T/C):

You will see the same visual

indications as with table and
culet off-center. When the
table and culet are displaced in
opposite directions, the view of
the pavilion through the table
will be more exaggerated.

Misalignment (Aln):
Crown and pavilion facets
should be symmetrically
aligned across each line of
symmetry. Because the number
and type of facets can differ
from crown to pavilion, it is not
always possible for like facets
to meet at the girdle.

Misshapen facets (Fac, MB, MM, MS):

Symmetrically located facets
MB, MS across the diamond’s line of
symmetry should be the same
size and shape. On brilliant
cuts, misshapen facets are
referred to more specifically as
Fac misshapen bezel (MB),
misshapen star (MS), or
misshapen main (MM).
MM

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Non-pointing (Ptg, OB, OM, SB, SM):

Adjoining facets should meet
SM at precise points and, on bril-
liant cuts, bezel and main
facets should meet at their
OB prescribed locations. Those
that do not are referred to
more specifically as short bezel
Ptg (SB), open bezel (OB), short
main (SM), or open main (OM).

If the sides of a prospective

main or bezel are tapered, then
the facet should point properly.
If the sides of the facet are
parallel, the facet is not
intended to be a main or bezel.
This is considered a facet vari-
ation and only affects symmetry
if the facets are misshapen
(different sizes or shapes).

Open mains Facet variation

Missing facets (MF):

An asymmetrically deleted
bezel, main, lower half, upper
half, chevron, or step facet is
considered to be missing.

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Extra facet (EF):

A diamond might have facets in

addition to the standard facet
types. When placed without
regard for symmetry they are
considered extra facets and
affect symmetry. They are also
considered blemishes.

Extra facets

Additional facets that are

placed symmetrically across
each line of symmetry are
referred to as facet variations.
A facet variation affects
symmetry only if the facets are
misshapen (different sizes or
shapes).

Facet variation

Natural (N):

Naturals affect symmetry in

the same way as extra facets.
Naturals located along the
girdle edge can cause an
uneven outline.

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EVALUATING CLARITY
The same criteria and grading methods used for round brilliants apply when
evaluating the clarity of fancy cuts. However, there are some additional
considerations to keep in mind:
• You apply the same basic grading methodology for fancy cuts as
for round brilliants, dividing the diamond into smaller sections that
can be easily examined. The size of the section depends on the
shape and cutting style of the diamond.
• Inclusions might be easier to see in step cuts, but harder to see at
the points of fancy-shaped brilliants like marquises and pears, espe-
cially if they have French tips.
• Plot fancy cuts on a diagram that matches or most closely resem-
bles the shape and facet arrangement of the diamond.
• Orient the diamond to the diagram according to its length and
width. When the diagram is positioned with crown on the left and
pavilion on the right, the width runs horizontally and the length
runs vertically.

Width Length
Width
Length

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EVALUATING COLOR
Fancy-cut color is graded using the same standard viewing environment and
grading procedures as for the standard round brilliant. For fancy-shaped
diamonds in the D-to-Z color range, different viewing positions are used to
account for the effect of the diamond’s shape and cutting style on its color
appearance.

D-to-Z Fancy-shaped Diamonds

You observe fancy-shaped diamonds in a table-down position, or in a combi-
nation of table-down and face-up positions, depending on the amount of
color present.

Table-down Position
First, examine all fancy-shaped diamonds in the table-down position as you
would for rounds.
• Examine the diamond at a 45-degree angle to your line of sight.

Side view Top view

• Otherwise, assign a grade that averages the diamond’s appearance

in both the table-down and face-up positions.

Side view Top view

NOTE:
Fancy shapes can display up to three distinct color intensities, depending on their orientation
in the table-down position. The color might appear more intense when viewed lengthwise or
“washed-out” when viewed across its width. The 45-degree angle provides the best visual
“average” for observing the amount of color.

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 DIAMOND GRADING LAB MANUAL

Face-up Position
Fancy shapes toward the lower end of the D-to-Z scale often appear to have
more face-up color than round brilliant diamonds. Therefore, fancy shapes
with a color grade of Q or lower seen in the table-down position are also
viewed in the face-up position.
• If the diamond appears to have more face-up color than the Z
master, it is graded on the colored diamond color-grading scale.
• Otherwise, assign a grade that averages the diamond’s appearance
in both the table-down and face-up positions.

Eric Welch/GIA
When a fancy-shaped diamond appears to have a color grade
of Q or lower in the table-down position, compare it side-by-
side and face-up with masters before determining the final
color grade.

NOTE:
The GIA Laboratory uses a set of fancy-shaped diamonds
to represent the fancy-shape face-up boundaries for Light
yellow grade ranges (S-T, U-V, W-X, and Y-Z). These
Jian Xin Liao/GIA
diamonds supplement the round-brilliant masters, help
These masters represent (left to right) S, U, W, and Y
Kevin Schumacher/GIA
expedite the grading process, and enhance consistency. grades, and the boundary between Z and Fancy Light yellow.

253
G RADING MOUNTED DIAMONDS 255
Grading Limitations 255
Measuring Mounted Diamonds 256
Evaluating Cut 258
Table Size, Crown Angle, and Crown Height Percentage 258
Culet Size, Star Length Percentage, and Lower Half Length Percentage 259
Pavilion Depth Percentage, Pavilion Angle, and Pavilion Bulge 259
Girdle Thickness, Girdle Condition, and Painting/Digging Out 259
Girdle Thickness Percentage 260
Total Depth Percentage 262
Polish and Symmetry 263
Round Brilliant Cut Grade 263
Estimating Carat Weight 264
Estimating Weights of Small Rounds 269
Templates and Hole Gauges 274
Templates 274
Hole Gauges 275
Estimating Clarity 276
Estimating Color 278

GRADING MOUNTED
DIAMONDS
G RADING MOUNTED DIAMONDS
The same criteria for grading loose diamonds also apply to mounted
diamonds. However, you will need to use some different observation
methods to accommodate the limitations imposed by a mounting. You’ll also
often have to estimate your results rather than rely on exact measurements.

GRADING LIMITATIONS
For the following reasons, the results of mounted diamond grading are never
as accurate as the results of grading a loose diamond:
• Weight and proportions must be estimated.
• The mounting can limit your ability to see clarity characteristics
and signs of treatment.
• The mounting makes it impossible to follow the same systematic
loose-diamond grading methodology and ensure that all character-
istics are located and properly identified.
• The mounting can mask or obscure the diamond’s color.
On appraisals and other business documents, it is important to note that grading
is affected by the limits imposed by the mounting.
It is important to be aware that most laboratories do not grade mounted
diamonds. For stones previously graded by GIA, the Laboratory offers a veri-
fication service to determine whether or not the diamond matches its report.
Grading mounted diamonds and making accurate estimations takes practice.
If you have access to mounted diamonds accompanied by lab reports issued
before the stones were mounted, a good way to improve your skills is to
compare your results to those listed on the report.

A good way to improve

your skills is to compare
your practice results to
those listed on a grading
report.

Denise Conrad/GIA

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DIAMOND GRADING LAB MANUAL

MEASURING MOUNTED DIAMONDS

You measure and record a mounted diamond’s basic dimensions the same
as you would for loose stones, using tools that accommodate the mounting,
such as a millimeter gauge. For small diamonds, or when the mounting keeps
you from obtaining measurements, other tools and methods might be
necessary or helpful.
To measure a mounted diamond, use a millimeter gauge to measure the
diamond’s diameter or length and width, and depth. You can use a table
gauge to measure the basic dimensions of a small diamond.

Both by Peter Johnston/GIA

To measure a diamond in an open-back mounting (left), make sure the millimeter
gauge’s outer jaws are in contact with the top and bottom of the stone. With a
prong-set stone, measure diameter between the prongs (right).

TABLE GAUGE

Eric Welch/GIA
You can use a table gauge to measure the dimensions of small
diamonds.

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 DIAMOND GRADING LAB MANUAL

When the mounting covers the edge of the diamond, such as on bezel-set
and channel-set diamonds, you’ll have to estimate the location of the girdle’s
edge.
• On brilliant cuts, follow the bezel facet junctions to the location
where they should come to a point under the metal.
• For round shapes, measure across all four pairs of bezels, record the
minimum and maximum, then calculate the average diameter.

Both by Peter Johnston/GIA

With a bezel-set stone, estimate where the bezel facets come to a point at the girdle and measure across
the stone at those points (left). The dotted line shows the approximate position of the diamond’s girdle under
the mounting (right).

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DIAMOND GRADING LAB MANUAL

EVALUATING CUT
You use the same methods to evaluate the proportions and finish of mounted
diamonds as you use for loose stones. However, there are some minor differ-
ences and additional considerations.

Table Size, Crown Angle, and Crown Height

Percentage
You use the same method for determining table size as you would for a loose
stone, either by direct measurement or visual estimation. Direct measurement
with a table gauge is the most accurate method and can be done with most
mountings.

Eric Welch/GIA
Direct measurement of the table with a table gauge will give you the most accurate
results.

You estimate crown angle using the profile method or face-up method,
depending on the shape of the diamond and the style of the mounting.
• Use the profile method if you can see enough of the profile to make
the technique practical.
• For round brilliants, use the face-up method if the profile is
obscured by a bezel setting.
• On a round brilliant, once you have determined the table size and
Eric Welch/GIA
crown angle, use the chart on pages 124 and 125 in the cut section
Use the profile view to estimate crown
angle if the mounting allows you to see
to estimate the crown height percentage.
enough of the diamond’s profile. If it
doesn’t, switch to a face-up view.

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Culet Size, Star Length Percentage, and

Lower Half Length Percentage
Evaluate culet size, star facet length percentage, and lower half facet length
percentage in the face-up position, the same as you would for loose stones.

Pavilion Depth Percentage, Pavilion Angle, and

Pavilion Bulge
On round brilliants, you evaluate pavilion depth and pavilion angle the same
as you would for loose stones. With fancy shapes, you might be able to judge
pavilion depth and pavilion bulge if the mounting allows you to see the
stone’s profile.

Girdle Thickness, Girdle Condition, and

Painting/Digging Out
You assess minimum and maximum girdle thickness, girdle condition, and
painting/digging out the same as you would for loose stones.
If a stone is prong-set, you can judge the girdle’s visible areas. Assess the areas
hidden by the prongs by tilting the stone, looking through the table, and
observing the girdle’s reflection in the pavilion.
• The reflection of a smooth girdle looks like a uniform gray streak,
while a rough, dirty girdle has a speckled reflection.
• To see the reflection of a faceted girdle, look carefully for images
of the girdle facet junctions.

Both by Pedro Padua/GIA

To judge the girdle thickness of a prong-set diamond, examine the girdle areas that
aren’t covered (left). You can get an idea of girdle thickness in hidden areas by
observing their reflections through the table (right).

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DIAMOND GRADING LAB MANUAL

When a mounting completely conceals the girdle, you can only assess the
girdle by checking its reflection in the pavilion.
In addition to assessing minimum and maximum girdle thickness, assign an
overall description to represent the average girdle thickness. For example,
if the thickness ranges from very thin to slightly thick, the overall girdle
thickness might be medium.
You’ll need to know the diamond’s overall girdle thickness to estimate
the mounted diamond’s weight and, if needed, its girdle thickness
percentage.

Girdle Thickness Percentage

You calculate girdle thickness percentage the same as you would for loose
stones: by subtracting the crown height percentage and pavilion depth
percentage from the total depth percentage.
When it is not possible to measure the diamond’s depth or calculate its depth
percentage, you will need to refer to the chart below to estimate girdle thickness
percentage.

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 DIAMOND GRADING LAB MANUAL

E STIMATED G IRDLE THICKNESS PERCENTAGE

Select an estimated girdle thickness percentage from the typical
range shown in the row that matches the diamond’s overall girdle
thickness.
Overall Girdle Thickness Estmated Girdle
Thickness Percentage*

ETN 1.5%

VTN 2.0%

THN 2.5%

MED 3.0% to 3.5%

STK 4.0% to 4.5%

THK 5.0% to 6.0%

VTK 6.5% to 8.0%

*The estimated percentages listed here represent the

typical ranges for overall girdle thickness descriptions.
ETK 8.0% or larger Actual girdle thickness percentage is the average girdle
thickness, measured at the eight bezel-to-main “hill” posi-
tions and expressed as a percentage of average girdle
diameter.

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Total Depth Percentage

Calculate total depth percentage just like you would for loose stones: by
dividing the diamond’s depth by its average girdle diameter, or by its width
on fancy shapes.
When it is not possible to measure the diamond’s depth, such as on a closed-
back mounting, you have to estimate total depth percentage and depth in
millimeters. You will need the depth in millimeters to estimate a mounted
diamond’s weight.

To estimate depth on a round brilliant diamond:

1. Estimate the diamond’s girdle thickness percentage as described
previously.
2. Calculate the total depth percentage by adding crown height
percentage, girdle thickness percentage, and pavilion depth
percentage.
3. Calculate depth in millimeters by dividing the total depth percentage
by 100 and then multiplying the result by the average girdle diameter.
Round the result to the nearest hundreths of a millimeter.

Total Depth % = crown height % + girdle thickness % + pavilion depth %

total depth %
Depth (mm) = × average girdle diameter
100
Round to nearest 0.01 mm

Example:
A round brilliant diamond has an average girdle diameter of 8.22 mm, a crown
height of 11.5%, girdle thickness of 2.0%, and pavilion depth of 41.0%.
Total Depth % = 11.5 + 2.0 + 41.0 = 54.5%
Depth (mm) = 54.5 ÷ 100 = 0.545
= 0.545 × 8.22 = 4.4799
= 4.48 mm

11.5%

2.0%

41.0%

54.5%

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Polish and Symmetry

You evaluate polish and symmetry as you would on a loose stone, and assign
final grades based on the diamond’s appearance in a 10X loupe.
• Polish and symmetry features, such as alignment and non-pointing,
might be covered by the mounting. Reflections can help you see
areas hidden by the mounting.
• You will need to consider how the hidden features might appear at
10X with the diamond out of its mounting. For example, a notice-
ably open bezel facet that is hidden under a prong might lower a
diamond’s grade.

Round Brilliant Cut Grade

If you have Internet access, you can use the online GIA Facetware® Cut Esti-
mator to estimate the cut grade of a mounted round brilliant diamond. This
method is more accurate than using visual estimation and limiting factors
alone. If you do not have access to the Internet, visual estimation techniques
and limiting factor tables are good alternatives.

GIA Facetware® Cut Estimator

is available at www.gia.edu free
of charge in web and mobile
versions.

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ESTIMATING CARAT WEIGHT

The calculations used to estimate a mounted diamond’s carat weight are
based on formulas used by experienced professionals throughout the
diamond industry.
With practice using these weight estimation formulas, a skilled grader can
consistently estimate weight within 10 percent. Thus, a stone with an estimated
weight of 1.00 ct. might actually weigh between 0.90 ct. and 1.10 cts.
The formulas—listed on pages 266 to 267—assume symmetrically cut
diamonds with modern, standard proportions and are valid only for
diamonds, not for other gemstones.

To calculate a diamond’s estimated weight:

1. Use the weight estimation formula for the diamond’s shape, taken
from the list on pages 266 to 267.
• Each weight estimation formula has an adjustment factor that’s
based on the diamond’s shape. These are derived from experi-
ence with thousands of diamonds of known weight. For some
shapes, the adjustment factor is based on the stone’s length-to-
width ratio.
• Formulas also include a weight correction factor that’s used, if
needed, to account for thicker girdles, pavilion bulge, and shape
variations that can add to the estimated weight.
2. Determine if a weight correction is needed for girdle thickness.
• A thick girdle adds weight at the widest part of the diamond, so
girdle thickness has the greatest effect on estimated weight.
• If the overall girdle thickness is slightly thick or thicker, use the
Weight Correction Factors for Thicker Girdles chart on page 268
to determine the weight correction factor, and include it in the
estimated weight formula.
• Weight correction factors for girdle thickness apply to both
rounds and fancy shapes.

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 DIAMOND GRADING LAB MANUAL

3. On fancy shapes, determine if an additional weight correction is

needed.
• High shoulders, bulged wings, narrow corners, and pavilion
bulge can add weight to a diamond.
• If one or more of these variations is present, select a weight
correction factor between 1 and 10 percent, depending on the
severity of the variation.
• To determine the total weight correction, add this number—if
applicable—to any necessary weight correction for girdle thick-
ness. For example, if an emerald cut needs a 2 percent weight
correction for girdle thickness and a 3 percent correction for
pavilion bulge, you would need a total weight correction of
5 percent.
4. Include any necessary total weight correction in the estimated
weight formula.
• First, add the weight correction to 100.
• Divide the sum by 100 to convert the percentage to a decimal.
Use this figure in the formula.

Example:
You have determined that you need a total weight correction of 5 percent.
Weight correction factor = 100 + 5 = 105
= 105 ÷ 100 = 1.05
5. After you determine an estimated weight, take a last look at the
stone to see if your estimate is reasonable. It’s easy to make a
mistake when writing down measurements or doing calculations.
6. On appraisals or other business forms, use a qualifying statement
like “weight estimated by formula from measurements.” It’s impor-
tant for your customers or clients to understand that your estimate
is not an exact weight.

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DIAMOND WEIGHT E STIMATION FORMULAS

These formulas are most accurate when used with well-proportioned dia-
monds. If the L-to-W ratio falls between those listed, use the closest one or
choose an intermediate value.

Round Brilliant
Estimated weight = average girdle diameter2* × depth
× 0.0061 × weight correction
*This means you should take the average girdle
diameter and multiply it by itself (AGD × AGD).

Oval Brilliant
Estimated weight = average girdle diameter2* × depth
× 0.0062 × weight correction
*This means you should take the average girdle
diameter and multiply it by itself (AGD × AGD).
AGD = (L + W) ÷ 2

Heart Brilliant
Estimated weight = length × width × depth × 0.0059
× weight correction

Triangular Brilliant
Estimated weight = length × width × depth × 0.0057
× weight correction

Square or Rectangular Princess Cut

Estimated weight = length × width × depth × 0.0083
× weight correction

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 DIAMOND GRADING LAB MANUAL

Baguette
Estimated weight = length × width × depth ×
0.00915

Tapered Baguette
Estimated weight = length × average width ×
depth × 0.00915
(Width = the average of the two parallel edges)

Emerald and Radiant Cuts

Estimated weight = length × width × depth ×
adjustment factor × weight correction
L-to-W Ratio Adjustment Factor
1.00:1.00 0.0080
1.50:1.00 0.0092
2.00:1.00 0.0100
2.50:1.00 0.0106

Marquise Brilliant
Estimated weight = length × width × depth ×
adjustment factor × weight correction
L-to-W Ratio Adjustment Factor
1.50:1.00 0.00565
2.00:1.00 0.00580
2.50:1.00 0.00585
3.00:1.00 0.00595

Pear Brilliant
Estimated weight = length × width × depth ×
adjustment factor × weight correction
L-to-W Ratio Adjustment Factor
1.25:1.00 0.00615
1.50:1.00 0.00600
1.66:1.00 0.00590
2.00:1.00 0.00575

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DIAMOND GRADING LAB MANUAL

WEIGHT CORRECTION FACTORS FOR THICKER G IRDLES

These weight corrections apply to round and fancy-shape diamonds with slightly thick or thicker
girdles.

To determine the weight correction percentage:

1. In the row that matches the diamond’s overall girdle thickness, find the column containing
the closest average girdle diameter for round shapes, or width for fancy shapes.
2. Add this number to 100%, then convert the percentage to a decimal.

Example:
A round brilliant diamond has an overall girdle thickness of thick and an average girdle diameter
of 4.75 mm.
Weight correction % = 3%
Correction factor = 100 + 3 = 103% = 1.03

Overall Weight Correction %

Girdle AGD or Width (mm)
Thickness
12% 11% 10% 9% 8% 7% 6% 5% 4% 3% 2% 1%

STK ≤4.10 4.15-6.90 ≥6.95

THK ≤4.65 4.70-6.55 ≥6.60
VTK ≤4.15 4.20-4.70 4.75-5.50 5.55-6.55 6.60-8.10 ≥8.15
ETK ≤4.15 4.20-4.55 4.60-5.10 5.15-5.75 5.80-6.55 6.60-7.65 ≥7.70
≤ means less than or equal to ≥ means greater than or equal to

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 DIAMOND GRADING LAB MANUAL

Estimating Weights of Small WEIGHT E STIMATION: S MALL FULL AND

Rounds S INGLE- CUT ROUNDS
To estimate the weight of small round full-cut brilliants
or single-cut diamonds, you can refer to the chart on the
right instead of using weight estimation formulas. A
very thick girdle might require a slight upward adjustment,
but otherwise the resulting figures will be close enough.
Once you have estimated the weights of individual
diamonds, you might have to find the total estimated
weight of a cluster of small diamonds. Full Cuts Single Cuts
Here’s the procedure:
AGD Approx. Wt. AGD Approx. Wt.
1. Measure all the stones and, if possible, group (mm) (cts.) (mm) (cts.)
them into size categories.
1.3 0.010 1.0 0.005
2. Figure the total weight of each category and add 1.7 0.020 1.1 0.007
the category weights together. 1.8 0.023 1.2 0.009
1.9 0.027 1.3 0.010
Example: 2.0 0.030 1.4 0.013
A cluster-style ring has 25 full-cut rounds. Twelve 2.1 0.035 1.5 0.015
measure 2.00 mm in diameter and 13 measure 2.20 mm. 2.2 0.040 1.6 0.017
2.3 0.045 1.7 0.020
2.4 0.050 1.8 0.025
2.5 0.055 1.9 0.030
2.6 0.060 2.0 0.035
2.7 0.070
2.8 0.080
2.9 0.090
3.0 0.100
3.1 0.110
3.2 0.125
3.3 0.140
3.4 0.150
3.5 0.160
Individual weights from table:
3.6 0.170
2.0 mm / 0.03 ct. 3.7 0.180
2.2 mm / 0.04 ct. 3.8 0.200
4.1 0.250
Total weight = (12 × 0.03) + (13 × 0.04)
5.2 0.500
= 0.36 ct. + 0.52 ct. 6.5 1.000
= 0.88 ct. total weight 7.4 1.500
8.2 2.000

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DIAMOND GRADING LAB MANUAL

Sample Weight Estimation

Statistics
• Emerald-cut center stone: 7.75 mm × 4.94 mm × 3.58 mm, medium
girdle
• First emerald-cut side stone: 5.01 mm × 3.85 mm × 2.75 mm, thick
girdle
• Second emerald-cut side stone: 4.90 mm × 3.67 mm × 2.40 mm, thin
Joel Beeson/GIA girdle

Center Stone Calculations

Length-to-width ratio = (7.75 ÷ 4.94):1.00
= 1.5688:1.00, round to 1.57:1.00
Since that’s close to 1.50:1.00, you can use a 0.0092 adjustment factor. This
stone needs no girdle thickness correction factor because the girdle is
medium.
Estimated weight = 7.75 × 4.94 × 3.58 × 0.0092
= 1.2609, round to 1.26 cts.

First Side Stone Calculations

L-to-W ratio = (5.01 ÷ 3.85):1.00
= 1.3013:1.00, round to 1.30:1.00
Since this is between the ratios of 1.00:1.00 and 1.50:1.00, find those ratios
on the emerald-cut adjustment factor chart and interpolate between them. In
this case, take the adjustment factor for a 1.00:1.00 ratio and the factor for
a 1.50:1.00 ratio and average them.
(0.0080 + 0.0092) ÷ 2 = 0.0086
Since the girdle is thick and the width of the stone is 3.85 mm, the weight
correction from the chart should be 4 percent.
Estimated weight = 5.01 × 3.85 × 2.75 × 0.0086 × 1.04
= 0.4744, round to 0.47 ct.

Second Side Stone and Total Weight Calculations

L-to-W ratio = (4.90 ÷ 3.67):1.00
= 1.3351:1.00, round to 1.34:1.00
Since this is between the ratios of 1.00:1.00 and 1.50:1.00, find those ratios
on the emerald-cut adjustment factor chart and interpolate between them. In
this case, 0.0086 would work. This stone needs no girdle thickness
correction factor because the girdle is thin.
Estimated weight = 4.90 × 3.67 × 2.40 × 0.0086
= 0.3712, round to 0.37 ct.
The ring’s total estimated weight = 1.26 + 0.47 + 0.37 = 2.10 cts.

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Sample Weight Estimation

Statistics
• Oval center stone: 7.90 mm × 5.60 mm × 3.69 mm, thick girdle
• First pear-shaped side stone: 7.10 mm × 4.80 mm × 2.90 mm, thick
girdle
• Second pear-shaped side stone: 7.08 mm × 4.78 mm × 2.67 mm,
medium girdle
Joel Beeson/GIA

Center Stone Calculations

Average girdle diameter = (7.90 + 5.60) ÷ 2
= 6.75
Because the stone has a thick girdle, it will require a 3 percent correction
factor, as taken from the Weight Correction Percentage Chart.
Estimated weight = 6.752 × 3.69 × 0.0062 × 1.03
= 1.0737, round to 1.07 cts.

First Side Stone Calculations

L-to-W ratio = (7.10 ÷ 4.80):1.00
= 1.4792:1.00, round to 1.48:1.00
Since this is very close to the 1.50:1.00 ratio, you can use 0.00600 as the
adjustment factor.
Because the stone has a thick girdle, it will require a 3 percent correction
factor, as taken from the Weight Correction Percentage Chart.
Estimated weight = 7.10 × 4.80 × 2.90 × 0.00600 × 1.03
= 0.6107, round to 0.61 ct.

Second Side Stone and Total Weight Calculations

L-to-W ratio = (7.08 ÷ 4.78):1.00
= 1.4812:1.00, round to 1.48:1.00
Since this is very close to the 1.50:1.00 ratio, you can use 0.00600 as the
adjustment factor.
This stone needs no girdle thickness correction factor because the girdle is
medium.
Estimated weight = 7.08 × 4.78 × 2.67 × 0.00600
= 0.5421, round to 0.54 ct.
The ring’s total estimated weight = 1.06 + 0.61 + 0.54 = 2.21 cts.

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Sample Weight Estimation

Statistics
• Radiant-cut center stone: 7.95 mm × 6.75 mm × 4.63 mm, thin to
medium girdle
• First trilliant-cut side stone: 6.95 mm × 6.73 mm × 3.00 mm, thin to
medium girdle
• Second trilliant-cut side stone: 6.92 mm × 6.71 mm × 2.98 mm, thin
Joel Beeson/GIA to medium girdle

Center Stone Calculations

L-to-W ratio = (7.95 ÷ 6.75):1.00
= 1.1778:1.00, round to 1.18:1.00
This falls between the ratios 1.00:1.00 and 1.50:1.00, so you can interpolate
between the corresponding adjustment factors 0.0080 and 0.0092. In this
case, 0.0086 will work.
Estimated weight = 7.95 × 6.75 × 4.63 × 0.0086
= 2.1367, round to 2.14 cts.

First Side Stone Calculations

Estimated weight = 6.95 × 6.73 × 3.00 × 0.0057
= 0.7998, round to 0.80 ct.

Second Side Stone and Total Weight Calculations

Estimated weight = 6.92 × 6.71 × 2.98 × 0.0057
= 0.7887, round to 0.79 ct.
The ring’s total estimated weight = 2.14 + 0.80 + 0.79
= 3.73 cts.

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Sample Weight Estimation

Statistics
• Oval center stone: 8.68 mm × 5.78 mm × 3.74 mm, medium girdle
• First princess-cut side stone: 4.01 mm × 2.51 mm × 2.21 mm
• Second princess-cut side stone: 4.00 mm × 2.57 mm × 2.22 mm
• Round accent stones: 4.10 mm diameter and 4.15 mm diameter

Joel Beeson/GIA
Center Stone Calculations
Average girdle diameter = (8.68 + 5.78) ÷ 2
= 7.23
Estimated weight = 7.232 × 3.74 × 0.0062
= 1.2121, round to 1.21 cts.

First Side Stone Calculations

Estimated weight = 4.01 × 2.51 × 2.21 × 0.0083
= 0.1846, round to 0.18 ct.

Second Side Stone Calculations

Estimated weight = 4.00 × 2.57 × 2.22 × 0.0083
= 0.1894, round to 0.19 ct.

Accent Stone and Total Weight Calculations

The rounds are full cut, so according to the chart on page 269, they each
weigh approximately 0.25 ct.
The ring’s total estimated weight = 1.21 + 0.18 + 0.19 + 0.25 + 0.25
= 2.08 cts.

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Templates and Hole Gauges

Templates and hole gauges are other tools you can use to estimate a
diamond’s weight as well as its diameter or width. They’re especially useful
for estimating the weights of small diamonds in multi-stone settings. While
these tools allow for a quick reading of a diamond’s size, the weights
obtained this way are approximate. Weight estimation formulas, explained
above, will get you closer to the diamond’s actual weight. Also, these tools
only work for diamond weight estimation—they don’t work for colored
stones.

Templates
A template is a transparent sheet of plastic imprinted with outlines of
diamonds of various shapes and sizes, along with their corresponding
estimated weights. To use a template, align the diamond being examined
with the outline that most closely matches it and read the carat weight on
the template.

Matching a diamond to its outline on a template can provide you with an estimated weight.

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Hole Gauges
A hole gauge is a metal or plastic plate with openings that represent various
diamond dimensions. Some hole gauges also have round tabs that stone
setters use to measure the spaces in settings that require replacement stones.

Eric Welch/GIA
The openings in a hole gauge help you measure diamond dimensions.

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Estimating Clarity
A diamond’s mounting limits the viewing angles and interferes with the
lighting needed to locate and identify clarity characteristics. While the
criteria for assigning a clarity grade are the same as for loose diamonds, you
will need to use a different assessment method.

To estimate the clarity of a mounted diamond:

1. Thoroughly clean the diamond.
2. Examine the interior and surface of the diamond, looking for clarity
characteristics.
• Use different viewing angles to see as much of the stone as possible.
• To examine the area hidden by a prong, find its reflection in the
opposite side of the pavilion and carefully examine the area
around it. Rocking the stone back and forth can make a hidden
inclusion’s reflection visible.
• A fiber-optic light can be useful for illuminating the areas under
the prongs.
3. Plot clarity characteristics as you would on loose stones, with some
exceptions:
• Plot prongs and other metal using a dashed black line.
• If you can’t determine if a characteristic reaches the pavilion
surface, plot it on the crown. Make a note that states, “All char-
acteristics shown on crown diagram.”

Fiber-optic light

Both by Valerie Power/GIA

You must use a variety of viewing angles to find and identify clarity characteristics in a
mounted diamond (left). A fiber-optic light will help you illuminate the areas under the
prongs (right).

The locations of the prongs on this ring (left) are indicated by black dashed lines on
its plot (right).

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4. Assign a clarity grade based on the diamond’s appearance in a 10X

loupe. You will need to consider how hidden characteristics might
appear if the diamond was loose.
• Assign a two-grade range for diamonds under 0.20 ct.
• Assign a single grade for large diamonds.
5. Be sure to note that you graded the stone under the limitations
imposed by a mounting.

Denise Conrad/GIA
As with loose stones, the clarity grade of a mounted diamond is based on its appear-
ance in a 10X loupe.

NOTE:
On higher-clarity diamonds, you might
have to remove the diamond from the
mounting to obtain accurate grading
results. The difference between IF
and VVS can have a dramatic effect
on a diamond’s value.
Under circumstances like this, it’s a
good idea to submit the diamond to a
laboratory for grading.

Fronter Photography & Associates

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ESTIMATING COLOR
A mounting makes color grading a challenge because it interferes with a
clear pavilion view, and the color of the metal can influence the diamond’s
apparent color. The lighting and background are the same for evaluating the
color of a mounted diamond as they are for grading the color of a loose stone,
but the comparison methods are very different.

To estimate the color of a mounted diamond on the D-to-Z color scale:

1. Thoroughly clean the diamond.
2. Compare the diamond being graded to the masterstones against a
non-reflective white background. Use 10X or slightly lower magni-
fication and a daylight equivalent overhead light source. Depending
on the mounting, use one of the following comparison methods.
• Use the same set-up and basic methodology as for loose stones,
but hold the mounting so the diamond is in the table-down posi-
tion as you move it along the masters.
• With the masterstone in tweezers or an adjustable ring-shaped
clamp, hold its table very close to, but not touching, the table of
the mounted stone, and compare corresponding areas of their
crowns. Compare the diamond to one masterstone at a time and
repeat the process until you find the closest match. Be sure to
keep track of which masterstone you are using so you are sure to
assign the appropriate grade.
• If the crown is not visible in the profile view, hold the diamond
and the masterstone side-by-side to perform a face-up color
comparison.
3. Assign an estimated color grade.
• Assign a two-grade range for diamonds under 0.20 ct.
• Assign a single grade for larger diamonds.
4. Be sure to note that you graded the stone under the limitations
imposed by the mounting.

NOTE:
For diamonds mounted in yellow-gold prongs, you might want to hold the
masterstone in tweezers or a clamp with gold-toned tips.

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 DIAMOND GRADING LAB MANUAL

Both by Eric Welch/GIA

For color estimation, one method is to hold the mounting so the diamond is in the table-down
position as you move it along the row of masters.

Both by Denise Conrad/GIA

Another color-estimation process involves comparing the diamond to one masterstone at a time
under 10X magnification (left). Hold them so their tables are close but not touching (right).

Denise Conrad/GIA
If the crown is not visible in profile, you must perform a face-up comparison of the diamond and
the masterstones.

279
TREATMENTS, SYNTHETICS, AND SIMULANTS 281
Diamond Treatments 282
Fracture Filling 283
Identification 283
Visual Indications of Fracture Filling 284
Grading and Disclosure 288
Laser Drilling 289
Identification 289
Grading and Disclosure 294
Surface Coating 295
Identification 295
Grading and Disclosure 297
Artificial Irradiation 298
Identification 298
Grading and Disclosure 300
High-pressure, High-temperature (HPHT) Annealing 301
Identification 301
Grading and Disclosure 305
Annealing 306
Identification 306
Grading and Disclosure 306
Synthetic Diamonds 307
Identifying Synthetic Diamonds 307
Grading Synthetic Diamonds 311
Synthetic Diamond Clarity Grading 311
Synthetic Diamond Color Grading 313
Synthetic Diamond Disclosure 315
Treated Synthetic Diamonds 316
Diamond Simulants 317
Separating Diamonds from Diamond Simulants 317

SYNTHETICS, SIMULANTS
TREATMENTS,
TREATMENTS, SYNTHETICS, AND
SIMULANTS
In this section, you will learn about the various diamond treatments,
synthetic diamonds, and diamond simulants seen in the market today.
While some treatments and synthetics can be identified using standard
gemological equipment, others can only be detected with advanced laboratory
testing. Diamond simulants, however, are easily distinguished from diamond
using basic gemological tests and observations.
All major trade organizations, as well as regulatory agencies such as the US
Federal Trade Commission, require full disclosure of diamond treatments
and synthetic diamonds with each sale, from wholesaler to end consumer.
Therefore, it is important for you to:
• Be familiar with the possible types of treatments and synthetic
growth methods.
• Know how to recognize the signs of treatment or synthetic origin
with the use of standard gemological equipment.
• Recognize when advanced laboratory testing is needed to positively
identify a treated or synthetic diamond.
Diamond treatments and synthetics are constantly evolving, so it’s important
for you to stay up-to-date with the latest processes and detection methods.
A valuable source of information is Gems & Gemology (G&G), GIA’s
professional trade journal. All G&G articles are available free of charge at
www.gia.edu/gems-gemology.

Gems & Gemology contains valuable information about gems and their sources. It is
available on the GIA website, free of charge. To access the Gems & Gemology website
via your mobile device, scan the QR code at right.

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DIAMOND TREATMENTS
Attempts to improve a natural diamond’s appearance by masking or altering
its color or by reducing the visibility of its clarity characteristics can result
in the use of one or more treatment methods.

Fracture Filling

CLARITY

Laser Drilling
DIAMOND
TREATMENTS Surface Coating

}
Artificial Irradiation
COLOR
Might be combined
HPHT Annealing in a multi-step
process
Annealing

This chart outlines the types of clarity and color treatments used to improve diamond
appearance.

It is important to be aware that a diamond often undergoes multiple

treatments to achieve the desired result. For example, it is common to see a
diamond with both laser drill-holes and fracture filling, and HPHT annealing
can be used in combination with artificial irradiation to produce colors that
a single treatment alone cannot produce.

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Fracture Filling
Fracture filling treatment involves injecting a molten glass filler into a
diamond’s surface-reaching inclusions. The filler has a refractive index (RI)
close to diamond’s RI, so it makes inclusions or fractures less visible.

Both by Shane McClure/GIA

Before fracture filling After fracture filling

Identification
Microscopic examination is necessary for the detection of fracture filling.
• During the clarity grading process, carefully examine surface-
reaching inclusions for visual indications of the presence of a filler.
On the following pages, you’ll find descriptions and examples of
the features that indicate treatment.
• You will need to use different viewing angles, a variety of lighting
techniques, and as much magnification as needed to properly iden-
tify the treatment.

If you’re ever unsure about the presence of fracture filling in a diamond,

send it to a gemological laboratory for identification.

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Visual indications of fracture filling

Flash effect: You will often observe flash-effect colors in a filled feather.
The flash effect occurs when one color appears in darkfield and a different
color appears when you switch to brightfield illumination. The second color
is usually the complementary color to the first on a color wheel.

Tips for observing flash effect:

• Rock the diamond from darkfield to brightfield illumination.
• Look along the edge of the fracture, using a viewing direction that’s
nearly parallel to it.
Denise Conrad/GIA
You can use a fiber-optic light to make • The effect might be very noticeable or very subtle, depending on
the flash effect easier to see. Position the type of filler or its position in the diamond. A fiber-optic light
the light at an oblique angle (not vertical
or horizontal) to the fracture. will enhance the flash effect and make it easier to see.

Flash-effect examples:

Both by John Koivula/GIA

This diamond’s yellowish orange flash effect, seen in darkfield (left), changed to blue
when the stone was rotated to brightfield (right).

Both by Shane McClure/GIA

This diamond’s flash effect appears purple to violet in darkfield illumination (left) and
blue-green to yellowish green in brightfield (right).

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 DIAMOND GRADING LAB MANUAL

Both by Vincent Cracco/GIA

This diamond was laser drilled as well as fracture filled. The fracture shows a pinkish
purple flash in darkfield (left) and a yellowish green flash in brightfield (right). The flash
effect is more visible in the reflection of the feather seen in the table facet.

Both by Shane McClure/GIA

This filled diamond shows no flash effect in darkfield (left). The use of intense fiber-
optic lighting reveals a subtle blue flash (right).

The flash effect can be difficult to detect in a colored diamond if it’s masked by the
diamond’s bodycolor. You would be able to see the orangy yellow flash effect in this
diamond if its bodycolor weren’t orange (left). In brightfield, the flash effect appears
bluish green (right).

NOTE:
Do not confuse the flash effect with
the iridescence or staining sometimes
seen in untreated fractures. Unlike
the flash effect, these features do not
exhibit the same change in color and
are more readily seen looking perpen-
dicular to the fracture.
Shane McClure/GIA John Koivula/GIA

Natural iridescence in an unfilled fracture Iron oxide staining in an unfilled fracture

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DIAMOND GRADING LAB MANUAL

Gas bubbles: You might see rounded, flattened gas bubbles inside filled
fractures. Numerous small gas bubbles sometimes appear along the edge of
a feather.

Shane McClure/GIA John Koivula/GIA

The gas bubbles in this filler range from The group of smaller gas bubbles in
large to very small. this filled fracture creates a cloud-like
appearance.

Areas of reduced transparency: A wider area in a fracture might not accept

or hold the filler, so it appears white or shiny, much the same as before the
fracture was filled. This most commonly occurs in areas of the fracture that
break the surface, resulting in incomplete filling at the surface that looks
like a scratch.

Shane McClure/GIA Shane McClure/GIA

The surface of this filled fracture has These filled fractures show signs of
whitened areas of reduced transparency. incomplete filling at their surfaces.
It also displays the flash effect and gas
bubbles.

Cracked filler: Filler can develop a web-like texture or dendritic (branch-like)

pattern as it cools and shrinks. Injected filler can also display a crackled texture.

John Koivula/GIA Shane McClure/GIA

The crackled texture of the filler is This filler displays both crackled texture
obvious in this fracture. and gas bubbles.

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 DIAMOND GRADING LAB MANUAL

Cloudy filler: The filler can develop a cloudy appearance when

it’s exposed to heat or ultraviolet light.

Shane McClure/GIA
The filler in this diamond has a cloudy
appearance.

Surface residue: In rare situations, damaged filler can seep out

of the fracture. It can leave a residue that looks like a white haze
or form solidified droplets around the area where the fracture
breaks the surface.

John Koivula/GIA
Exposure to the flame of a jeweler’s torch
caused the filler material to sweat out of the
fracture.

Yellow color of the filler: Some fillers are yellow, and their color
can become visible if the filled area is relatively wide, as with a
cavity or laser drill-hole.

Shane McClure/GIA
If a filler is yellow, the yellow color can
become obvious in thicker or wider areas.

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DIAMOND GRADING LAB MANUAL

Flow structure: Under magnification, filler sometimes looks like a glassy

substance melting into a narrow, open space. This so-called flow structure
is most easily viewed with the use of the shadowing technique. This involves
lighting the stone directly from below, with the baffle closed, and partially
closing the iris diaphragm to act as a shield between the light and part of the
stone. It improves contrast and makes characteristics like flow structure look
much more three-dimensional.

John Koivula/GIA Eric Welch/GIA

This diamond has a stress fracture. Its transparent flow structure (left) is easier to
detect using the shadowing technique (right).

Grading and Disclosure

Fracture filling is a non-permanent treatment. If the filler is damaged or removed,
the diamond’s apparent clarity, and possibly its color, can change. Therefore,
most gemological laboratories, including GIA, do not grade filled diamonds.
However, the GIA Laboratory does issue identification reports for filled
diamonds that are submitted. The report clearly discloses the treatment in the
comments section.
Whether you appraise, grade, or sell a filled diamond, it is imperative that
you clearly disclose the presence of this treatment.

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Laser Drilling
Laser drilling creates an opening in the diamond to provide access for
lightening or dissolving dark inclusions with bleach in an attempt to reduce
their visibility. Laser-drilling treatment results in a laser drill-hole or internal
laser drilling channel, depending on the method used. Both of these features
are considered clarity characteristics.

Vincent Cracco/GIA Vincent Cracco/GIA

One type of laser drilling reaches an Internal laser drilling creates a surface-
internal inclusion and exits through the reaching feather or expands a pre-existing
diamond’s surface. The drill-hole that feather between a dark inclusion and the
results provides access to the internal surface. The created or expanded feather
inclusion for bleaching. provides access for bleaching.

Identification
Microscopic examination is used to detect and identify laser drilling.
• Laser drilling is identified during the clarity grading process, using
the same systematic grading methodology used to locate and iden-
tify other clarity characteristics.
• You will need to use different viewing angles, different lighting
techniques, and as much magnification as needed to properly iden-
tify the treatment.

If you’re ever unsure about the presence of laser drilling in a diamond, send
it to a gemological laboratory for identification.

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DIAMOND GRADING LAB MANUAL

Laser drill-hole appearance and considerations:

• The drill-hole typically appears as a fine hollow tube with a tiny
circular opening at the surface.
• The drill-hole extends to the internal inclusion that is being treated.
• When inclusions lie close to a facet surface, it can be difficult to
locate their associated laser drill-holes. It helps to look carefully
from an angle that allows you to see the entire area between the
inclusion and the facet surface. Increase magnification as much as
needed to properly detect the presence of the treatment.
• Laser drill-holes might be widened in an attempt to make them
resemble natural diamond features such as cavities.
• Laser drill-holes might change direction or taper inward, with the
widest point at the surface.

Laser drill-hole examples:

Shane McClure/GIA Mitchell Moore/GIA

This laser drill-hole breaks the surface at This short laser drill-hole extends to an
the table facet and tapers slightly as it internal fracture. Also visible is a mirror
extends to the inclusion. reflection of the drill-hole and fracture.

Vincent Cracco/GIA Vincent Cracco/GIA

In this diamond, multiple laser drill-holes This laser drill-hole exhibits changes in
extend to the internal fracture width and direction.
surrounding an included crystal. Minute
feathers extend from the channels
created by the laser-drilling treatment.

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 DIAMOND GRADING LAB MANUAL

LASER DRILL-HOLE VS. NATURAL ETCH CHANNEL

Be careful not to confuse laser drill-holes with natural etch channels. This
chart describes the common appearances of both to help you distinguish
them from one another.

Laser Drill-hole Appearance Etch Channel Appearance

Vincent Cracco/GIA Mitchell Moore/GIA

Typically has a rounded opening Typically has an angular opening

Shows no growth-like features Interior surface often has striations—

growth-like features—perpendicular to
their length

Extends to the internal inclusion being Does not extend to an internal

treated inclusion, but might be associated with
an internal inclusion by chance

Drag lines typically not present—might Drag lines might be present since etch
be present if repolished after treatment channels are present during polishing

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Internal laser drilling appearance and considerations:

• The drilling typically appears as irregular channels that are white,
gray, or black in darkfield and dark in brightfield illumination.
• The drilling is contained within the plane of a feather, which is
usually transparent.
• The associated feather connects the inclusion being treated to the
surface of the diamond in order to provide access for bleaching.
• The drilling area itself is sometimes very small and, at 10X, can
look like a natural inclusion.
• Higher magnification is often needed to properly identify internal
laser drilling.
• Diffused lighting can make internal laser drilling more apparent.
Both by Kevin Schumacher/GIA
To create diffused light, place a white Internal laser drilling examples:
tissue (top) or diffuser plate (bottom)
over the well light.

Vincent Cracco/GIA Shane McClure/GIA

This diamond’s internal laser drilling is This diamond’s internal laser drilling
quite obvious as very irregular chan- channel appears dark in darkfield illumi-
neling. Note that the associated feather nation. The associated feather is large,
is transparent and the drilling does not and breaks across the bezel facet. The
meet the surface. inclusion being treated is at the top right.

Shane McClure/GIA Shane McClure/GIA

Brightfield illumination reveals an internal Internal laser drilling looks dark in dark-
laser drilling feature with its mirror reflec- field. Note the irregular outline of the
tion off the table facet. The surrounding drilling and the transparency of the
feather and its mirror reflection are also surrounding feather.
visible.

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 DIAMOND GRADING LAB MANUAL

I NTERNAL LASER DRILLING VS. LASER MANUFACTURING R EMNANT

Be careful not to confuse internal laser drilling with laser manufacturing
remnants–which are NOT the result of treatment. This chart lists common
appearances of each to help you distinguish these characteristics from one
another.

Internal Laser Drilling Appearance Laser Manufacturing Remnant

Appearance

Shane McClure/GIA Vincent Cracco/GIA

Associated fracture must break the Associated fracture might or might not
surface to provide access for bleaching break the surface

Associated fracture extends to the Associated fracture does not extend to

internal inclusion being treated an internal inclusion, but it might
become associated with an internal
inclusion by chance

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DIAMOND GRADING LAB MANUAL

Grading and Disclosure

Laser drilling is a permanent process, so grading reports are issued
for laser-drilled diamonds. GIA clearly discloses the presence of
laser drilling on its reports.
On GIA grading reports with a plot, laser drill-holes are always
plotted and listed first in the key to symbols. Internal laser drilling
is listed in the report’s comments section.
On GIA grading reports without a plot, including the GIA
Diamond Dossier®, both laser drill-holes and internal laser
drilling are listed first in the characteristics list.

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Surface Coating
The application of a surface coating on a diamond can hide faint bodycolor
and make the diamond appear more colorless, or create a much stronger
color. Coatings can range from the primitive, such as ink or nail polish, to
the advanced, such as a durable thin-film calcium fluoride coating.

Identification Kevin Schumacher/GIA

Most coatings can be detected with microscopic examination.

During the clarity-grading process, carefully examine the surface of each
facet for indications that the diamond was coated. Although the appearance
will vary greatly depending on the method used, some key indications
include the following:
• Colored streaks, spots, and stains on the surface
Kevin Schumacher/GIA
• Areas without color in a colored diamond
• Faint, thin, bluish, or purplish lines or spots on a colorless or near-
colorless diamond
• Scratched or damaged coating
• Oily looking facets
• Iridescent surface film
• Unusual facet color when viewed in reflected light

On the following pages, you’ll find images of coated diamonds. You will
need to use different lighting techniques, and as much magnification as
needed, to properly identify the treatment.
• Diffused transmitted light can make coatings more visible on color-
less or near colorless diamonds.
Denise Conrad/GIA
• Some coatings are more apparent in reflected light. To create diffused light, place a white
tissue (top) or diffuser plate (middle)
If you’re ever unsure about the presence of surface coating, send it to a gemo- over the well light. Keep the baffle
logical laboratory for identification. Advanced testing methods might be closed and the well light turned up all
the way. To use reflected light, turn off
needed to positively identify the treatment. the well light and illuminate the diamond
from above using an overhead light
source (bottom). You can also tilt the
diamond in the well to reflect light off a
facet surface.

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DIAMOND GRADING LAB MANUAL

Surface coating examples:

John Koivula/GIA Shane McClure/GIA

The blue coating is obvious on this Under diffused lighting, colorless areas
diamond’s girdle. The coating masks the are visible where the coating was worn
yellow bodycolor, making the diamond away.
appear more colorless.

Vincent Cracco/GIA Wuyi Wang/GIA

Bluish spots on the bezel and upper half You can sometimes see an interference-
facets indicate the presence of a related colored film when you view
coating. coated diamonds with diffused, reflected
light. For example, this green-coated
diamond displays a purple film.

Shane McClure/GIA Wuyi Wang/GIA

This coating, which looks like an iridescent Dark stains and colorless spots and
film, is present on most of the diamond. scratches are visible in this surface
Also visible are scratches and areas where coating.
the coating was removed. Reflected light is
best for viewing clues to this type of
coating.

The coated area (left) shows a bronze-

colored appearance when viewed in
reflected light. The difference is obvious
when you compare it to the reflected-light
appearance of an uncoated facet on the
same diamond’s crown (right).
Both by Shane McClure/GIA

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Grading and Disclosure

All surface coatings are considered non-permanent. Coatings can differ in
their durability: Some inks wash off with alcohol, while other coatings are
more durable. If the coating is damaged or removed, the diamond’s color
can change. Therefore, most gemological laboratories, including GIA, do
not grade coated diamonds.
Coated diamonds submitted to the GIA Laboratory are issued an identification
report with the treatment clearly disclosed in the comments section.
Whether you appraise, grade, or sell a coated diamond, it is imperative that
you clearly disclose the presence of this treatment.

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Artificial Irradiation
There are many artificial irradiation techniques that result in green
or blue diamond color. These include exposure to electrons in a
linear accelerator, irradiation with gamma rays, and exposure to
neutrons in a nuclear reactor. Subsequent controlled heat treatment,
Both by Mike Breeding/GIA called annealing, can change the blue-to-green colors to various
Before After shades of yellow or orangy yellow. In a few rare cases, the color
artificial irradiation artificial irradiation can be changed to pink or red.

Identification
Most artificially irradiated diamonds are not identifiable by a
gemologist using standard gem-testing equipment. They must be
submitted to a laboratory for an “origin of color” determination.
Laboratory gemologists and researchers use a combination of
advanced tests including absorption spectroscopy in the UV-Vis
and infrared ranges as well as luminescent spectroscopy to detect
the treatment. However, some visual features can indicate that the
diamond was treated.
Some indications that a diamond is irradiated are explained below.

Previous GIA Report

If the stone was previously issued a GIA report, you can use
GIA Report Check to confirm the authenticity of the report and
You can verify a GIA report using the online GIA its results. Any treatments are clearly disclosed on the report.
Report Check, located at www.gia.edu
It is possible that a diamond was treated after a report was
issued. If the report does not list a color treatment, compare the
diamond’s color to the color listed on the report to determine if
it might have been altered.

Inscription
Look for an inscription that identifies the treatment or links the
diamond to a GIA report that can be verified online. A diamond
identified by GIA as artificially irradiated is inscribed with the
word “IRRADIATED,” or with its GIA report number and a
registered name that’s exclusive to the process used.
Inscriptions are sometimes bleached out (white) or partially
removed by re-polishing. Therefore, examine the girdle closely
Mitchell Moore/GIA
under high magnification to look for the remnants of an inscrip-
Artificially irradiated diamonds submitted
to GIA are inscribed to provide clear tion. Be aware that an inscription can also be completely
disclosure of the treatment. removed.

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Color and Color Zoning

• All irradiated diamonds are colored and do not fall within the D-to-
Z color scale.
• Although some irradiated diamonds look very natural, unnatural-
looking color is a good indication that the diamond might be
treated.
• Many irradiated diamonds have uneven, facet-related, or shape-
related color zoning. If you see this type of color zoning, you
should submit the diamond to a lab for further testing.
• Diamonds irradiated in a cyclotron might show an umbrella pattern
around the culet. This is caused by a reflection of darkening along
the girdle. Examine the culet area through the table facet under
magnification to look for an umbrella effect.
• Some irradiated diamonds show color zoning at the culet area. This
zoning does not follow a pattern like the umbrella effect seen in
cyclotron-treated diamonds. Holding the diamond girdle-to-girdle,
examine the culet area in profile view. Use diffused lighting to
make the zoning more apparent.
• Irradiated “black” diamonds are actually dark green, dark blue, or
sometimes orange. To identify an irradiated black diamond, use
strong transmitted light.

Both by John Koivula/GIA

The “umbrella effect” seen in these diamonds indicates that they were irradiated in a
cyclotron. The diamond on the right was subsequently heat-treated. Most irradiated
diamonds today are not irradiated in a cyclotron, so there’s no color zoning at their
culets.

John Koivula/GIA Shane McClure/GIA Shane McClure/GIA

These diamonds were irradiated in an electron accelerator. The diamond on the right Strong transmitted light shows that this
was subsequently heat-treated. Under diffused lighting, both diamonds show color “black” irradiated diamond is actually
concentrations in their culet areas. very dark blue.

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Grading and Disclosure

Artificial irradiation (with or without subsequent annealing) is
considered stable under the conditions that a diamond would
normally be subjected to. Therefore, grading reports are issued for
artificially irradiated diamonds.
The GIA Laboratory prominently discloses the treatment as
follows:
• Every artificially irradiated diamond is inscribed with the
word “IRRADIATED” or with a registered name exclu-
sive to the process, along with the GIA Report Number.
• The origin of color is listed on the report as “Artificially
Irradiated.”
• An asterisk is placed after the color grade to reference a
note in the report’s comments section.

Most green diamonds are irradiated, but the origin of the irradiation
can be natural or artificial. Even with advanced laboratory testing,
it is not always possible to conclusively establish whether a green
diamond was irradiated in the ground or in a laboratory. The
presence of natural green irradiation stains helps to identify the
origin of color as natural. When laboratory testing is inconclusive,
GIA lists the color origin as “Undetermined” on its report.

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High-pressure, High-temperature (HPHT)

Annealing
Diamonds can be treated with a combination of high pressure and high
temperature by a controlled heating process called annealing. The purpose
is to either lighten off-color stones or create colors such as pink, blue, yellow,
Both by Mike Breeding/GIA
and yellow-green. This treatment alters the color of diamond by reorganizing
Before HPHT annealing After HPHT annealing
defects in the diamond’s crystal lattice. Diamonds that have undergone
HPHT annealing are referred to as “HPHT-processed” or “HPHT-treated.”
A combination of HPHT annealing and irradiation—with or without
subsequent high-temperature annealing under low pressure—can be used to
produce an even wider range of colors such as pink or orange.

Identification
HPHT-annealed diamonds cannot be identified by a gemologist with
standard gem-testing equipment. Definitive identification requires advanced
testing in a properly equipped gemological laboratory. However, you can
use a process of elimination to identify stones that require advanced testing.
Look for the following indications that a diamond was, or might have
been, HPHT-treated.

Previous GIA report with disclosed treatment

• If the stone was previously issued a GIA report, you can use GIA
Report Check to confirm the authenticity of the report and its
results. The report clearly discloses any detected treatments.
• A diamond might have been treated after a report was issued. If the
report does not list any color treatments, compare the diamond’s
color to that listed on the report to determine if it might have been
altered.

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DIAMOND GRADING LAB MANUAL

Inscription that identifies the treatment or links the diamond to its

GIA report
• Treated diamonds are often inscribed by the treater or a laboratory to
further disclose the treatment. When HPHT treatment was first intro-
duced, the treater inscribed the diamonds “GE POL.” Today, HPHT
annealed diamonds are commonly inscribed “HPHT processed,”
“Treated Color,” or with a registered name exclusive to the treatment
such as Bellataire or Suncrest.
• “Treated color” and the registered name “Suncrest” are used to
describe diamonds that were treated with both HPHT annealing and
artificial irradiation.
• Look for an inscription that links the diamond to its GIA report,
which can be verified online.
• Inscriptions might be bleached out or partially removed. Therefore,
examine the girdle closely under increased magnification to look
for an inscription. Be aware that an inscription might have been
removed completely.

All by Mitchell Moore/GIA

The inscriptions in these images indicate that the diamonds were treated with HPHT
annealing or a combination of HPHT and irradiation.

Shane McClure/GIA
This diamond’s inscription was bleached
out, so it’s less noticeable, even under
magnification.

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 DIAMOND GRADING LAB MANUAL

Features that indicate treatment, and are visible under magnification

HPHT annealed diamonds occasionally display the following visual features
under magnification. In general, these indicators are not always present, or
they are not adequate to fully establish a correct identity. Also, untreated
diamonds can display similar features.
Graphitized feathers: This is the formation of graphite around a treated
diamond’s mineral inclusions and feathers, resulting from the extreme
conditions of HPHT treatment.

John Koivula/GIA Shane McClure/GIA

Graphite formed around these diamonds’ inclusions, in a process called graphitization.
This feature can indicate that the diamond was HPHT-treated.

“Partially healed” feathers: The extreme heat and pressure of HPHT

treatment can give feathers a network-like or fingerprint-like appearance.

Both by Shane Elen/GIA

Partially healed feathers can have a network-like (left) or fingerprint-like (right) appear-
ance. They indicate that the diamond might be HPHT treated, although untreated
diamonds can have similar-looking feathers.

Damaged facet surfaces: HPHT treatment can cause damage to a diamond’s

surface. Most HPHT-treated diamonds require re-polishing after treatment.

Both by Shane Elen/GIA

Surface damage during HPHT treatment can cause a frosted or pitted appearance (left).
Damaged facet surfaces might remain on the diamond, even after re-polishing (right).

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DIAMOND GRADING LAB MANUAL

Screening Processes for HPHT-treated Diamonds

Only certain diamond types, primarily type IIa, can be decolorized by HPHT
annealing. The vast majority of colorless to near-colorless diamonds cannot
be decolorized, so their color must be considered of natural origin.
There is commercially available equipment, such as the GIA DiamondCheck™,
the DTC DiamondSure™, or the SSEF Diamond Spotter, that can be used
to screen colorless to near-colorless diamonds to determine if they are a type
that can be HPHT-treated. If they are, the diamonds should be submitted to
a gemological laboratory for advanced testing to confirm their treatment
status.
GIA DiamondCheck™: This device can separate natural diamonds from
possible HPHT-treated diamonds (as well as synthetic diamonds and non-
diamond materials) based on features of their infrared absorption spectra.
The device refers certain stones, which then require further analysis to
determine their treatment status and identification.
DTC DiamondSure™: This instrument analyzes visible absorption spectra
to identify stones that require further testing to confirm their treatment status.
SSEF Diamond Spotter: Diamonds that can be HPHT-treated are transparent
to shortwave UV light. This means that SWUV light passes through them.
The SSEF Diamond Spotter identifies diamonds that are transparent to
SWUV light and therefore require further testing for treatment detection.

GIA DiamondCheck™ DTC DiamondSure™

Kevin Schumacher/GIA

SSEF Diamond Spotter

Maha Tannous/GIA

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 DIAMOND GRADING LAB MANUAL

Grading and Disclosure

Like irradiation, HPHT annealing is considered stable under the conditions
that a diamond would normally be subjected to. Therefore, a GIA grading
report can be issued. Because HPHT treatment can be difficult to identify,
GIA issues only a full grading report that includes a plot.
The GIA Laboratory prominently discloses the treatment as follows:
• Every diamond identified as HPHT annealed is inscribed “HPHT
PROCESSED,” “TREATED COLOR,” or with its GIA Report
Number and a registered name exclusive to the treatment such as
Bellataire or Suncrest.
• “Treated color” and “Suncrest” labels indicate diamonds that have
undergone both HPHT annealing and artificial irradiation.
• An asterisk after the color grade references a note in the comments
section.
• Colored diamond reports also list origin of color as “HPHT
Processed” or “Treated.”

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Annealing
Annealing is a treatment that uses high heat and low pressure. It is often
used after a diamond is irradiated to alter the blue-to-green color created by
that treatment. When used alone, annealing can create black diamonds by
inducing large-scale graphitization within surface-reaching fractures.

Identification
In general, treated-color black diamonds are not difficult to identify. Strong
illumination will reveal their graphite inclusions confined to fractures, in
contrast to the random “salt and pepper” appearance of natural black stones.
These stones also generally lack the pitted and knotted surface features
common in natural black diamonds, and they can display a characteristic
surface iridescence.

Elizabeth Schrader/GIA Vincent Cracco/GIA

This diamond’s black color is the result of annealing (left). An isolated feather in the
pavilion displays prominent graphite inclusions along the fracture plane (right).

Elizabeth Schrader/GIA Vincent Cracco/GIA

Under transmitted light, this natural-color black diamond (left) shows randomly
dispersed graphitization (right) in a salt-and-pepper pattern.

Grading and Disclosure

Annealing is considered stable under the conditions that a diamond would
normally be subjected to. Annealed diamonds, however, do not conform to
the Flawless-to-I3 clarity scale, so a full grading report is not issued. A
colored diamond report might be issued, however.
The GIA Laboratory prominently discloses the treatment as follows:
• Origin of color is listed on the report as “Treated.”
• An asterisk is placed after the color grade to reference a note in the
report’s comments section.

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SYNTHETIC DIAMONDS
A synthetic diamond has all the same optical and physical properties of a
natural diamond, but it was grown in a laboratory rather than by nature.
Two known processes currently used in commercial production to grow
gem-quality synthetic diamonds are:
High-pressure, High-temperature (HPHT): These synthetics are grown
under controlled high-pressure and high-temperature conditions. Carbon
atoms crystalize around a natural or synthetic diamond seed crystal. A
molten metallic flux acts a solvent for the powdered carbon and a catalyst
for growth.
Chemical Vapor Deposition (CVD): These synthetics are grown using a
microwave beam or an antenna that causes carbon to precipitate out of a plasma
cloud and deposit onto a surface made of synthetic diamond, natural diamond,
or silicon. The synthetic diamond forms as the carbon deposits build.

Identifying Synthetic Diamonds

Many synthetic diamonds cannot be identified by a gemologist using
standard gem-testing equipment. They must be submitted to a laboratory for
advanced testing and conclusive identification. You will need to follow a
process of elimination to confirm the identity of stones that require advanced
testing.
Look for the following indications that the diamond is natural, synthetic, or
requires laboratory testing:

Previous GIA Report with disclosed identification

• If a GIA report was previously issued for the stone, you can use GIA
Report Check to confirm the authenticity of the report and its results.
• Synthetic diamonds are reported on a synthetic diamond report that
clearly discloses their identification.

Inscription that identifies the diamond as synthetic or links the

diamond to its GIA report
• Synthetic diamonds are often inscribed by the producer or a labora-
tory to identify them as such.
• The inscriptions commonly consist of the following text: “Labora-
tory Grown,” “Lab Grown,” “Synthetic,” “Man-Made,” or
“[Creator]-Created” (for example “Chatham-Created”).
Mitchell Moore/GIA
• Also, look for an inscription that links the diamond to its GIA The GIA Laboratory inscribes synthetic
report, which can be verified online. diamonds with their GIA report numbers,
along with the term “Laboratory Grown”
• Inscriptions might be bleached out (white) or partially removed by to further disclose their identity.
re-polishing. Therefore, examine the girdle closely under increased
magnification to look for an inscription. Be aware that an inscrip-
tion can also be completely removed.

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DIAMOND GRADING LAB MANUAL

Clarity characteristics that indicate natural or synthetic diamond

Natural and synthetic diamonds contain different types of clarity characteristics
because of their growth conditions. These characteristics help identify them
as natural or synthetic. Examine the diamond under magnification for the
characteristics listed below.
The following characteristics, when present, indicate that the diamond is
natural:

John Koivula/GIA
Included mineral crystals: Only natural diamonds can have included mineral crystals. However, synthetics can have metallic flux
inclusions (HPHT) or dark non-diamond carbon inclusions (CVD) that are similar in appearance to the crystals, needles, pinpoints,
and clouds found in natural diamonds.

Vincent Cracco/GIA Mitchell Moore/GIA

Twinning wisps Natural etch channels Triangular growth markings

Mitchell Moore/GIA Vincent Cracco/GIA Vincent Cracco/GIA

Patches of natural green (left) or brown (right) radiation staining Transparent internal graining in a
cubic pattern

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 DIAMOND GRADING LAB MANUAL

The following characteristics, when present, indicate that the diamond is

synthetic:

James Shigley/GIA John Koivula/GIA Shane McClure/GIA

Metallic flux inclusions: Solidified metallic flux can become trapped inside HPHT-grown synthetic diamonds. Because natural
diamonds are not attracted to rare-earth magnets, you can sometimes use a magnet to test for synthetic origin. However, the size
and quantity of metallic inclusions in modern synthetics have been diminishing for some time, so they are often small and difficult
to recognize.

All by Wuyi Wang/GIA

Non-diamond carbon inclusions: Irregularly shaped, dark, non-diamond carbon inclusions are sometimes found inside CVD-
grown synthetics.

Shane McClure/GIA John Koivula/GIA John Koivula/GIA

John Koivula/GIA John Koivula/GIA John Koivula/GIA

Synthetic diamond growth patterns: HPHT-grown synthetics might display hourglass-shaped, funnel-shaped, or cross-shaped
growth patterns. Look for signs of these growth patterns in internal graining, surface graining, color zoning, or fluorescence.

NOTE:
Both natural and synthetic diamonds can have the same types of blemishes and surface-reaching inclusions,
including feathers, chips, and cavities. Therefore, the presence of these characteristics does not aid in identification.

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DIAMOND GRADING LAB MANUAL

Screening Processes for Synthetic Diamonds

Colorless to near-colorless synthetic diamonds are only found in certain
diamond types, primarily type IIa. The vast majority of colorless to near-
colorless diamonds are natural.
There is commercially available equipment, such as the GIA DiamondCheck™,
the DTC DiamondSure™, or the SSEF Diamond Spotter, that can be used
to screen colorless to near-colorless diamonds to determine if they are a
type that might be synthetic. If so, the diamond should be submitted to a
gemological laboratory for advanced testing to confirm its identity.
GIA DiamondCheck™: This device can separate natural diamonds from
possible synthetic diamonds (as well as from HPHT-treated diamonds and
non-diamond materials) based on features of their infrared absorption
spectra. The device refers certain stones, which then require further analysis
to determine their identity.
DTC DiamondSure™: This instrument analyzes visible absorption spectra
to identify stones that require further testing to confirm their identity.
SSEF Diamond Spotter: Colorless to near-colorless synthetic diamonds
are transparent to shortwave UV light, which means that SWUV light passes
through the diamond. The SSEF Diamond Spotter identifies diamonds that
are transparent to SWUV light and therefore require further testing to
confirm their identity.

GIA DiamondCheck™ DTC DiamondSure™

Kevin Schumacher/GIA

SSEF Diamond Spotter

Maha Tannous/GIA

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 DIAMOND GRADING LAB MANUAL

Grading Synthetic Diamonds

All grading procedures and methods used for natural diamonds also apply
to grading synthetic diamonds. The only differences are the fineness levels
used to report clarity and color grades, and the types of internal inclusions
that might be present in natural vs. synthetic diamonds.

Synthetic Diamond Clarity Grading

The evaluation of synthetic diamond clarity follows the same methods and
procedures as those used for natural diamonds. However, the grading terms
are broader than those used for natural diamonds.

SYNTHETIC DIAMOND CLARITY SCALE

The clarity grade ranges for synthetic diamonds are broader than those used
to evaluate natural diamonds.

Synthetic Diamond Clarity Terms Natural Diamond Clarity Terms

Flawless Flawless

Internally Flawless Internally Flawless

VVS1
Very Very Slightly Included
VVS2

VS1
Very Slightly Included
VS2

SI1
Slightly Included
SI2

I1
Included I2
I3

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DIAMOND GRADING LAB MANUAL

The types of clarity characteristics in synthetic diamonds vary from those

seen in natural diamonds because of differences in their growth conditions.
Synthetic diamonds do not contain the following inclusions:
• Included mineral crystals (crystal, cloud, needle, pinpoint)
• Twinning wisps
• Natural radiation stains (patches of color)
• Etch channels

Synthetic diamonds might contain remnants of growth that are similar in

appearance to natural crystal, needle, cloud, or pinpoint inclusions.
• The same plotting symbols for crystal, cloud, needle, and pinpoint
are used to represent remnant inclusions. The symbols used are
based on the appearance of the inclusions.
• The remnants are listed in the key to symbols as Flux Remnant
(HPHT) or Growth Remnant (CVD), depending on the synthetic
growth method.

Because of the implications of the terms natural and indented natural, the
respective terms crystal surface and indented crystal surface are used to
describe these features in synthetic diamonds.
All other clarity characteristics might be found in both natural and synthetic
diamonds. Therefore, the same plotting symbols and terms apply to both.

SYNTHETIC DIAMOND CLARITY CHARACTERISTICS

When these descriptions appear on a report, this is what they mean.
Characteristic Definition Plot and Key
Flux remnant Remnants of the growth process trapped • Plotted the same as a crystal, needle, cloud, or
Growth remnant inside the polished synthetic diamond pinpoint based on its appearance face-up at 10X
consisting of metallic flux (HPHT) or non- • Listed as flux remnant (HPHT) or growth remnant
diamond carbon inclusions (CVD) (CVD) in the key to symbols based on its growth
method

Crystal surface Part of the original skin of the synthetic • Plotted the same as a natural
diamond crystal • Listed as “crystal surface” in key to symbols

Indented crystal Part of the original skin of the synthetic • Plotted the same as an indented natural
surface diamond crystal that indents at 10X • Listed as “indented crystal surface” in key to symbols
magnification

All other inclusions See definitions in clarity section • Plotted and listed using the same symbols and terms
and blemishes as natural diamonds
(feather, chip, cavity,
polish features, etc.)

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 DIAMOND GRADING LAB MANUAL

Synthetic Diamond Color Grading

The evaluation of synthetic diamond color follows the same methods and
procedures as those used for natural diamonds. However, the grading terms
are broader than those used for natural diamonds, as described below.

D-TO -Z SYNTHETIC DIAMOND COLOR SCALE

The color-grade ranges for synthetic diamonds are broader than those used
when evaluating natural diamonds.

Synthetic Diamond Color Terms Natural Diamond Color Terms

Colorless D, E, F

Near Colorless G, H, I, J

Faint K, L, M

Very Light N, O-to-P, Q-to-R

Light S-to-T, U-to-V, W-to-X, Y-to-Z

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DIAMOND GRADING LAB MANUAL

SYNTHETIC COLORED DIAMOND COLOR SCALE

The color-grade ranges for colored synthetic diamonds are broader than those used when evaluating
colored natural diamonds.

GIA Synthetic Colored Diamond Scale Synthetic Diamond Natural Diamond

LIGHTER TONE
Color Terms Color Terms

Faint Faint

HUE Very Light Very Light

HIGHER
SATURATION
Light
Fain
t Light
Vivid Fancy Light
Verhyt Inte
nse
lig
Ligh
t Fancy Fancy
p
Fanc
y Dee
Intense Fancy Intense

LOWER Dark
Dark Fancy Dark
SATURATION HUE
Deep Fancy Deep
DARKER TONE
Illustration of GIA color grade interrelationships Vivid Fancy Vivid

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Synthetic Diamond Disclosure

In the United States, Federal Trade Commission guidelines specify that it is
unfair or deceptive to represent a synthetic diamond using the word diamond,
stone, gem, or gemstone unless these terms are immediately preceded by
one of the following terms:
• Synthetic
• Laboratory-grown or lab-grown
• Laboratory-created or lab-created
• [Manufacturer name]-created, such as Chatham-created
The GIA Laboratory prominently discloses the identity of synthetic
diamonds as follows:
• Every synthetic diamond is inscribed with its unique GIA report
number along with the term Laboratory Grown or an equivalent
FTC-approved term.
• GIA synthetic diamond reports are distinct in color and appearance
from natural diamond reports.
• An identification line item on the report lists its Laboratory Grown
origin.
• An asterisk is placed after the identification to reference a note in
the comments section.

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DIAMOND GRADING LAB MANUAL

Treated Synthetic Diamonds

Synthetic diamonds can undergo the same clarity and color treatments as
natural diamonds, so the same treatment grading and disclosure criteria
apply to both, with the exception of HPHT annealing and artificial
irradiation. Because a synthetic diamond is created in a lab, its origin of
color is not relevant.

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DIAMOND SIMULANTS
Diamond simulants are natural or manmade materials that look like diamonds
and are used in their place. Some common diamond simulants include:
Synthetic Cubic Zirconia (CZ)
Synthetic Moissanite
Glass
Zircon
Synthetic Spinel
Synthetic Rutile
Synthetic Sapphire
Strontium Titanate
Yttrium Aluminum Garnet (YAG)
Gadolinium Gallium Garnet (GGG)

Separating Diamond from Diamond Simulants

Most diamond simulants are easy to detect if you know the properties of
diamond. The chart on page 321 compares diamond properties to those of
common diamond simulants.
The following are some key properties and tests that separate diamond from
simulants:
Reaction to thermal diamond tester: Diamond has high thermal conductivity,
so you can separate most diamond simulants—an exception is synthetic
moissanite—from natural or synthetic diamond with a thermal diamond
tester, also called a diamond probe. The tester can be used on both loose and
mounted stones.

This tester identifies, detects, and separates diamond from moissanite and other
diamond simulants. Be aware that not all thermal diamond testers can identify
synthetic moissanite.

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DIAMOND GRADING LAB MANUAL

Doubling: Diamond is singly refractive. Some diamond simulants, including

synthetic moissanite, are doubly refractive, so they show doubling. Under
magnification, look through crown or pavilion facets for a doubling of the
facet junctions.

Shane Elen/GIA
Magnification will reveal the doubling of facet
junctions in synthetic moissanite.

Fracture type: In diamond, fractures are step-like, with alternating straight

cleavages. Many simulants have curved, or conchoidal, fractures.

Vincent Cracco/GIA Mike Havstad/GIA

A larger chip in a diamond often shows step-like breaks (left). Many simulants display
curved fractures (right).

High dispersion: Some simulants, like synthetic CZ, synthetic moissanite,

synthetic rutile, and strontium titanate, have significantly higher dispersion
than diamond, so they show more fire.

Pedro Padua/GIA
Diamond (left) and synthetic rutile (right) show obvious differences in their displays of
fire. This is a result of synthetic rutile’s higher dispersion rating.

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 DIAMOND GRADING LAB MANUAL

Read-through effect: Well-proportioned round-brilliant simulants with a

refractive index (RI) below strontium titanate, including zircon, GGG, and
YAG, can display a read-through effect. To check for this effect, place the
diamond or simulant table-down over lines of printed text and examine the
text through the pavilion.

Eric Welch/GIA
Some diamond simulants display a read-through effect, meaning text is visible through them when you look
through their pavilions. Note that there’s no read-through with the diamond at the far left.

Pavilion flash: CZ and YAG might show a distinct flash of color across their
pavilions. To check for pavilion flash, examine the stone pavilion-up,
looking perpendicular to the culet. Be sure to hold the stone still as you
examine it: Do not rock and tilt it. Also, pavilion flash is best seen on well-
proportioned round brilliant cuts.

John Koivula/GIA Mike Havstad/GIA

This CZ displays a distinctive orange This YAG’s pavilion flash is blue.
pavilion flash.

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DIAMOND GRADING LAB MANUAL

Polish quality: Because diamond is a lot harder than any simulant, it takes
a high-quality polish, with very sharp facet junctions. Because of their
relative softness, simulants’ facet junctions appear more rounded than a
diamond’s facets. Most simulants quickly show signs of wear, with scratches
and visible abrasions.

Both by Shane McClure/GIA

Because of their relative softness, the facet junctions of simulants (left) appear more
rounded than those on a much-harder diamond (right).

Girdle appearance: Only a diamond’s girdle can be bruted. The girdles of

some simulants can be fashioned to imitate the look of bruting, but they often
have striations.

Mitchell Moore/GIA
This CZ’s girdle displays a distinctive The bruted girdle of a diamond has a
pattern of striations. waxy, granular appearance.

320
 COMPARATIVE CHARACTERISTICS OF “COLORLESS” DIAMOND AND DIAMOND S IMULANTS
DIAMOND DISPERSION SG RI
STONE DOUBLING HARDNESS ADDITIONAL CHARACTERISTICS
TESTER (fire) (heft) (see-through effect)*

• sharp facet junctions

.044 • may contain mineral inclusions
Diamond positive no 3.52 2.417 10
(moderate) • step-like breaks
• affinity to grease
DIAMOND GRADING LAB MANUAL

• near colorless with tint of green or yellow, often modified with

possible grayish or brownish
Synthetic yes .104 3.22
positive 2.648- 2.691 9.25 • stringers, needles, often perpendicular to table
Moissanite reaction
(strong) (extreme) (lighter)
• negative crystals
• conchoidal fracture

• near colorless with a tint of yellow or blue

yes .330 4.26 • commonly very worn with abraded facet junctions
Synthetic Rutile negative 2.616- 2.903 6-6.5
(extreme) (extreme) (heavier) • generally no internal inclusions, may contain gas bubbles
• conchoidal fracture

• commonly very worn with abraded facet junctions

yes .038 4.73 • various natural inclusions
Zircon negative 1.925-1.984 6-7.5
(strong) (moderate) (heavier) • conchoidal fracture
• hazy transparency

yes .018 4.00 • gas bubbles

Synthetic Sapphire negative 1.762-1.770 9
(very weak) (weak to none) (heavier) • conchoidal fracture

• obvious polish (scratches and abrasions)

.190 5.13
Strontium Titanate negative no 2.409 5-6 • generally no internal inclusions, may contain gas bubbles
(extreme) (heavier)
• conchoidal fracture

• orange pavilion flash* over most facets

2.150
Synthetic Cubic .060 5.80 • generally no internal inclusions, may contain unmelted zirconium
negative no (slight see-through 8.5
Zirconia (CZ) (strong) (heavier)
effect)*
and gas bubble-like inclusions
• conchoidal fracture

• blue and orange pavilion flash*

1.970
Gadolinium Gallium .045 7.05 • generally no internal inclusions, may contain gas bubbles and
negative no (moderate see-through 6.5
Garnet (GGG) (moderate) (heavier)
effect)*
triangular platelet inclusions
• conchoidal fracture

1.833 • blue and violet pavilion flash* over most facets

Yttrium Aluminum .028 4.55
negative no (strong see-through 8.25 • generally no internal inclusions, may contain gas bubbles
Garnet (YAG) (weak) (heavier)
effect)* • conchoidal fracture

.020 3.64 • may contain gas bubbles

Synthetic Spinel negative no 1.728 8
(weak to none) (heavier) • conchoidal fracture

• may contain gas bubbles

• rounded facet junctions
Glass negative no variable variable variable variable
• conchoidal fracture
• possible concave facets and mold marks

• separation plane between materials

DIAMOND GRADING LAB MANUAL

Assembled stones consist of two or more pieces of material glued or fused together.

321
Assembled stone • crown and pavilion may have different RI, inclusions, dispersion
Properties and tests vary depending on the materials used.
and luster

*Best seen on well-proportioned round brilliants.