International Stan 772412

INTERNATIONAL ORGANIZATION FOR STANDARDIZATION*MEX~YHAPO~HAR OPTAHM3Al.&lR IlO CTAHC\APTbl3Al&lM.ORGANlSATlON INTERNATIONALE DE NORMALISATION

Paints and varnishes - Colorimetry -

Part 2 : Colour measurement
Peintures et vernis - Colorimhie - Partie 2 : Mesurage de la couleur

First edition - 1984-10-01

iTeh STANDARD PREVIEW
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ISO 7724-2:1984
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f1eeebaded71/iso-7724-2-1984

UDC 667.6 : 535.65 Ref. No. IS0 7724/2-1984 (E)

Descriptors : paints, varnishes, calorimetry, tests, apparatus, spectrophotometers, calorimeters.

Price based on 6 pages

Foreword
IS0 (the International Organization for Standardization) is a worldwide federation of
national standards bodies (IS0 member bodies). The work of preparing International
Standards is normally carried out through IS0 technical committees. Every member
body interested in a subject for which a technical committee has been established has
the right to be represented on that committee. International organizations, govern-
mental and non-governmental, in liaison with ISO, also take part in the work.

Draft International Standards adopted by the technical committees are circulated to

the member bodies for approval before their acceptance as International Standards by
the IS0 Council. They are approved in accordance with IS0 procedures requiring at
least 75 % approval by the member bodies voting.

iTeh STANDARD PREVIEW

International Standard IS0 7724/2 was prepared by Technical Committee ISO/TC 35,
Paints and varnishes.
(standards.iteh.ai)
ISO 7724-2:1984
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f1eeebaded71/iso-7724-2-1984

0 International Organization for Standardization, 1984

Printed in Switzerland
 Contents
Page
Introduction. ....................................................... 1

Scope and field of application ......................................... 1

References ......................................................... 1

Principle ........................................................... 1

Choice of illumination and viewing conditions ........................... 2

4.1 Smooth non-textured paint films. .................................. 2

iTeh STANDARD PREVIEW
4.2 Paint films with surface texture .................................... 2
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5 Choice of standard calorimetric observer and standard illuminant ........... 2

ISO 7724-2:1984 2
6 Apparatus .........................................................
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f1eeebaded71/iso-7724-2-1984
6.1 Spectrophotometer .............................................. 2

6.2 Abridged spectrophotometer ...................................... 3

6.3 Integrator.. .................................................... 3

6.4 Tristimulus calorimeter ........................................... 3

7 Sampling and preparation of test specimens. ............................ 3

8 Reflectance standards ............................................... 3

8.1 Primary standard ................................................ 3

8.2 Secondary standard ............................................. 4

8.3 Working standards .............................................. 4

9 Procedure .......................................................... 4

9.1 Method using a spectrophotometer ................................ 4

9.2 Method using an abridged spectrophotometer or tristimulus calorimeter . 6

IO Testreport ......................................................... 6

11 Bibliography ........................................................ 6

.. .
III
 iTeh This
STANDARD
page intentionally leftPREVIEW
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(standards.iteh.ai)
ISO 7724-2:1984
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f1eeebaded71/iso-7724-2-1984
INTERNATIONAL STANDARD IS0 7724/2-1984 (El

Paints and varnishes - Colorimetry -

Part 2 I Colour measurement

0 Introduction Luminescent paint films, transparent paint films and trans-

lucent paint films (for example for displays or lamp glass),
This International Standard, IS0 7724, comprises the following retroreflecting paint films (for example for traffic signs), and
parts : metallic paint films are outside the scope of this part of
IS0 7724.
Part 1 : Principles.
2 References
Part 2 : Colour measurement.
iTeh STANDARD I PREVIEW 1512, SO Paints and varnishes - Sampling.
Part 3 : Calculation of colour differences.
(standards.iteh.ai)
I S 0 15 13, Paints and varnishes - Examination and prepara tion
Parts 1, 2 and 3 of IS0 7724 describe methods for the in- of samples for testing.
strumental determination of the colour co-ordinates and ISOcolour
7724-2:1984
differences of paint films, ashttps://standards.iteh.ai/catalog/standards/sist/e94adb4e-c087-45ff-89e4-
required for such purposes as IS0 1514, Paints and varnishes - Standard panels for testing.
f1eeebaded71/iso-7724-2-1984
a) the objective description of colour differences between I SO 2808, Paints and varnishes - Determination of film
a test specimen (a test panel coated with a paint, or a thickness.
specimen from a painted article) and a reference specimen;
IS0 3534, Statistics - Vocabulary and symbols.
b) determining colour deviations in the production of
painted articles so that the results may be used for the con- IS0 5725, Precision of test methods - Determination of
repeatability and reproducibility by inter-laboratory tests.
trol or regulation of the process;
ISO 772411, Paints and varnishes - Colorimetry - Part 7 :
c) the objective description of changes in colour caused Principles.
by weathering and other chemical or physical influences;
IS0 7724/3, Paints and varnishes - Colorimetry - Part 3 :
d) the objective supervision of colour reference standards. Calculation of colour differences.

NOTE - Colour reference standards are subject to ageing, which may CIE Publication No. 15, Supplement No. 1, Special
lead in the course of time to pronounced changes in colour. High ac- metamerism index : Change in illuminan t.
curacy calorimetry is required for the timely detection of these
changes. This is of particular importance when ordering against such
reference standards.
3 Principle

Measurement of the tristimulus values XI,, YIO, ZIO by one of

1 Scope and field of application the following methods

This part of IS0 7724 describes the method for determining the - measurement of the spectral photometric characteristics
colour co-ordinates of paint films. The method is only ap- (spectral reflectances or spectral reflectance factors) of the
plicable to paint films that appear to be uniformly of one colour, paint film with a spectrophotometer and calculation of the
i.e. monochromatic, when examined with normal vision. Paint tristimulus values;
films that do not completely hide a non-transparent substrate
represent an opaque system and may be measured by using the - measurement of the tristimulus values with a
procedure described in this part of IS0 7724. tristimulus calorimeter.

1
 IS0 772412-1984 (E)

Calculation of the chromaticity co-ordinates xlo, ylo or the col- 4.2.2 Measurement excluding the specular reflection
our co-ordinates in the approximately uniform CIE 1976
(L*a*b*) colour space from the tristimulus values, as described For matt or low gloss specimens use the measuring conditions
in IS0 7724/l. 8/d or d/8 (with gloss trap for both). Alternatively, use the
measuring condition 45/O or O/45 if the specimen is turned dur-
ing the measurement, or the measuring condition 45/O if the
4 Choice of illumination and viewing specimen is illuminated toroidally or by two beams at 90’ to
conditions each other.

One of the measuring conditions for illumination and viewing NOTE - For paint films with surfaces that have high gloss and are tex-
specified in IS0 7724/l should be chosen taking into account tured, the measuring condition 8/d or d/8 (with gloss trap) and 45/O or
the surface texture, the reflection properties of the paint O/45 should not be used because random specularly reflected light may
reach the detector.
film tested and the information that is to be obtained by the
measurement.

5 Choice of standard calorimetric observer

4.1 Smooth non-textured paint films
and standard illuminant
All the measuring conditions specified in IS0 7724/l are suit-
The CIE 1964 supplementary standard calorimetric observer
able for determining the colour co-ordinates of smooth non-
and standard illuminant D65 should preferably be used.
textured paint films.

With high gloss specimens, results obtained under all For the calorimetric determination of a special metamerism
measuring conditions are comparable if the tristimulus values index (change in colour difference between two specimens
determined with an integrating sphere without gloss trap are caused by substituting a test illuminant for the reference illumi-
corrected for the surface reflection. nant, preferably D651)) standard illuminant A should be used as
the test illuminant.
NOTE - The surface reflection
specimen that is reflected (diffusely iTeh STANDARD
and specularly) TristimulusPREVIEW
is the part of the light falling on a
calorimeters of early design are provided with filters
at the surface;
that are only suitable for determining tristimulus values with the
another part is back-scattered by the pigments (volume reflection). The
surface reflectance (Fresnel reflectance)
between O” and 8O on paint films is approximately
(standards.iteh.ai)
for illumination
0,04.
CIE 1931 standard calorimetric system for standard illuminant C.
at incidence
If the calorimetric determination is based on the tristimulus
method, the use of this combination of standard calorimetric
For all other specimens the choice of measuring conditionsISO 7724-2:1984observer and standard illuminant should be allowed, but its use
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depends on whether the specular reflection is to be included in should be reported.
or excluded from the measurement (see IS0 7724/3). f1eeebaded71/iso-7724-2-1984

4.1 .l Measurement including the specular reflection 6 Apparatus

Use the measuring condition 8/d or d/8 (without gloss trap for
6.1 Spectrophotometer
both).

NOTE - If the gloss changes without a visually perceptible change in For high precision calorimetry, a single- or preferably a
colour, for example after weathering, the tristimulus values measured double-beam reflection spectrophotometer equipped with a
including the specular reflection will generally not be influenced. prism or grating monochromator and a photometer head that
satisfies the illumination and viewing conditions chosen as
described in clause 4 shall be used.
4.1.2 Measurement excluding the specular reflection

Use the measuring condition 8/d or d/8 (with gloss trap for Using these instruments, the repeatability with which spectral
both) or 45/O or O/45. reflectances or spectral reflectance factors can be measured
should be better than the larger of the following two values :
NOTE - If the gloss changes, the diffuse part of the surface reflection 0,2 % of the reading or 0,001 (absolute).
will change and consequently the tristimulus values measured ex-
cluding the specular reflection change too. The repeatability over long time interva Is should not exceed
these values by a factor of more than 3.
4.2 Paint films with surface texture
NOTE - For the purpose of this part of IS0 7724, the repeatability of
the measuring method is the value below which the absolute difference
4.2.1 Measurement including the specular reflection
between two single test results obtained for the same paint film under
the same conditions (same operator, same spectrophotometer, at a
For the spectral characterization of paint films with surface tex- short time interval) may be expected to lie with a 95 % probability. The
ture (for example textured finishes) use the measuring condi- repeatability is obtained by multiplying the standard deviation of the
tion 8/d or d/8 (without gloss trap for both). measuring method by the appropriate factor (see IS0 5725).

1) see CIE Publication No. 15, Supplement No. 1.

2
 Iso T724/2-1984 0

The accuracy should be better than the larger of the following in the wavelength range below 500 nm. The tristimulus value
two values : 0,5 % of the reading or 0,002 (absolute). XI0 is therefore formed by weighting the reflectance factors
measured with zX and rZ filters with various constants followed
NOTE - For the purpose of this part of IS0 7724, accuracy is the by addition.
closeness of agreement between the true value and the mean result
which would be obtained by applying the same method of calorimetry Because of the difficulties in fitting filters to the required
a very large number of times (see IS0 3534). parameters, tristimulus calorimeters are generally unsuitable
for measuring colour per se and should be restricted to measur-
If the calorimetric measurements are for the objective super- ing colour difference. Even in the latter use, however, there
vision of colour reference standards [clause 0, d)], a spec- may be difficulties in establishing compliance with a reference
trophotometer of the type described above should be used in colour if the standard and the specimen are metameric. Conse-
preference to the abridged type (6.2) or a tristimulus col- quently, tristimulus calorimeters are best restricted to applica-
orimeter (6.4). tions b) and c) described in clause 0.

The repeatability with which tristimulus values can be

62. Abridged spectrophotometer measured should be better than the higher of the following two
values : 0,2 % of the reading or 0,001 (absolute).
For the applications described in clause 0, a) to c), an abridged
spectrophotometer equipped with a photometer head that The accuracy can be worse than 1 %, depending on the
satisfies the illumination and viewing conditions chosen as lightness, and the shape of the reflectance curve.
described in clause 4 is sufficient, except when highly
chromatic paint films with steep spectral reflectance curves are
to be measured. Such an instrument is a photometer contain- 7 Sampling and preparation of test specimens
ing at least 16 interference filters distributed uniformly over the
wavelength range 400 to 700 nm and having a half-bandwidth For the applications described in clause 0 a) and c) take a
of 20 nm or less. representative sample of the paint to be tested as described in
iTeh STANDARD PREVIEW
For the short- and long-term repeatability, the same con ditions
IS0 1512.

as those defined for spectrophotometers in 6. 1 apply*

(standards.iteh.ai)
Examine and prepare the sample
IS0 1513.
for testing as described in

The accuracy should be better than the la rger of the fol lowing
two values : 1 % of the reading or 0,004 (absolute). ISO 7724-2:1984Prepare the test panels in accordance with IS0 1514. Apply the
coating, dry and, if necessary, condition the paint film as
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directed in the manufacturer’s instructions or as otherwise
f1eeebaded71/iso-7724-2-1984
6.3 Integrator agreed.

For weighting the measured spectral photometric characteristics NOTE - If the paint film is of reversible temperature-dependent
with the relative spectral power distribution of the standard colour, the temperature of the test specimen should be maintained at
illuminant SA and the colour-matching functions rIO( A ), 23 + 2 OC by appropriate measures (for example by the use of a
J$+ 2 ), ZJJ ) and the summation as described in IS0 7724/l, thermostatically controlled specimen holder). Paint films of irreversible
temperature-dependent colour should be postconditioned, until the
a computer facility with adequate storage may be used.
colour does not change any more. In the case of paint films that do not
completely hide the substrate, the colour depends on the colour of the
Abridged spectrophotometers and some automatic spec- substrate and the film thickness, which should be determined by one of
trophotometers embody electronic or mechanical integrators. the procedures described in IS0 2808.

From painted articles [application described in clause 0, b)] take

6.4 Tristimulus calorimeter test specimens that are representative of the surfaces to be
measured. If necessary, the number of specimens should be
The integration can also be performed optically with three agreed upon between the parties.
tristimulus filters which shall be constituted so that the
measurements appear in a simple linear relationship with the The paint film specimen shall be plane and clean. The di-
tristimulus values. Instruments of this category, which are mensions of the test specimen should be adequate to permit
termed tristimulus calorimeters, have to be equipped with a measurement with the size dimensions of the sample port of
photometer head that satisfies the illumination and viewing the instrument in use with the sample port being not less than
conditions chosen as described in clause 4. 10 mm in diameter.

The three filters have to be fitted with respect to their spectral

transmittance t-J A ), ryrC2 ), rZ( L ) to the colour-matching func- 8 Reflectance standards
tions, to the relative spectral power distribution of the standard
illuminant and of the light source of the instrument, and to the 8.1 Primary standard
sensitivities of the photoelectric detectors. With few excep-
tions the manufacturers of tristimulus calorimeters make no The primary standard for measuring the reflectance or reflec-
provision for close fitting. The tX filter completely absorbs light tance factor of the specimen is the perfect reflecting diffuser as

3
IS0 772412-1984 EI

recommended by CIE and defined as an ideal uniform diffuser A metal ring which will later serve as a frame for the tablets is
with a spectral reflectance equal to unity for all wavelengths. first closed at the bottom by a clean matt-ground glass plate
[see the note and the figure all. The ring and glass plate are
held together by a clamp (not shown). A weighed amount of
8.2 Secondary standard powder (1,65 g/cm3 tablet volume) is poured into the cylinder
inserted in the ring and the two sections of the powder press
are united so that the plunger enters the cylinder. Both sections
Because the primary standard cannot be realized in practice, a are now screwed together. To increase the density of the
secondary standard is needed with known spectral reflectances tablets, the top section should be tapped gently several times
that are as close as possible to those of the primary standard. with a rubber hammer. The top section can then be screwed in
further. Tapping and screwing should be repeated two or three
times until the powder fills only the conical portion of the ring.
8.2.1 Source
The top section with the plunger and cylinder should then be
removed and replaced by a lid. The press should now be turned
Compressed barium sulfate powder in tablet form is normally over [figure b)] and the clamp opened to allow the removal of
used as the secondary standard. The manufacturer of the the bottom section with the glass plate. The exposed surface of
barium sulfate powder used to prepare the tablets should state the tablet should come level with the front side of the ring,
the spectral reflectances @s/d( A ) Or spectral reflectance factors which abuts with the port of the photometer. The powder has
I?,,&) of the powder for various wavelengths. These now been compressed so tightly that the surface of the tablet
wavelengths shall be chosen so as to allow interpolation of can even be used in the perpendicular position or suspended
reflectances or reflectance factors to within an accuracy of without losing any grains of powder.
+ 0,001. The stated values shall refer to barium sulfate tablets
prepared by the described method and measured using an ab- NOTE - The surface of the glass plate that faces the powder is ground
solute measuring technique, i.e. related indirectly to the matt with abrasive (grain size about 0,3 pm) and afterwards etched
primary standard (see clause 11). with dilute hydrofluoric acid.

The powder shall be free of contaminants

for compressing. iTeh STANDARD PREVIEW
and shall be suitable The glass plate should be thoroughly
followed
cleaned in chromosulfuric acid
by rinsing first in distilled water and then in ethanol and
allowed to dry. For interim cleaning a wad of cotton wool impregnated
(standards.iteh.ai)
NOTE - The spectral reflectance @8/d ( A ) and spectral reflectance fac-
with ethanol is sufficient.

tor &&A ) of tablets made of barium sulfate powder almost coincide.

The extent to which the spectral reflectance factors &,&I. ISO 7724-2:1984
) and 8.3 Working standards
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Ro/~ (1) of tabl e t s made of barium sulfate powder agree has yet to be
determined. f1eeebaded71/iso-7724-2-1984
For routine measurements with an individual instrument it is
possible to use working standards with spectral reflectances
8.2.2 Preparation and checking that remain stable over a long period. These working standards
need not be uniform diffusers but shall be calibrated with the
aid of the barium sulfate standard and the instrument with
With a mechanical powder press used solely for this purpose, which they are used. They should be made from stable and
mould constant amounts of barium sulfate powder into tablets durable materials such as opal glasses, vitrolite or ceramic tiles.
having a minimum thickness of 5 mm and a density of 1,6 to The surface shall be polished to ease removal of surface con-
1,7 g/cm? The tablets shall exhibit a textureless, plane and tamination and for ease in cleaning.
matt surface. Clean the powder press carefully after each press-
ing operation as traces of residual powder may degrade the sur-
face quality of tablets. Tablets shall not be reprepared from the Neutral grey working standards should be used to check the
same powder sample. linearity of the photometric scale and to extend the
photometric range of the instrument, so that dark specimens
may be measured more reliably than would otherwise be
The repeatability of the reflectance of the secondary standard possible.
prepared according to this part of IS0 7724 shall be better than
0,2 % with a given batch of barium sulfate powder.
Checking the repeatability and the accuracy of the test method
can be carried out by using a number of spectrally selective
Reflectance standards prepared in this way, if carefully handled working standards.
and stored in a desiccator, can be used for 1 week. Care should
be taken to ensure that they are not exposed to ultraviolet
radiation (A < 270 nm) because this could induce a change in
9 Procedure
the spectral reflectances in the wavelength range below 450 nm
(see clause 11).
91. Method using a spectrophotometer
The following apparatus and procedure have proved suitable
for preparing barium sulfate standards. A schematic represen- The instrument shall be operated in accordance with the
tation of the powder press is shown in the figure. manufacturer’s instruction s.
 IS0 7724/2-1984 E)

Plunger
(Of non-abrasive material)

Cylinder
(of non-abrasive material)

Ring

Matt-ground
glass plate

t
f
cv
b-0
+
In

b)
iTeh STANDARD PREVIEW Ring

(standards.iteh.ai)
ISO 7724-2:1984
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Figure - Powder press for f1eeebaded71/iso-7724-2-1984
preparing barium sulfate (BaS04) reflectance standards

Adjust the photometric scale or the intensity measuring unit Adjust the slit width or the slit-width programme to a desirable
and the integrator, if provided. Set the zero point by use of a balance between spectral resolution and sensitivity with
highly efficient light trap at the sample port. Do not set the zero respect to the chosen wavelength interval (see next paragraph)
point by blocking the light beam. Set the upper end-point of and the lightness of the paint film that is to be measured. Select
the scale by an appropriate reflectance standard over the entire an appropriate recording speed.
visible wavelength range.
Measure in wavelength intervals AL = 10 nm over the spectral
Check the linearity of the photometric scale by using grey range 380 to 770 nm using monochromatic light with a half-
working standards with known spectral reflectances. intensity width of less than 10 nm. In special cases, such as
highly chromatic paint films with steep spectral reflectance
Calibrate the wavelength scale using cadmium or mercury curves, measure in 5 nm wavelength intervals using mono-
discharge lamps with sharp emission lines. chromatic light with a half-intensity width of less than 5 nm.

NOTE - Further instrumental errors can be avoided by the exclusion Dependent on the chosen measuring conditions, determine the
of diffused light (for example by using the appropriate stray light filter) spectral reflectances or the spectral reflectance factors, or
and by cleaning contaminated optical surfaces. when using an integrator, the tristimulus values and
chromaticity co-ordinates of the specimen in relation to the
Check whether the repeatability corresponds to the value given reflectance standard.
by the manufacturer of the instrument by using suitable spec-
trally selective working standards. To detect the introduction of an error into any measurement,
repeat each measurement. In the case of discrepancies larger
Periodically check again the linearity of the photometer scale, than the characteristic repeatability given by the instrument’s
the calibration of the wavelength scale, and repeatability, manufacturer, repeat the measurement several times and, if
dependent on the time and intensity of use of the instrument. necessary, eliminate the cause of the discrepancies.