HISTORY OF GLASS

The Phoenicians are widely believed to have first made glass around 5000 BCE.
However, it wasn’t until the rise of the Roman Empire that glass started to be used
architecturally. Roman architects started using glass in windows to allow light into
buildings while protecting against the elements.
During the Middle Ages, stained glass became prominent in the design of
ecclesiastical structures. The vibrant colored glass used in cathedrals, such as
Chartres Cathedral in France and Sainte-Chapelle in Paris, not only served to bring
in light but also told religious narratives in a vivid and accessible visual format.
The Industrial Revolution in the 18th and 19th centuries marked a significant
turning point for the use of glass in architecture. Innovations in glass production,
including the cylinder and plate glass methods, allowed for the manufacture of larger,
clearer panes of glass.
Despite these developments, glass was mostly used in windows and decorative
elements until the 20th century. Modernism, emphasizing simplicity and function,
brought glass to the forefront. Architects like Ludwig Mies van der Rohe and Le
Corbusier embraced glass for its ability to blur the lines indoors and outdoors, using
it in curtain walls and large sliding doors. Buildings such as the Farnsworth House
and the Seagram Building epitomized this trend, transforming glass into a symbol of
modernity and progress.
Thus, the evolution of glass in architecture is a testament to technological
innovation and changing aesthetic preferences, demonstrating how a simple,
transparent material could revolutionize how we construct and perceive our built
environment.
Evolution into Modern Applications: Technological Advancements
In the contemporary world, advancements in technology and material science have
further broadened the application of glass in architecture, making it a fundamental
building material.
In the late 20th century, developments in manufacturing techniques allowed for
producing high-performance glass. This includes tempered and laminated glass,
which improves the safety and durability of glass installations, and low-emissivity
(low-e) glass, which improves energy efficiency by reflecting heat back into the
building.
The 21st century saw the advent of even more sophisticated glass
technologies. Smart glass, which changes its light transmission properties in
response to light, heat, or electricity, allows for dynamic control of light and
temperature within a building. This innovation is instrumental in creating adaptable,
energy-efficient buildings.
Moreover, advances in structural engineering and construction technology have
enabled the design of glass structures that were previously unimaginable. Today, we
see large-scale glass facades, structural glass walls, glass bridges, and even glass
floors.

GLASS
A hard brittle inorganic substance, ordinarily transparent or translucent; produced
by melting a mixture of silica, a flux and a stabilizer; while molten, may be blown,
drawn, rolled, pressed or cast to a variety of shapes. Glass has no definite melting
point. When it is heated, it first softens so that it can be bent. Further heating brings it
to the point when it becomes thick, syrupy liquid, a state in which it can be worked.
Finally at still higher temperatures it becomes a thin, watery liquid.

MANUFACTURING
1. SHEET GLASS (ordinary window glass)
The raw materials, sand, soda and limestone, are first ground to a fine state and
mixed in the proper proportions. This mixture, known as frit, is tied into the filling end
of a furnace and melted. Sometimes, cullet (broken glass) is also fed in to the
furnace. To form the glass into a sheet, it first passes from the furnace tank into a
drawing kiln, from here it is drawn up in the form of a sheet into a series of rollers.
These sheets of flat drawn glass are cooled slowly in a cooling chamber known as
annealing lehr. This type of glass is used where vision is required but where cost is
an important factor. The surface is good but never free from distortion as the two
surfaces of the sheet are not perfectly parallel.

2. PLATE GLASS
A high quality glass sheet of the same chemical composition as sheet glass. Plate
glass can be produced in thicknesses of from 1/8 to 1 1/4 in. although the special
thick glasses are usually cast rather than made by the continuous flow process. This
is special because both surfaces of the 100 in. wide ribbon of glass is simultaneously
grinded by a twin grinder unit, then when cut is polished with a jeweler's rouge to
give undistorted, clear vision and reflection.
3. FLOAT GLASS
A flat glass produced by a new process. It combines the fire-finish of sheet with
the perfect flatness of plate frit, the usual combination of raw materials is melted in
an oil or gas- fired furnace. The melted glass leaves the furnace and passes to a
float bath where it is supported on molten tin. Gravity keeps the liquid tin very flat,
and heat, applied from above melts out any irregularities in the glass, which is free to
conform to the perfectly flat tin. As the ribbon of glass passes through the float bath,
the heat is reduced until the glass is sufficiently hard to be fed on to the rollers of the
lehr without marking the undersurface. After leaving the lehr, the glass is cut into long
lengths. This process is suitable for thicknesses of 1/8, 3/16, and 1/4 in..
TYPES OF GLASS
1. REFLECTIVE GLASS
Used to control glare and reduce solar heat. It is the product of a glass-coating
process which is carried out in a large, rectangular vacuum chamber. The glass is
coated with micro-thin layers of metallic films which provide the performance
characteristics of the glass. It reduces solar heat gain by reflecting the sun's energy,
resulting in savings in initial and operating costs of air conditioning. The reduced light
transmission also diminishes interior glare and brightness.
Manufactured in two types, silver and gold, the glass can be specified in any one
of three nominal light transmittances of 8, 14, or 20 percent. A chrome coating
provides silvery outdoor reflections and creates a cool effect during the daytime,
while being neutrally transparent from the inside. At night, the glass "reverse" itself
by being transparent from the outside and semireflective from the inside.
2. ROLLED AND ROUGH CAST GLASS
Similar to the process of making plate glass. Glass of this type is used where clear
vision is not required, such as by factory roofs and walls, windows for halls and
staircases, sky- lights, and partitions in offices. Cast glass diffuses light, and
because of its low reflecting and absorption index, transmits 90 to 93 percent of light
rays striking it.
3. CATHEDRAL AND FIGURED GLASSES
Manufacturing is similar to rolled and rough cast glasses. However, they contain a
pattern or texture impressed usually on one surface by a patterned roller.
Thicknesses vary from 1/8 to 3/8 in. stock widths, from 40 to 50 in. with lengths up to
100 in. Example of pattern glass.
4. WIRED GLASS
Simply a rolled glass into which wire mesh is inserted during the process of
manufacture. The wire greatly increases the resistance to shattering through impact
wired glass as made in thicknesses of 7/32, 1/4 and 3/8 in. Stock widths 47 to 49 in.
and lengths up to 178 in. are produced.
5. HEAT-ABSORBING PLATE GLASS
This glass is made by adding ingredients to the mix used in making regular
slate glass so that the finished product is pale bluish-green or gray. Because of its
chemical composition, this glass absorbs a significant percentage of the sun's
radiant energy, thus reducing the build up of heat within the building. Its color and
the fact that it possesses lower light transmission than regular plate means that
glare and brightness in the room are reduced. This type of glass is quite widely used
for glazing in office buildings, school and hospitals.
6. TEMPERED PLATE GLASS
Three to five times as strong as regular plate of the same thickness --and area in
resisting compressive forces and fracture due to strain or thermal shock. It is made
by reheating and suddenly cooling plate glass. As a result, the outer surfaces are
under high compressive stress, while the center portion remains in tension. This
produces a condition that is highly resistant to breakage. Tempered plate glass is
used for swinging doors, sliding patio doors, windows in gymnasiums and
sports areas, skating rink enclosures, etc. Available in thicknesses of 1/4, 3/8,
1/2, 5/8, 3/4 and 1 in. Sizes of sheets vary with the thickness, but the normal
maximum size is 96 x 120 in.
7. VITREOUS COLORED PLATE
Polished plate glass can be heat-strengthened and coated on one side with
vitreous color which is fire-fused to the surface. The result is an opaque glass which
is widely used in curtain wall construction, store fronts, showrooms, laboratories and
industrial buildings. It should not be used as a glazing material but instead
should be applied against a backup of masonry or have some type of
insulative backing. Normal thickness is 1/4 in.; maxi- mum standard size, 72 x 120
in.
8. LAMINATED SAFETY GLASS (Bullet proofing)
Widely used in the automotive industry and transportation, but now finding some
uses in the building industry, like glass that can withstand firearm attack and
explosions. This is made of two thicknesses of plate or sheet glass bonded by a
thin, tough layer of polyvinyl butyral resin, a transparent plastic.
Safety glass made from sheet glass is produced in thicknesses of 9/64, 7/32,
15/64, and 1/4, maximum size of 7 sq. ft. for 9/64 thickness and 15 sq. ft. for the
rest.
Safety glass made from plate glass in produced in thicknesses of 1/4, 3/8, 1/2, 5/8,
3/4, 7/8 and 1 in. Units of all thicknesses are made in a miximum size of 72 x 138 in.
9. INSULATING GLASS
This consists of two sheets of plate or sheet glass, separated by an air space,
and joined around the edges to produce a hermitically sealed unit. There are three
methods of sealing and all these sealed units provide thermal insulation and
greatly restrict condensation. They reduce external noise but still permit the
entry of natural light.
CLASSIFICATION OF SHEET GLASS
1. Window glass-used for glazing windows doors and storm sash in residential
buildings where good light and vision are required at moderate cost. Thicknesses are
0.085 to 0.01 in. and 0.115 to 0.133 in.
2. Heavy sheet glass-used for glazing windows and doors where greater strength is
required but where slight distortion is not objectionable. Commonly used for display
cases, shelving, window ventilators furniture tops and jalousies made of two
thicknesses 3/6 and 7/32.
3. Picture glass-used for covering pictures, photographs, maps, charts projector
slides and instrument dials. Thickness vary from .043 to 0.053 in., 0.058 to 0.068 in.
and 0.07 το 0.08 in.

GLASS PRODUCTS
1. GLASS BLOCKS
Comparable in many ways to unit masonry but have the added feature of
transmitting light. They are made into two separate halves, which are heat-sealed
together to form a hollow unit with reasonably high thermal efficiency and sound
insulation. The edge surfaces of the block are coated with a gritty mortar bond.
Two types:
1. Functional blocks-direct or diffuse the daylight which passes through them to
improve the illumination of the building interior.
Three styles of functional blocks:
a. A light directing block directs incoming light upward toward the ceiling. Used
always above eye level.
b. A light diffusing block diffuses incoming light evenly throughout the interior of
the room.
c. General purposes block
2. Decorative or architectural glass -available in a wide range of styles and
patterns. These glass masonry units provide almost unlimited design versatility
when used in window, openings and facades, as interior walls and divider paneling.
Also used for ceilings. Method of attachment is by gluing to a plywood background
using rugby.
II. SOLID GLASS BRICK
Also made to admit light into a building, because of its solid construction, it offers
greater protection against vandalism than conventional window glass or glass
blocks. The ability of the brick is to allow undistorted passage of light.
Sizes 6 * 6 in., 8 * 8 in., 12 * 12 in., and 4 * 12 in.