Historical records from
Mesopotamia give formulae for glass making. Glass objects were rare
and thus very valuable till 1500 BC. Initially craftsmen in
Mesopotamia heated the required mixture, formed glass and allowed it
to cool. It was then shaped using abrasive tools. Continuous
experiments with glass making would have led to the inevitable
discovery that glass could be easily shaped when the mixture was
still hot. Once this was known there cropped up innumerable methods
for making specific shapes. For making a hollow vessel, a lump of
clay attached to the end of a rod was dipped into the molten glass
mixture. When cool, the clay was scraped away from inside the
vessel. Another method was to produce glass rods, reheat them and
coil them around a clay core. These would then be heated again and
rolled to and for on a stone slab in order to get a very smooth
Impurities present in
the mixture would give interesting colors to the final product. The presence of iron compounds would give a green or amber
while something else could render the glass opaque. This gave birth
to the idea of adding copper to the mixture to get a blue coloring.
Streaks of different color would be woven into the outer surface by
rolling them on after reheating.
In the second century
BC, glass blowing began to be practiced in the eastern Mediterranean
regions. The glass mixture would be gathered at the end of a long
iron tube and then blown into thin-walled balloon shapes. These
would then be shaped as desired on being heated again. An
improvement on this method was the use of moulds. The glass mixture
would be blown into a mould and after cooling would be removed from
the mould. The next feature added to glass items was achieving the
exact color and translucency desired. Cobalt was used for blue,
magnesium for purple, copper for turquoise and green and so on.
The next natural value
addition was making the glass items decorative. Different techniques
were used to give breathtaking effects on glassware. It was also
discovered that spinning the blow iron in a particular way resulted
in the formation of a thin sheet of glass, which was then used to
make glass windows. Many different techniques of glassmaking
evolved during the Roman Empire and it slowly spread into Europe
where it evolved further. In the late Middle Ages, Venice was
renowned for its glassware.
The various types of
glass made are soda glass; flint glass, used in cut-crystal ware;
optical glass; stained glass; heat resistant glass; fiberglass, etc.
Blown glass is used for
the making of expensive crafted glass and also for the manufacture
of light bulbs and bottles. Items like jam jars, vases, etc., are
made by pressing molten glass into moulds. Sheet glass for windows
is now made by putting the molten glass through rollers. Fiberglass
that is so widely used now is made from fine glass fibers.