Egyptian glassmakers melted glass in open fireplaces
in clay bowls. Burnt pieces were thrown incandescent into the water, where they
cracked. These fragments, the so-called frits, were ground by the millstones to
dust and melted again.
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| Glass. The second half of the 4th century. |
The medieval melting furnace (“goot”) was a low,
wood-burning vault, where glass melted in clay pots. Laid out only of stones
and alumina, it could not stand for a long time, but the supply of firewood was
not enough for a long time. Therefore, when the forest around the goot was cut
down, it was transferred to a new place, where the forest was still in
abundance.
Another furnace, usually connected to the smelter, was
an annealing furnace - for quenching, where the finished product was heated
almost to the glass softening point, and then quickly cooled to compensate for
the stresses in the glass (to prevent crystallization).
In this form, the glass melting furnace lasted until
the end of the XVII century. The shortage of firewood, especially in England,
forced in the XVII century to convert some goots to coal. Sulfur dioxide volatilized
from coal and stained glass yellow, so the British began to melt glass in
closed, covered pots. This melting process was difficult and slowed down, it
was necessary to prepare the charge not so solid. Nevertheless, already at the
end of the XVIII century, the use of coal becomes predominant.
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| Modern Colored Glass |
