If oxide of copper is added to a glass mixture containing a strong reducing agent, a glass is produced which when first taken from the crucible is colourless but on being reheated develops a deep crimson - ruby colour.
During the process of manipulation, whether on the chair or whilst the glass is being reheated, the rod must be constantly and gently trundled to prevent the collapse of the bulb or vessel.
Another species of glass manufacture in which the Egyptians would appear to have been peculiarly skilled is the so-called mosaic glass, formed by the union of rods of various colours in such a manner as to form a pattern; the rod so formed was then reheated and drawn out until reduced to a very small size, z sq.
The plaques thus formed could be reheated and fashioned into the bases of bowls and drinking vessels.
The former was made, as described by Theophilus, from cylinders, which were split, reheated and flattened into square sheets.
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