Some ill-made pieces are so utterly decomposed that they flake away, or fall to iridescent dust, at the lightest touch.
Others have suffered little from time or damp, but are streaky and full of bubbles.

A few are, however, perfectly homogenous and limpid.

Colourless glass was not esteemed by the Egyptians as it is by ourselves; whether opaque or transparent, they preferred it coloured.

The dyes were obtained by mixing metallic oxides with the ordinary ingredients; that is to say, copper and cobalt for the blues, copperas for the greens, manganese for the violets and browns, iron for the yellows, and lead or tin for the whites.
One variety of red contains 30 per cent of bronze, and becomes coated with verdegris if exposed to damp.

All this chemistry was empirical, and acquired by instinct.