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Glass: the material

In modern times glass is produced from pure silica. Its melting temperature is over 1700 C, which is too high for ancient manufacture. The addition of an alkali (soda or potash) lowers the temperature for melting. Lime was added to that mixture to stabilise it. The first Egyptian glass is therefore a soda-lime-silicate mixture.

Silica is the main constituent of the desert sand. Petrie believed that silica was obtained from quartz pebbles. Iron oxides and aluminium in glass suggest, that it was produced from impure sand and from pure silica.

The colour of glass produced in the ancient method would be a greenish or brownish tinge. Colourless glass can only be produced by addition of a decoloriser. There are few attestations for colourless glass in ancient Egypt, such as clear glass rods from Amarna (Nicholson/Henderson 2000: 197).

To produce a special colour colorants were used:

name colour    
cobalt (Co) blue    
copper turquoise-blue    
tin opaque/white    
Antimony (Sb) opaque    
Antimony (Sb) and iron yellow    
copper red difficult to produce turns over the years often to green



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