Glass - Early
The basic components of glass are silica (sand), soda (or potash) and lime. The silica, when melted by heat, forms the glass; the soda acts as a flux to allow the glass to melt at a lower temperature; and the lime is a stabiliser.
The combination can be modified. Lead oxide used as the flux makes the glass less brittle and more stable but harder to work when hot. Various oxides and silicates add colour. Tin oxide makes the glass opaque.
By 2000BC, Egyptian craftsman were skilled at making glass articles. They developed four techniques:
- Glass jars were moulded around cores of mud or straw. This technique was common by the 18th Dynasty (1567-1320 BC). This technique can produce objects formed from bands of coloured glass.
- Glass was cooled and then carved and polished to the desired shape. The glass was often coloured to resemble a semi-precious stone. This technique was known for many centuries but became widespread in the eighth century BC.
- Molten glass was poured into a mould. Sometimes a ground paste of glass was poured into a mould and then melted.
- Small pieces of glass were laid together into a mould and fused together by firing.
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