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Ancient glass techniques: cold-working and casting
For the Egyptians glass was 'stone of the kind that flows': in its hot and liquid state it is a flexible material that can be moulded or twisted into canes. Before the discovery of glass blowing about 50 BC, ingenious methods were used to form this remarkable substance.
Cold-working describes a great variety of processes in which glass is removed from the surface of an object held at room temperature with a scratching, grinding or chipping procedure. Decoration can be achieved by relatively deep cutting. Cold-working was also used to clean and smooth surfaces. Blanks could also be formed by cold-working; these need not bear any resemblance to the finished object.
Casting is used to produce a glass object in its final form: as a blank in anticipation of further hot-working or as a blank for cold-working. Soft glass was delivered to a refractory (heat-resistant) mould to give shape to the glass. Alternatively, a piece or pieces of cold glass were put in a mould and heated until the glass flowed to fill the void. Two or more contrasting glasses might be poured or melted, one on top of the other, in an open mould to produce blanks for cameo glass plaques and the like.