The glass is a mixture of a number of metallic silicates, one of which is usually that of an alkali metal. It is amorphous, transparent or translucent. It may also be considered as a solidified super-cooled solution of various metallic silicates having infinite viscosity.
For the purpose of classification, the glass may be grouped in to the following three categories.
(1) Soda-lime glass.
(2) Potash-lime glass.
(3) Potash-lead glass.