Architectural Glass

Most glass is a mixture of silica obtained from beds of fine sand or from pulverized sand- stone;an alkali to lower the melting point,usually a form of soda or,for finer glass, potash lime as a stabilizer; and cullet (waste glass) to assist in melting the mixture.
The properties of glass are varied by adding other substances, commonly in the form of oxides, e.g., lead, for brilliance and weight; boron, for thermal and electrical resistance; barium, to increase the refractive index, as in optical glass; cerium, to absorb infrared rays; metallic oxides, to impart color; and manganese, for decolorizing.