A1. Basic Glassmaking

Glassmaking involves three basic steps: batching, melting, and forming. Batching is the preparation of a mixture of sand and stabilizing oxides, all in fine granular form. Melting involves the heating of the mixture to change it into a liquid and to further homogenize the various ingredients. Forming is the creation of useful objects or products from the molten mixture before it has completely solidified. The process can be carried out on either a batch or continuous-flow basis, the latter being used in mass production situations. Normally, forming operations take place immediately after the basic glassmaking, with the molten glass being cooled to increase its viscosity for forming.

There are many different kinds of glass. Soda lime glass is used for bottles, window panes and drinking glasses. Lead-alkali silicate glass has lead oxide in place of much of the calcined lime and is used for highly worked shapes including decorative glassware ("lead crystal") that is engraved. Borosilicate glasses, which contain boric oxide, are used when chemical and temperature change resistance is important, for example, in pharmaceutical containers, chemical process components and lamp envelopes. Aluminosilicate glasses are used where high temperature conditions exist. Several other mixtures may be used when optical properties are important.