TABLE OF CONTENTS Although glasses can be made by a wide variety of methods, the vast majority are still produced by melting of batch components at an elevated temperature. This procedure always involves the selection of raw materials, calculation of the relative proportions of each to use in the batch, and weighing and mixing these materials to provide a homogeneous starting material. During the initial heating process, these raw materials undergo a series of chemical and physical changes to produce the melt. Conversion of this melt to a homogeneous liquid may require further processing, including the removal of any unmelted batch remnants, impurities, and bubbles. Production of commercial products requires forming of specific shapes, as well as heat treatments to remove stresses generated during the cooling process, or to produce glasses strengthened by thermal tempering.
In general, glasses are either produced from high quality, chemically-pure components, or from a mixture of far less pure minerals. Research specimens, optical glasses, and many glasses used for low volume, high technology applications are produced using those chemicals we might routinely encounter in any chemical laboratory. Bulk commercial products, on the other hand, are produced from minerals, which typically have names and compositions which are not familiar to the novice. The names of many of these minerals and their compositions are listed in Table 3.1. Gravimetric factors, which allow calculation of the yield of the desired glass component for each weight unit of raw material, are also listed in this table.
