Chapter 2 Materials and Equipment

The materials and equipment which are needed to produce the mirror are:

A 6-inch Pyrex mirror blank, from Corning Glass Co., Corning, N. Y. The sides of a Pyrex blank are tapered, giving to one surface a slightly larger diameter than the other. The larger surface is the one that is to be ground to curve for the mirror.

A 6-inch plate-glass disk, of a thickness at least 1/8 the diameter, from any plate-glass manufacturer. This is to serve as the tool. Abrasives (in the order in which they are to be used) : carborundum, No. 80, 8 ounces; No. 120, 3 ounces; No. 220 and No.400, 1 ounce each; alundum (fused aluminum oxide), No. 600 (or No. 2 garnet powder), ½ ounce; emery, No. 305 (or No. 8 garnet powder), ½ ounce.

Carborundum is a synthetic abrasive. The grains are separated into numbered sizes by passing them through a mesh of a. corresponding number of strands per inch. It is considerably harder than emery, and in the coarse-grain size is about four or five times as efficient.

Emery, a variety of corundum (native aluminum oxide), is a mineral deposit. It .is first broken up into powder form, and then graded by elutriation; that is, by repeatedly stirring in water and pouring or siphoning off the liquid, finer and finer settlings are obtained.

Garnet is also a mineral, and is treated in the same manner as emery. It is a cheaper product, but just as effective as an abrasive. Polishing agents: choice of fine optical rouge (red), cerium oxide, or Barnesite, 4 ounces. Red rouge (Fe2O3) is a product of iron oxide. This compound and to a lesser extent black rouge, another iron oxide, have for years been the only agents used in the polishing and figuring of fine optical surfaces.

materials and equipment continued