Properties of polishing media for precision optics

Abstract

The first theory concerning the pohshing of glass, which viewed polishing as an extension of the grinding process with finer abrasives, and the flow theory of Beilby, both stipulate purely hypothetically that the polishing grains should have a very high hardness. This hypothesis of high hardness of the polishing grains was so strongly supported by Smekal and Brüche in the 40's and 50's and by other scientists in the following years that it became dogma, i.e., a claim without proof, and has remained virtually universally accepted to this day. The results of the investigations of the present author have shown, however, that first, extra lattice defects in the crystalline oxides used as polishing agents are the primary characteristics that are responsible for the gripping of the grains during polishing and second, the hardness of the grains of the polishing agent must be lower than that of the material which is being polished. By and large these results have been ignored in the literature, because they are in Opposition to the dogma that the polishing agent must have a high hardness. Clear proof is presented in this paper that disproves the generally accepted hypothesis that polishing can be done with very fine grinding powder, and that the polishing agent must be harder than the glass which is to be polished. The properties of polishing agents for use in polishing for precision optics will be described on the basis of the theory of polishing agents containing lattice defects.