Observations on Glass Polishing

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Abstract
Despite the various theories of the mechanism of glass polishing that have been proposed over the years, there can be little doubt that both chemical and mechanical interactions between the glass surface, the polishing agent, water, and the polishing pad take place. In the following discussion some observations supporting this theory will be presented as well as some other observations of interest to the practicing optician. Before proceeding, however, a word about the measurement of polishing activity is in order. As described elsewhere (1), we subscribe to the belief that polishing of glass involves stock removal and that the stock removal rate as determined by weight is the same whether measured on a fine-ground or on a polished surface. This conviction is based on experiments in which previously fine-ground glass blanks were polished in a sphere machine and corresponding weight loss, thickness loss, and light transmittance measurements were determined as polishing progressed. It is significant that when such observations are made, the weight loss is linear with respect to time; that it remains so during the time the surface is progressing from the ground to the polished state; and that it remains linear after the polished state is reached. On the other hand, the thickness loss as measured with a thickness gauge has a steeper initial slope that decreases with time and finally runs parallel to the weight loss slope after the surface is completely polished. The transmittance measurements increase rapidly to a value of about 90% of that of a previously polished surface used as a standard, and then approach the polished surface value of 100% in a nonlinear manner. Accordingly, these observations and many similar ones made over the years justify using weight loss as a measure of polishing rate, although for purposes of comparison (convenience), we convert the weight loss to a thickness loss by dividing the measured weight loss by the density and the surface area of the glass blank.

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