The structure of abraded glass surfaces

Abstract

The physical nature of the processes involved in the workshop operations of cutting and grinding are but little understood, such attention as these operations have received being mainly of an empirical nature. In the present paper some preliminary observations are recorded on the tooling of hard brittle substances where the phenomena may be expected to be simplest. Even here they are sufficiently complex. The primary object is to substitute the conception of a flaw- or fissure-complex for the current view of a hill-and-hollow structure, as characterising a ground surface in brittle materials. Part I. Section I describes observations on the flaws produced in glass by stationary, rolling and sliding spheres, and by glazier's diamonds and wheels. Section II deals with the structure of ground glass surfaces, applying the results of the previous section, and showing the surface to be a fissure-complex. Section III explains the double refraction observed by Twyman near the surface of these pieces of ground glass. Part II. Section I shows the enhanced solubility of ground surfaces in hydrofluoric acid, and suggests a value for the upper limit of the thickness of the flowed, or surfacetension, layer on polished glass. Section II describes the structure of polished surfaces of glass and similar materials as developed by etching, showing that mechanical abrasion is still active during polishing, and also confirming a low value for the thickness of the surface tension film.