THE USE OF PEELS IN MICROSCOPICAL STUDY OF CLAY AGGREGATES

The technique of replica casting of ceramic materials and the various methods of mounting and examination are described. Co-ordination of optical properties of the peels and X-ray analysis is considered. The uses of peels in showing orientation of clays settled under gravitation and also effects of plastic deformation are discussed. HISTORY The peeling of pyroxylin or other films from the surfaces of petri-factions has long been used in the microscopical study of fossil plants. The history of the technique was summarized by Appel (1933). The technique was applied to soft ores by Appel (op. cit.) and to clays by Weatherhead (1940). Weatherhead noticed that detrital quartz-grains remained included in his micro-preparations, and this obser-vation led Williamson (1941) to use a comparable method for eluci-dating the effects of processing-operations (filter-pressing, casting, extrusion, mechanical spreading, etc.) on the arrangement of the non-plastic particles in electrical porcelain and other ceramic "bodies." These particles had been comminuted by ball-mills and other devices, and most of them were quartz or calcined flint as flattened chips and feldspar as cleavage-fragments. Because of their tendency to flatness they developed epositional or flow planar parallelisms in response to processing-operations, e.g., to filter-pressing or extrusion re-spectively. They were oriented within clay-aggregates where the basal planes of the clay-minerals were in some accord with the major surfaces of the included particles; thus a general planar parallelism tended to appear throughout the composite mass (Williamson, 1947