Composition and Solid-state Structure

Characterization of a surface includes not only topography but chemical composition and solid-state structure. An experieneed mieroscopist can identify many microscopic objects by shape, size, surfaee detail, eolor, luster, etc. 

Unfortunately, it is difficult to describe a surface so that it is recognizable by someone else. Useful descriptive terms for surfaces include angular, cemented, cracked, cratered, dimpled, dmsy, laminar, orange peel, pitted, porous, reticulated, smooth, striated, and valleyed. 

A microscopist should recognize a paper as rag, mechanical coniferous, chemical nonconiferous, or as combinations of these by studying the paper surface. He/she should recognize such surface features on small particles as scales on wool, crossover marks on silk, striations on viscose rayon, twin bands or calcite, melt and crystal patterns on micrometeorites, lamellar steps on mica, the fibrous structure of incinerated wood sawdust, etc., which help identify that substance. 

Measurements of reflectance on polished surfaces can be used to calculate refractive indices of transparent substances and to give specific reflectance data for opaque substances, methods are discussed in detail by Cameron (1969). Reflectance and microhardness data are tabulated by Bowie et al. (1958) in a system for mineral identification. 

Staining a surface, either chemically or optically, helps differentiate parts of a composite surface and identify the various phases. A variety of stains are available for diverse surfaces. Mineral sections can be etched with hydrofluoric acid then stained with Na3Co(N02)e to differentiate quartz (unetched), feldspars (etched but unstained), and potassium feldspars (etched and stained yellow). Paper surfaces can be stained with Harzberg stain (Calkin, 1934) to differentiate lignified cellulose e.g., straw, manilla, and mechanical wood pulp [yellow or yellow green]) from purified cellulose e.g., chemical wood pulp, bleached straw, or manilla [blue or blue violet]) or pure cellulose e.g., cotton or linen [wine red]). Isings (1961) selectively stains unsaturated elastomers with osmium tetroxide. 

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