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Dispersion Staining, Objective Stop
In the 1950's Yu. A. Cherkasov began working with optical
screens at the objective back focal plane to
improve on the techniques developed by Wright. He refered to this technique
as Focal Screening. His work was first
published in English in 1960 (Internation Geological Review, vol.2). This
technique was further developed and promoted by
Walter McCrone and K. M. Brown of McCrone Research Institute in the 1960's
and 1970's. This is the most common form of
dispersion staining used today, though not always the most appropriate. It
severely impairs image quality though the colors
can be quite vivid. There are three different types of objective stops that
can be used. They are the central stop, the
oblique stop, and the annular stop. The first two are the most useful.
Match at 650 nanometers wavelength, Amosite Asbestos Perpendicular to length
Match at 440 nanometers wavelength, Amosite Asbestos Parallel to length
Match at 490 nanometers wavelength
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