Gems & Gemology, Fall 1982, Vol. 18, No. 3

Shadowing: A New Method of Image Enhancement for Gemological Microscopy

Peer Reviewed Article
John I. Koivula
The shadowing technique employs an opaque, black, nonreflecting light shield that is inserted gradually into the transmitted light path of a gemological microscope between the subject and the light source. Shadowing takes advantage of even very slight differences in refractive index between a gemstone host and its inclusions, casting shadows in certain areas of an inclusion scene and passing light to the microscope objectives in other areas of the image. Thus, shadowing produces a three-dimensionality that seems to lift the inclusion from its surroundings, revealing it in vivid contrast against the now-subdued background of the host. This increase in contrast adds much greater detail to growth zones, included crystals, color zones, and the like, thus greatly aiding the gemologist in his work with the microscope.

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