A method is presented for the determination of high refractive indices in gemstones such as diamond and diamond substitutes, above the limit of 1.8 that can be measured by a conventional refractometer.
Measurement requires access to only a microscopically small area of a facet, with an accuracy of 60.05 in refractive index. The principle is to determine the Brewster angle, as in existing instruments, but using a polarizing reflection microscope. The result is obtained by examination of the back focal plane of an oil-immersion objective and can be recorded in an image. A patent is being sought for the method.
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