In identifying a gemstone, the refractive index of the stone is one of the important characters. When the refractive index is in the range over the ordinary refractometer, we have to identify the stone by other characters. Since the refractive index is theoretically a function of reflective index, an instrument is designed to measure high refractive index using the value of reflectivity. Measurements on several gemstones with higher refractive index by this instrument showed that we could identify them, provided that stones have the refractive index over 1.81. This instrument will be useful for identifying high refractive gemstones.

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Natural II a-type diamond has a high optical transmission ratio from ultraviolet (225nm) to infrared (13μm), and a study on the optical properties of diamond films synthesized by microwave plasma CVD was accordingly carried out with a view to applying the synthesized diamond films in optical parts.
Diamond films were synthesized from CH₄-H₂ and CO-H₂ reaction gas systems on quartz substrates. Film thickness was a uniform 1μm.
Raman spectroscopy showed that carbon source concentrations that did not contain non-diamond elements (amorphous carbon etc.) in the films was higher for the CO-H₂ system than for the CH₄-H₂ system. This was because the etching rate of oxygen to carbon is higher than that of hydrogen.
In terms of optical properties, the transmission ratio of diamond films containing minute amount of non-diamond elements was about 50%, and was uniform from 240nm to 2600nm. But as the amount of non-diamond elements increased, the transmission ratio at 250nm and 500nm decreased.
The transmission ratio of the diamond films in the ultraviolet and visible ranges depended on the quantity of non-diamond elements in the films.

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Diamond anvil is an essential item for high-pressure experiment. We do a stocking of a natural diamond rough stone to produce the diamond anvil. We want to tell that difficulty of the stocking. In addition, we introduce laser machines and try for improvement of the cutting accuracy every day.

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In this paper, we introduce our researches on rendering gems by computer graphics (CG). First, the principles of computer graphics and our purposes on researches on gem image generation are described. Then we show our results of researches on generation of images of brilliant cut diamond and gems with asterism. Produced images and some analysis results are given.

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