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critical angle and more light will be totally reflected within the substance. For diamond n -- 2.42 and i = 24° 26';
for water n = 1.33 and i = 48° 36'. The low value of
critical
angle in diamond causes total reflection more easily and because of
repeated total reflection in cut stones, the brilliancy is very much
enhanced. The reverse is the
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case in quartz. -Repeated total reflection in cut stones with high dispersion tends to improve the fire.
Determination of refractive index
The
determination of refractive index is one of the most accurate and
easily applied tests to determine precious stones. There are three
methods: (1) Approximate immersion method, (2) Becke's method, and (3)
Refractometer method.
33
3
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