Learn how to determine a gem’s optic character with a refractometer and identify optical effects you may encounter during gem identification tests.
4 Minute Read
Before learning to determine optic character, be sure to review our article on using a refractometer to determine the RIs of faceted gems. You should be familiar with the instrument, procedures, and testing terminology.
There are five possible optic characters:
You can usually ascertain the optic character of a gem from the notes you took while testing it for double refraction. Interpret the results as follows.
The gem is uniaxial if both refractive indices (RIs) remain the same in each position or if one RI remained the same and the other varied. While doing this, you should have found a position with only one RI.
If you didn’t find a place where there was only one RI, you’ll have to test the stone again on another facet. The gem won’t rest on another facet as easily as it does on its table. You’ll have to hold the facet against the hemicylinder to do this. (Be very careful not to scratch your hemicylinder! Remember to shield it from extraneous light with your free hand, too).
If…
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Before learning to determine optic character, be sure to review our article on using a refractometer to determine the RIs of faceted gems. You should be familiar with the instrument, procedures, and testing terminology.
There are five possible optic characters:
You can usually ascertain the optic character of a gem from the notes you took while testing it for double refraction. Interpret the results as follows.
The gem is if both (RIs) remain the same in each position or if one RI remained the same and the other varied. While doing this, you should have found a position with only one RI.
If you didn’t find a place where there was only one RI, you’ll have to test the stone again on another facet. The gem won’t rest on another facet as easily as it does on its table. You’ll have to hold the facet against the hemicylinder to do this. (Be very careful not to scratch your hemicylinder! Remember to shield it from extraneous light with your free hand, too).
If…
Learn how to determine a gem’s optic character with a refractometer and identify optical effects you may encounter during gem identification tests.
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