A Gemological Refractometer is your primary and most powerful tool in gemstone identification. As with any typical critical angle refractometer, it will measure the Refractive Index of faceted stones, transparent to near opaque, whether loose or mounted (in most cases), up to an R. I. value of 1.81.
We are proud to feature here the respected Gem-A brand of Refractometer, which is Professional grade, as seen in the photo at left. This model is sturdily built and of the finest quality. It includes an integrated Monochromatic Filter precluding the need for a special monochromatic illuminating light. The unit's eyepiece includes a Polarizing Filter for precise measurement of Birefringence, and adjusts telescopically for the clearest image. Your refractometer kit also includes a bottle of Refractive Index Liquid with a matching R.I. value of 1.81 (see photo at right).
To use the refractometer, open the lid, then place a small amount of R.I. fluid on the refractometer's measuring glass using the bottle's built-in dropper. This fluid is necessary to create an optical contact between the glass and the gemstone. Then place a flat polished facet of your stone on the measuring glass and close the lid of the refractometer to shield out extraneous light. Then present a light source to the back of the instrument, and look through the eyepiece and read the scale at the point of division between the lighted portion and the shadowed portion created by the critical angle of the particular gemstone.
If the gemstone is doubly refractive, best seen by rotating the polarizing filter as you view the scale, you will see 2 shadow lines, the numerical difference between them equating to that stone's birefringence. As an example, the stylized drawing of the refractometer scale at left shows an R.I. value of 1.654 to 1.689 and thus Birefringence of .035, probably identifying this stone as Peridot.
This refractometer is from the Gemological Association of Great Britain. Dimensions are 4.5" Deep x 1.3" Wide x 2.6" High. It comes in a beautiful, protective Carrying Case (see photo at right), along with instructions in English.
This model is also suited for using the "Spot" or "Distant Vision" method for measuring cabochons and small, faceted stones.
We also include a handy laminated chart listing both R.I. and Birefringence values for
popular gemstones (see photo below).
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