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Retrieved from Dr. Hanneman's vault !!! - the famous Diamond Eye Reflectivity Meter. Dating to the 1970's, when the simulant known as Cubic Zirconia was introduced, this was among the the original "Diamond Testers" before thermal conductivity probes came on the market. But the Diamond Eye still has relevance and purpose today, re-configured by Dr. Hanneman as a Relative Reflectivity Meter, using the Auxilliary Scale (see photo), along with his customized testing method.
Just calibrate the meter with a reference gem of your choosing (Spinel, in this example), where the needle on the meter points to the bold, vertical hash line at the center of the scale. Now measure an unknown gem, and note the relative needle position. If it points to the left of the Spinel reference mark, then your unknown gem has a reflectivity value (and refractive index) less than Spinel. Or, if the needle points higher up the scale than the Spinel reference position, then your gem has a greater reflective and refractive index value than Spinel.
To further narrow down the identity of your unknown gem, you can establish other reference points along the auxilliary scale using a low reflective gem such as Quartz (well to the left of your Spinel mark), along with a high reflective gem such as CZ (well to the right end of the scale).
The main photo of the Diamond Eye shows the rotary Calibration knob at the left, the Gemstone Platform at the lower center, surrounding the Optical Eye, and the red Test button at the right. To measure a gem, just center it, table facet down, over the Optical Eye, then shield out ambient light with your cupped hand or other cover, and then press the red Test button, which triggers the movement of the needle up to its relative Reflectivity value.
The Diamond Eye is an affordable alternative to other Reflectivity Meters and Refractometers. And you have to love its retro design and look!
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After using a reference stone, a rhodolite garnet, it was easy to quickly separate higher and
lower RI stones. I put the different stones in a group not seeing what they were, and quickly
making a note about where it registered gave me enough information to deduce what the stone was. It's nice to be able to separate stones with lower RI than just diamond and its counterparts. Thank you Dr. Hanneman! Jeff Dolson on Feb 16th 2017