[Jewelry making - Article 01309] - Re: [Orchid] R.I. testing?

[Bruce Holmgrain]

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    I am a little surprised that no one has pointed this out. 

    The Presidium Duo Tester doesn't measure the refractive index. It
    measures the "relative reflectivity" of a stone. While it is true
    that the reflectivity corresponds with  refractive index  of well
    polished stones with a flat surface,  there are  other related
    properties that would be better measured with a refractometer. Note
    double refraction and birefringence. Although it is a very
    interesting instrument, it is not "recommended" by the GIA. Perhaps
    because the relative reflectivity meter was first developed by the
    GIA's nemesis, Dr. Hanneman, a Phd that doesn't believe in paying an
    extraordinarily high price to do basic research that can be done on
    the cheap. A very interesting and affordable book can be found at

    http://www.mineralab.com/Gemology.htm 

Bruce D. Holmgrain
Goldwerx
http://www.goldwerx.com
guy AT goldwerx.com
JA Certified Master Benchjeweler, CAD/CAM Services

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