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A new approach to the teaching and use of the refractometer
Darko B. Sturman
Sets of simple and reliable procedures for determining gemstone RIs on the refractometer have been assembled. 
They have been tested with 70 calculated patterns of movements of shadow edges during the rotation of a gemstone on the refractometer. Some procedures described in literature are shown to have been based on limited understanding of observations; this may lead to incorrect identifications which can cause confusion, loss of confidence, and ultimately may lead to a waste of teaching time. All observations on isotropic, anisotropic uniaxial and biaxial gemstones in every possible orientation of the optical elements and facets can be represented by seven patterns described in graphical form in Chart 1. The chart shows how to identify a pattern and what can be determined from each one. Interpretation of observed data and identification of a gemstone is made on a birefringence/RImax chart (Chart 2). Most known faceted gemstones with RIs < 1.8 are shown on a single two-page chart.
All the Journal articles placed online in 2010 will also be published in hard copy as a single Journal issue and sent to all paid-up Gem-A members early in 2011 as part of their 2010 subscription. Gem-A members may login to the membership area to view the full articles.
They have been tested with 70 calculated patterns of movements of shadow edges during the rotation of a gemstone on the refractometer. Some procedures described in literature are shown to have been based on limited understanding of observations; this may lead to incorrect identifications which can cause confusion, loss of confidence, and ultimately may lead to a waste of teaching time. All observations on isotropic, anisotropic uniaxial and biaxial gemstones in every possible orientation of the optical elements and facets can be represented by seven patterns described in graphical form in Chart 1. The chart shows how to identify a pattern and what can be determined from each one. Interpretation of observed data and identification of a gemstone is made on a birefringence/RImax chart (Chart 2). Most known faceted gemstones with RIs < 1.8 are shown on a single two-page chart.