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The Journal of Gemmology 2010
Use of the polarizing filter on the refractometer in determinations of the optic sign or optic character of a gemstone
Darko B. Sturman and Duncan Parker FGA FCGmA
Calculated patterns of movement of shadow edges during observations on the refractometer were used to modify procedures for the use of the polarizing filter in determination of the optic sign and the optic character. New procedures are presented in graphic form in three charts. Eight calculated patterns to suggest these procedures are presented in the Appendix.
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.