Dueling Cut Grades

The American Gem Society and the Gemological Institute of America are in a showdown over which organization has the best system for grading diamond cut. The latest shootout took place in August at the annual midyear conference of the National Association of Jewelry Appraisers. In the opening session of a daylong program called “Diamond Dazzle or Diamond Daze,” AGS director Peter Yantzer provided evidence that his organization's system is the most exacting, while GIA's Patrick Ball and Al Gilbertson showed why theirs is the easiest to use. Yantzer discussed the science of ray tracing and demonstrated how images from the angular spectrum evaluation tool (ASET) relate to the AGS cut grade. Ball and Gilbertson, using knowledge from ray-tracing computer modeling as well as 70,000 human paired- comparison observations, said their grading scale allows for easy calculations based on Sari

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