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By  , Wednesday, August 02, 2006

gem society,AGS

Early in 2005, the American Gem Society will revamp its cut-grading system for round brilliants.

The ratings will be based, in significant part, on assessment of a diamond's performance in the crucial areas of brilliance and fire. The ratings also represent a major redefinition of the round-brilliant cutting style with which AGS has been synonymous since the 1940s: the American Ideal Cut.

For more than a decade, AGS and the Gemological Institute of America have been locked in a ferocious gemological battle over use of the phrase "ideal cut." In 1997, GIA's president Bill Boyajian issued a public statement calling for abolition of the term "ideal" as an adjective because it unfairly implied the supremacy of stones cut to proportions espoused by Marcel Tolkowsky in 1919. Boyajian claimed that GIA's studies of diamond brilliance proved that Tolkowsky's recommended table percentage, as well as crown and pavilion angles, were only one set of proportions that produced optimal brilliance in diamonds.

Hence they were hardly ideal.

AGS's new cut-grade system is an artful end-run around GIA criticism. It allows AGS to continue to use and be identified with the term "ideal," all the while showing it is mindful of GIA concerns. Using its new system, AGS says stones with 37% more combinations of table percentages, plus crown and pavilion angles, will be eligible for its much-esteemed top cut grade of "'O' Ideal Cut."

By expanding the term "ideal" to include stones with, for example, tables up to 61%, AGS feels it can continue to use it. The group says it can do so because grading is no longer based merely on measurement of proportions but also measurement of performance. Stones lacking stellar brilliance and fire will be disqualified for top grades. Here's how AGS will rate stones.

First, diamonds will be scanned by a Sarin machine for detailed readings of all angles. Then Sarin measurements will be fed into a computer with special software that creates a 3-D model of the diamond in cyberspace. This virtual diamond will then be subjected to ray tracing analysis for both brilliance and fire.

Based on these readings, a stone will be assigned a grade of Zero for best to 10 for worst. Those round brilliants judged 'best' will be considered "ideal."

The ball - a cannonball, perhaps - is now in GIA's court.


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