GIA's President Bill Boyajian Offers Information On Cut Grading

In reference to articles and correspondence in recent issues about the dilemma of proportion grading the Tolkowsky model alone. I would like to offer the following thoughts. Conclusions about cut cannot and must not be drawn from individual measurements any more than the outcome of a football game can be drawn from any one play. Moreover, GIA's three dimensional computer ray tracing research to date indicates a multiplicity of proportion options yielding significantly beautiful stones - certainly no less beautiful than a Tolkowsky proportioned round brilliant- that in many cases are more attractive to many eyes.

One example discovered in our investigation of modeling proportions of a round brilliant cut diamond revealed that, by our method of calculating brilliance, a 59 percent table is more brilliant than a 53 percent table, which was defined by Tolkowsky as "ideal" This calculation was based on maintaining all other angles defined by Tolkowsky. Perhaps more important, it appears that brilliancy alone can also be affected by the interrelationship between different sets of angles from the crown and the pavilion. Even if the diamond the smaller table happens to show more fire, we question the sensibility of dictating to consumers that a diamond with a larger appearance and more brilliance is worth less than one with more fire. The results of our preliminary research are currently in preparation for publishing in our quarterly journal, Gems and Gemology.

This leads to a second thought regarding the reporting of cut on diamond grading reports and the use of optically sophisticated equipment in that process. It is a further trap for the trade to adopt measurement parameters that are altogether too strict in their reporting. Anyone can print out a host of dimensions from today’s non contact optical measuring devices and appear to be doing the public a great service. While anyone rushes to be the first to carve a niche in the marketplace for diamond grading and cut analysis, we caution trades people to avoid embracing unproved standards that may create a public backlash rather than a diamond boon. I

t took decades of extensive research using high technology to bring the industry to a more modern and scientific understanding of proportion considerations in a round brilliant cut diamond. While I doubt that it will take as long to further our knowledge of cut, I fear that the premature use of information without a thorough understanding of its scientific basis and practical implications is a bubble waiting to burst.

WILLIAM E. BOYAJIAN
PRESIDENT
GEMOLOGICAL INSTITUTE OF AMERICA