Cut From the Same Cloth

The Gemological Institute of America (GIA) and the American Gem Society (AGS) share the same parent—Robert M. Shipley—but over the last few years they have behaved like squabbling siblings on the issue of cut. The groups’ dueling gem labs treat cut very differently. AGS determines cut grades based on how a stone’s proportions compare to Marcel Tolkowsky’s “Ideal” model. GIA’s reports have no grade, because the institute feels cut is still not quantifiable ? which is what the disagreement is about.

GIA is in the middle of a massive, already nearly decade-long study on cut. When initial research found that no one set of proportions scored best for brilliance or fire, president Bill Boyajian declared he “could not recommend” the term “Ideal cut,” and compared it to prohibited terms like “blue-white.”

In an industry where monikers matter, those were fighting words.

But now both sides are saying strikingly similar things. AGS is overhauling its cut grading system and now favors the use of metrics for diamond properties like brilliance and fire—a stance in line with GIA’s research. Meanwhile, GIA—which has never graded cut—is moving toward its first-ever “cut classification system.”

Researchers acknowledge the gulf is narrowing. “There is more than one way to measure the speed of a car, but they are all pretty accurate,” GIA researcher Al Gilbertson said at a “Town Hall Meeting on Cut” at the recent AGS Conclave in Austin, Texas. “It certainly is possible—and probable—that if we both develop systems about what happens to a diamond, we will have very similar approaches.” AGS lab director Peter Yantzer agreed: “If we both do a thorough job, we will certainly end up in the same ballpark.”

Different strokes. Whether or not GIA and AGS arrive at similar conclusions, they are hardly twins on how they’re handling the issue. GIA is cautious and molasses-slow: Its cut assessment system was supposed to premiere in spring 2002, then spring 2003, and now ? well, suffice it to say that GIA no longer gives target dates. The delays stem from extensive consultations with the trade and in-the-field testing, such as the recent observation tests in Tucson. “Whatever we do, the trade has said, ‘Give us time to evaluate what this means to us as cutters, polishers, traders,’ ” Boyajian says. GIA also is genuinely committed to getting things right. “There could be a question that pops up two weeks from now that startles us,” Gilbertson points out.

At AGS, cut grading is central to the group’s identity, and the lab is sailing full speed ahead with its new cut grade and plans to evaluate fancy shapes. The lab wants to introduce ratings for princess and oval cuts by the end of the year. “We eventually expect to be able to issue a cut grade for any shape or facet style,” Yantzer says. GIA, on the other hand, won’t even consider evaluating fancies until it’s done with rounds.

AGS’s new “performance-based” system employs mathematically devised metrics that evaluate how different aspects of cut look to a person’s eyes. “The metrics are key to the entire project,” Yantzer says. “We are putting a lot of time into getting them right.”

The metrics will evaluate not only brilliance, fire, and scintillation but also “contrast,” which Yantzer calls “adjacent areas of light or darkness.” Yantzer believes contrast is crucial. “The thing with contrast is that some types enhance your perception of brilliance, and others decrease it. If you have a ‘nail-head’ that’s dark in the center surrounded by a Life Saver-shaped light area, that stone is ugly because of the bad distribution of contrast.”

The metrics are calculated by ray-tracing software originally developed by the optical industry. AGS’s current programs measure the angular spectrum of virtual stones. It’s developing new software to do the same for genuine stones, using a Sarin Dia-Mension machine and 3-D “skin models.” But the ultimate goal is software that uses digital photography to analyze how a stone handles light. “Measuring light is far more accurate than measuring angles and surfaces,” Yantzer says. “It tells you what’s really going on with that stone.”

All this has led AGS to one surprising conclusion: It will broaden its now-narrow definition of the best cut. “When all is said and done, we will likely have more opportunities to get AGS ‘zeroes,’ ” Yantzer says. But AGS is not abandoning the Tolkowsky gospel. “We have found some stones that perform the same as the Ideal,” Yantzer says. “But if you look at their proportions, they are not far from it. We’ve found that the farther you move away from Tolkowsky, the more you give something up, whether it’s fire, contrast, or brilliance. The Tolkowsky model is still a great model that’s withstood the test of time.”

Even so, the AGS lab may do things very differently in the future. “Our current system of proportion grading has its limitations,” Yantzer says. “Everyone knows that. But the technology required for a real performance-based approach has only been developed in the last few years. We just happen to be living in a great time when the technology’s available to really look at diamonds and find out what makes them beautiful.”