September 13, 2004
AGS Unveils Cut Grade Plans
American Gem Society Laboratories (AGSL) lab reports will include new and improved cut grades for round diamonds starting in the first quarter of 2005. For the first time, AGS will also offer a cut grade for princess cut diamonds. Round and princess cut diamonds constitute the most popular diamond cuts among U.S. jewelers and account for a majority of diamond sales.
"The format of the lab reports will remain the same as in the past, with final diamond grades listed on the familiar scale of 0 to 10," says Peter Yantzer, AGSL executive director. "The changes incorporate the findings from our most advanced cut grade research on round brilliant diamonds and princess cut diamonds. The bottom line is that it provides retailers with greater assurance about the solidity of their cut grade. It also provides them with additional choices." Further good news for cutters and retailers is that the research findings enlarge by 37% the potential field of candidates for diamonds that can achieve a "0" grade (AGSL's highest cut grade for a diamond). The addition of the princess cut grade also increases a retailer's selling opportunities.
Ruth Batson, executive director and CEO of AGS, says the incontrovertible nature of AGS findings also protects the consumer, which is one of the basic pillars of the American Gem Society.
AGS fancy cut-grading research is composed of an AGS task force as well as outside industry experts and physicists. It started almost five years ago, and is funded in part by JCK magazine.
Larger Field of Candidates
"We want retailers to understand that the known format of the reports supported by our findings will provide a very positive opportunity for retailers," Batson says. "The research is reassuring and exhilarating in that our methodology provides great promise for other fancy cut grades in the not too distant future," Yantzer adds.
AGSL research incorporates three dimensional imaging and optical [light] ray tracing to evaluate cut. AGS says their conclusions help underscore Marcel Tolkowsky's own two dimensional diamond math based modeling, (Diamond Design) postulated just over a century ago. His work centered on round brilliant diamonds with 53% tables; 60-61% total depth; 16.2% crown height; 43.1% pavilion depth and girdle thicknesses of 0.7 to 1.7%. Crown angles of 34 degrees, 30' and pavilion angles of 40 degrees, 45'. These factors, he theorized, were necessary to make an optimum cut. Since his day, cutters have used and modified Tolkowsky's guidelines to suit their needs, mostly by lengthening or shortening lower girdle facets, and by enlarging (or decreasing) the table facet percentage.
"Tolkowsky was right, really," Yantzer says. He notes that Tolkowsky's theoretical diamond sits
smack in the middle of AGS' list of potential candidates. Three dimensional research and optical ray tracing was not available to Tolkowsky, however, and AGS research finds that diamonds with tables between 47% and 57% can also achieve AGS "0" grades with varying degrees of success, depending on what compensations were made to other aspects of the diamonds' cut angles to ensure proper light return, or brilliance. This discovery allows cutters and retailers more flexibility to adjust for societal and cultural preferences (some people prefer more fire, others more scintillation.)
AGS also says that it will soon make ray-tracing software available to member retailers who want to better understand the mathematical reasons for light return, as well as see how a given diamond performs. The metrics are repeatable and accurate, taking into account light dispersion, leakage, direction of light return, brightness, contrast and fire, among other factors.
For retailers, the findings translate to added sales of AGS "0" diamonds whose footprint or outline may be the same, yet in which the weights are considerably different. "For example, a 6mm stone may weigh either 1.40-ct or 2.00-ct, and because of cost considerations, a customer may want to choose the 1.40-ct stone," Yantzer explains.
Robert Weldon, G.G.