After 16 years of research and more than 70,000 visual observations of 2,000-plus diamonds, GIA has concluded that there are many ways to cut a round brilliant diamond to give it a pleasing overall appearance, said GIA Gem Laboratory representatives during a presentation in Tucson, Feb. 6.

Held in conjunction with the American Gem Trade Association’s GemFair, the seminar was presented by GIA Research Associate Al Gilbertson and Manager of Laboratory Communications Barak Green. They covered the foundations and progression of the Institute’s ongoing cut study.

After initial exploratory testing, GIA researchers compared their computer-modeled predictions of brightness and fire with thousands of observations from individuals in all levels of the diamond trade (including consumers). From this, Gilbertson said, they created and tested additional metrics, eventually using the observations to refine brightness and fire metrics. Researchers were subsequently able to determine thresholds at which people usually saw differences in appearance, as well as isolate other significant aspects of a diamond’s face-up appearance (those related to scintillation) that could then be predicted through additional calculations and formulas based on the diamond’s proportions.

“We combined the findings of our observation testing and trade discussions with the prediction and assessment capabilities of our brightness and fire metrics,” Green continued, noting the importance of standard lighting and viewing environments for consistent results. “This helped us develop a comprehensive system comprised of all the components that are now the framework of GIA’s Diamond Cut Grading System.”

Gilbertson and Green described in detail the seven components that must be considered together when assessing the overall cut quality of a diamond: brightness, fire, scintillation, weight ratio, durability, polish, and symmetry. “There will be five overall cut grades in the GIA Diamond Cut Grading System, which will initially be applied to all standard round brilliant diamonds in the GIA D-to-Z color grading scale, and from Flawless to I3,” Gilbertson said.

“It is not one proportion, but the combination of proportions that must be considered to adequately assess the overall cut appearance and quality of a diamond,” Green said. There is a wide range of appearances in each grade category, he explained, which will provide flexibility to manufacturers, retailers, and consumers.

Since diamonds in the same grade category may have different – yet equally pleasing – appearances, Gilbertson noted, the retailer can emphasize the romance of personally choosing a diamond to the customer.

To assist individuals in predicting the GIA diamond cut grade for almost any set of round brilliant diamond proportions, Gilbertson and Green said the Institute is creating a comprehensive Diamond Cut Grading Reference System. An online version of this software will be available on the GIA website, accompanied by an online tutorial of the cut system. The Institute also plans to incorporate a version of this reference system into standard optical measuring devices.

“Manufacturers will be able to use the predictive power of the reference system to plan the cutting of polished diamonds from rough,” Green added. “This will allow them to attain higher cut qualities while also maximizing their yield in the cutting process.”

GIA plans to add the new cut grade to its GIA Diamond Grading Report and Diamond Dossier® later this year. A reissue service to update recent reports, which will not require that diamonds be resubmitted, will also be available. “Details are still being determined for this,” Green said.

To support the launch of the new reports, information about the new cut grading system will be incorporated into GIA Education courses. Information will also be made available through ongoing seminars and trade show presentations, Institute publications, counter materials made available to retailers, and the trade press.

“We firmly believe that the public interest is best served by creating an unbiased and independent cut grading system that properly identifies well-made and poorly made diamonds,” said GIA Gem Laboratory CEO Thomas C. Yonelunas.

For more information on GIA’s Diamond Cut Grading System, refer to Gems & Gemology’s Fall 2004 issue. Visit GIA Research for updates.

Feb. 18, 2005