GIA conducts largest-ever observation tests on the appearance of diamonds

Using a groundbreaking approach to the evaluation of diamond appearance, research scientists at the Gemological Institute of America (GIA) have studied how human observers describe and judge diamonds of various proportions under a variety of conditions. Diamond dealers, retailers, consumers, and trained observers have all taken part in this ongoing series of observation tests of diamond appearance.

Over the past eighteen months, GIA has collected nearly 40,000 observations of more than 1,000 diamonds in a variety of controlled environments as well as in typical trade settings. No cut-evaluation methodology currently used in the trade has been empirically tested in this manner.

“We work on the premise that computer modeling must always be validated by real-world observations,” said Thomas C. Yonelunas, CEO of the GIA Gem Trade Laboratory. “We are pleased to confirm that the observations gathered in this phase of our study strongly support computer-modeled results for brilliance and fire.”

Initial observation tests allowed researchers to further define relevant environmental and observational parameters, leading to refined metrics for brilliance (brightness) and fire. These new calculated predictions of brilliance and fire were then verified by “real world” brilliance and fire differences seen in diamonds. Recently, GIA conducted observation tests to determine how the two appearance aspects of brilliance and fire contribute to overall appearance.

Among those who participated in the tests were diamond dealers in both New York and Antwerp. They observed the test diamonds both in their own offices, where they make similar judgments every day, and in controlled viewing environments at GIA offices.

Trade members were given the opportunity to learn the diamonds’ proportions after their observation tests were completed. Some participants indicated their surprise at the performance of a number of diamonds specially cut to proportions considered outside standard cutting parameters. This further supported GIA’s contention that “every facet matters.” GIA has found that variations in the lengths of star and lower-girdle facets greatly impact the visual appearance of a diamond. Thus, estimates of appearance cannot rely only on pavilion angle, crown angle, table size, and total depth.

Retailers and consumers were also tested in various controlled and natural environments at other times throughout this phase of the research. In addition, thousands of observation tests have been conducted at GIA in controlled environments using experienced laboratory observers.

Research scientists at GIA are currently examining other possible appearance aspects, such as scintillation, to understand how they also might interact with brilliance and fire to determine overall appearance.

The goal of GIA’s long-term research project is to provide a scientific basis for evaluating cut in diamonds. Not only will this help members of the trade reach a consensus on a cut system, but ultimately it will also provide consumers with a higher level of confidence and comfort in their diamond purchases.

GIA plans to incorporate the findings from these observation tests into expanded cut quality information on GIA Diamond Grading Reports.

For more on GIA’s cut research project, visit the GIA Web site at

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