When Richard T. Liddicoat created the now de facto international diamond grading system in the early 1950s, he was able to establish standards and nomenclature for color and clarity that would eventually become part of our everyday diamond lexicon. He was less confident in his ability to create a standardized system for cut that could adequately deal with both the scientific aspects and the multitude of tastes in the marketplace. Liddicoat therefore developed a system of “corrected weight” from which students could arrive at reasonably accurate diamond cut quality (and even pricing) determinations based on proportion deductions from the so-called American Ideal round brilliant. This system provided the basis for GIA’s diamond training in cut for some three decades. However, when diamond prices skyrocketed in the late 1970s and subsequently crashed in the early ‘80s, the corrected weight system became less relevant.

GIA formally revised its diamond courses to reflect this change in the mid-1980s. For years afterward, some in the trade were still questioning our shift away from corrected weight toward a more generalized training system that did not hold the American Ideal cut as a standard to which all other round brilliants were compared. And yet another debate emerged: Some people wanted a cut grade, while others were vehemently against it. We knew, however, that fundamental to the concerns of this debate was the question of whether cut could be objectively assessed, and whether that assessment could be made scientifically, using modern resources.

Our commitment to contemporary research on cut reached a new level in the late 1980s, when computer technology had advanced to the point where we could analyze features of diamond appearance that heretofore had not been feasible to explore. As a result, in 1988 we made the critical decision to fund a substantial grant to a young mathematician then in graduate school at the California Institute of Technology (Caltech) in Pasadena. We had no idea at the time that a project to develop a highly technical three-dimensional computer model of a “virtual” diamond using sophisticated ray-tracing software would evolve into a 15-year, multi-million-dollar study of every aspect of cut appearance in round brilliant diamonds. What began as pure research has now resulted in a scientifically based, but eminently practical, grading system for categorizing cut in standard round brilliants.

The feature article in this issue, authored by Tom Moses and a host of GIA professionals, is the third in a series of landmark articles on cut in round brilliants that we are proud to bring you in Gems & Gemology. The first, published in 1998, was from a group led by that “young mathematician” from Caltech, Scott Hemphill, and focused on what we called “weighted light return,” a metric for reporting brilliance (which we have since determined is best described as brightness). The second article, published by Dr. Ilene Reinitz and co-authors in 2001, focused on dispersed colored light return, a metric for fire. These two articles formed the basis of our assessment of cut in round brilliants, but brightness and fire alone were not enough.

A third component, scintillation, needed to be examined before we could fully understand the factors that contribute to diamond cut appearance. Our researchers turned to observation testing with experienced people from different trade segments, as well as consumers, to explore this element. They found that although some aspects of scintillation (those related to sparkle) were included in the brightness and fire metrics, there was also an important underlying element that affected the appearance of scintillation itself. This element, called “pattern,” represents the size and arrangement of bright and dark areas in a diamond, and is a key component of the extent to which observers find a diamond attractive. We found from our interaction with the trade that this phenomenon was considered part of the “life” of a diamond—a common term used to describe desirable stones.

Observation testing and interaction with the trade also established the importance of other aspects beyond cut appearance—design and craftsmanship—in the assessment of a diamond’s overall cut quality. These include durability and “over-weight” concerns, as well as polish and symmetry. In addition, we used observation testing to fine-tune our original brightness and fire metrics, so they would more accurately reflect real-world conditions. The current article discusses all these elements of cut and describes how we validated the very sophisticated model we created.

Our authors aren’t the first to use computer modeling to predict the effects of various proportion sets on the cut appearance of diamonds. To our knowledge, though, no other organization or research group has validated their models to the extent GIA has with observation testing of actual diamonds by experts in the field, a major part of the research described in the present article.

While GIA has studied cut in diamonds for decades, our concentrated effort—particularly over the past 10 years—has now yielded breakthrough research that will undoubtedly alter historical practices and traditional perceptions of many in the diamond industry. The main conclusions are as follows:

• Individual proportions must not be assessed on their own. It is the complex interrelationship of individual proportions that matters most in the face-up cut appearance and overall cut quality of a diamond.
• There is no one set of proportions that yields the most beautiful diamond. Similarly, the long-held view that expanding deviations from a fixed, arbitrary set of proportion values produces diamonds with increasingly poorer appearances is simply not valid.
• Truly consistent and accurate comparisons of cut in diamond require a standardized viewing and lighting environment that is representative of common environments used in the trade.
• Whereas other systems for assessing cut in round brilliants have from three to 11 different classification categories, our research found that most individuals could consistently discern five levels of different cut quality.
• For a grading system to be truly unbiased and objective, it must allow for personal and global preferences in diamond appearance.

Once we determined that a comprehensive system for assessing diamond cut in round brilliants could be developed, we were still left with the fundamental question of whether a diamond cut grade was useful for the public and the trade. Although there actually has been a tremendous amount of industry interest in the creation of an objective, scientifically based system for assessing diamond cut, ultimately the decisions on this project and the directions GIA has chosen were derived from its mission—to ensure the public trust in gems and jewelry by upholding the highest standards of integrity, academics, science, and professionalism through education, research, laboratory services, and instrument development. GIA firmly believes that the public interest is best served by creating such a system, and that its impact on the trade will also be positive.

As such, the authors and their colleagues have used this extensive research to develop a cut grading system for round brilliants that will be incorporated into GIA’s diamond training in education and into diamond grading in the laboratory in mid-2005. For years, many in the trade have maintained that a wider set of proportions could yield an equally beautiful diamond; to some extent, these people are vindicated by the results of our research. Diamond manufacturers will be able to cut round brilliants to a wider range than the current norm and still achieve top-grade, great-looking diamonds. An even wider range of proportions can produce pleasing diamonds in the upper-middle to middle grade ranges. Each of these grades will, in many cases, allow for greater yield and weight retention from the rough.

Ultimately, the new GIA diamond cut grading system will provide answers to the long-debated questions about the fourth C in diamond grading. As a result, dealers and retailers will have definitive categories for cut in round brilliants and thus will be able to better serve their clients. And consumers will have access to information that was heretofore either nonexistent or unavailable as an international standard. GIA will soon propose that global standard.

Over the years, our research objectives evolved and expanded from first seeking a better understanding of cut, to establishing a system that would “flag” poorly cut diamonds, to building one that would also give credit to well-made stones. I am pleased to say that our objectives have been met with the creation of a truly unbiased scientific system to assess the cut grade of standard round brilliants; furthermore, the system has been validated by expert observers. We believe that this system will stand the test of time, like the color and clarity scales we created more than 50 years ago. While the process has been evolutionary, the end result may in fact be revolutionary. Only the future will tell. Research will certainly continue, and it may never stop. Cut is humankind’s unique way of adding value to that finely crystallized carbon we have all come to know and love as the king of gems.

William E. Boyajian
President, Gemological Institute of America