The Ideal Round Brilliant Cut
The 57-facet Standard Round Brilliant Cut (SRB) has evolved over several hundred years of diamond cutting. Its finest cut quality has historically been called Ideal. Many consider the Ideal Round Brilliant style of cut superior because its cut quality (called its ‘make’) brings out the best in diamond beauty; the best brilliance, fire and sparkle. The quality of these attributes of diamond beauty is referred to as the diamond's “optical performance” or its “light performance” (Cowing, M., 2005)
Diamonds in a range of cut proportions that are seen by diamond cutters and many other experienced observers as having greatest beauty possess the best combination of brilliance, in both its aspects of brightness and contrast, fire, and scintillation (sparkle with movement) (Cowing, M., 2005). This is the essence of the Ideal Round Brilliant.
Today, consumers in increasing numbers are looking for diamonds with the best possible beauty, i.e. the best light performance. They look to jewelry retailers for proof of perfection of cut. In turn, the jewelers often look to the diamond grading laboratories or gemologist-appraisers for assistance in providing consumers with confirmation of the quality of their diamond’s make.
The laboratories of GIA and AGS appear to be divided as to the finest or ideal make in the round brilliant diamond. The AGS believes “Tolkowsky was right” (Bates, R., 2004), and that the angles and proportions within a narrow range of the Tolkowsky Ideal have the best optical performance. The GIA has found: "There is
no one set of proportions that yields the most beautiful diamond"(Boyajian, W., 2004). Instead, there are many different proportion sets that are seen as top performers. “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” (Boyajian, W., 2004).
GIA’s grade or measure of make has five levels. The highest is ‘Excellent'. The range of angles and proportions that attain the GIA ‘Excellent’ grade is larger than that of the AGS ‘Ideal 0’ grade. Although there are significant differences, the Excellent grade is best compared to the top two grades of the 11 grade AGS system, each comprising the top approximately 20% of the grades in both systems.
Several diamond cutting houses and retailers, some grading laboratories, and some gemologists and researchers including the author set the bar for the best make higher in some respects than either GIA or AGS. In a sense you could say they answer to a higher authority. For this investigator, that authority comes from a “direct assessment” of the diamond’s optical performance in typical illumination circumstances. (Cowing, M., 2005)
Consider the Commonalities
The question is how to reconcile the differing viewpoints. The answer is found by considering aspects that these different viewpoints have in common. I find that there are more aspects of agreement among the cut grading systems than disagreement. To discover the best round brilliant diamond make,