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Are Ideal-cut diamonds really ideal?

One thorny issue on the four C's is CUT. While the three C's are very straight forward to understand, the evaluation of CUT is an area of no uniform agreement.

News Article

Many stores in the area promote what are called "Ideal-Cut" diamonds and charge very premium prices on them. Are they really better than other cuts? If they are, reputable diamond grading labs should be able to grade CUTs just as they do with colors and clarities. But as we are well aware, there is no standard grading on CUTs.

GIA has been doing extensive research on this subject for a number of years. The following news clipping is a statement made by the president of the GIA, Mr. William Boyajian in the fall of 1997, as appeared in the National Jewelers magazine on page 14 of the November 16th issue.

Well, it seems as though the burden rests on you to pick the most sparkling diamond rather than relying on numbers and precentages. We at FIVE STAR DIAMONDS will show as many diamonds as you would like including AGS000(AGS Triple Zero) cuts, so that you can pick the most beautiful diamond for her.

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GIA's President Bill Boyajian recent article on Cut Grading

In reference to articles and correspondence in recent issues about the dilemma of proportion grading the Towkowsky model alone, I would like to offer the following thoughts.

Bill Boyajian, President, GIA: "most diamond grading systems in use today establish parameters for cut grades in round brilliants based on a variation of proportions devised by Marcel Tolkowsky in 1919. For nearly 80 years now, there have been few, if any, rigorous attempts to shed more light on the subject...This much anticipated first article on GIA's three-dimensional, ray-tracing computer model addresses...brilliance, based on what the authors call 'weighted light return.'" "We also know that there are many combinations of proportions that yield equally bright round-brilliant-cut diamonds. In fact, we know that Diamonds can be cut in a fairly wide range of proportions to yield the same high light return, which can lead to better utilization of the rough and a better fit with the myriad tastes that exist in the global marketplace." "Finally, we know from our extensive historical research on cut that there have been numerous claims to a single set of 'Ideal' proportions in round-brilliant-cut diamonds...The derivation and use of the term "Ideal" is thus confusing at best...Although it is not GIA's role to discredit the concept of an 'Ideal' cut, on the basis of our research to date we cannot recommend its use in modern times." Conclusions about cut can not and must not be drawn from individual measurements any more than the outcome of a football game can be drawn from any one play. Moreover, GIA's three dimensional computer ray tracing research to date indicates a multiplicity of proportion options yielding significantly beautiful stones - certainly no less beautiful than a Towkowsky proportioned round brilliant- that in many cases are more attractive to many eyes. One example discovered in our investigation of modeling proportions of a round brilliant cut diamond revealed that, by our method of calculating brilliance, a 59 percent table is more brilliant than a 53 percent table, which was defined by Towkowsky as "ideal" This calculation was based on maintaining all other angles defined by Towkowsky. Perhaps more important, it appears that brilliancy alone can also be affected by the interrelationship between different sets of angles from the crown and the pavilion. Even if the diamond the smaller table happens to show more fire, we question the sensibility of dictating to consumers that a diamond with a larger appearance and more brilliance is worth less than one with more fire. The results of our preliminary research are currently in preparation for publishing in our quarterly journal, Gems and Gemology.

This leads to a second thought regarding the reporting of cut on diamond grading reports and the use of optically sophisticated equipment in that process. It is a further trap for the trade to adopt measurement parameters that are altogether too strict in their reporting. Anyone can print out a host of dimensions from todays noncontact optical measuring devices and appear to be doing the public a great service. While anyone rushes to be the first to carve a niche in the marketplace for diamond grading and cut analysis, we caution trades people to avoid embracing unproven standards that may create a public backlash rather than a diamond boon.

It took decades of extensive research using high technology to bring the industry to a more modern and scientific understanding of proportion considerations in a round brilliant cut diamond. While I doubt that it will take as long to further our knowledge of cut, I fear that the premature use of information without a thorough understanding of its scientific basis and practical implications is a bubble waiting to burst.
WILLIAM E. BOYAJIAN
PRESIDENT
GEMOLOGICAL INSTITUE OF AMERICA


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