The original article from Volume 23, Number 1, January – March 2007 is not reprinted here, but a similar article was posted here on this websites on-line Journal.

Here is the GIA's letter to the Editor:

Dear editors,

The recent work by Sivovolenko et al. ("Diamond cut grading: Unintended consequences and solutions," First Quarter 2006, pp. 447-454) mentions our work on Cut Quality grading in round-brilliant-cut diamonds (RBCs). We found several inaccuracies in this article related to our research and cut grading system, and therefore felt we should take this opportunity to clarify some points for the record.

We agree with Sivovolenko et al. that the current GIA and AGSRBC grading criteria give different relative results for some sets of proportions, but we disagree with the reasons they give for these differences. What is not adequately mentioned by the authors is that there is much overlap in the cut grades from the two systems, and that many of the remaining differences in grades may result merely from the fact that our system uses five grades, while the AGS system uses eleven grades. We note that the diamond appearances in their figures 3(3) and 3(6) are brighter, not darker, than the same diamond resting on a gray background in figure 3(2); this would indicate to us a result counter to the one provided by the authors. We disagree with the authors' contention that the environment used in our research led to the favoring of "steep/deep" diamonds over those with "shallower" proportions. When diamonds stray too far in proportion space to either of these areas they are deducted for in our cut grading system. We also believe, but cannot confirm without further information from the authors, that the areas being contested are areas at the borders of our cut grade categories, and would contend that areas at grade borders are often contested in any evaluation system.

Three points in the section titled "Some Perceived Problems" warrant comment. First, as stated in reference iv (again, the Fall 2004 issue of Gems & Gemology), we knew the system needed more than just brightness and fire metrics because those two factors alone gave an agreement rate of only 58% ; in contrast, the finished GIA cut grading system for RBCs showed 92% agreement between human observations of overall appearance and system assignment of grades – the same agreement rate the observers showed with each other. We would also like to emphasize that much of our observation testing was devoted to "overall appearance" and not just to brightness and fire as stated.

Second, the Cut Group may feel that 38 million proportion combinations is "excessive and un-workable for rough planning," but both Sarin and OGI have incorporated the GIA cut grading system with this number of data points, and diamond manufacturers have been using these tools successfully for eight months.

Third, the authors' point about the difficulty of using the same approach for fancy shapes as we used for rounds is a valid one. We will need to examine the feasibility of using our cut system for RBCs as we enter our next stage of research on fancy shapes. However, we also believe that an accurate and comprehensive system for grading the cut quality of round brilliants should not be jettisoned merely because its wholesale application to fancy shapes is uncertain. Future research (including many more observation tests) will show whether our current system is applicable to fancy shapes, or whether particular shapes might need their own adapted cut grading system.

In contrast to the statement that GIA or AGS "have yet to find an adequate metric for scintillation," footnote 3 on page 454 of the article shows that the lack of a specific scintillation (sparkle) metric was based on the comments we gathered during human observations when we asked why one diamond had a superior overall appearance to another. People spoke a great deal about "dark-zone distribution" but very little about relative sparkliness. Also note in this same footnote we state that during our research we found that a diamond's relative sparkle was accounted for in our brightness and fire metrics.

The authors state that "green spectral flashes are rarely seen in a diamond," and assert that a very small aperture and a small light source at a great distance are required to photograph such a flash. As described in reference xi (Fall 2001 issue of Gems & Gemology), although our model conditions use a point light source and a hemispheric detector, both infinitely far from the virtual diamond, our photographs of fire used real diamonds, an actual hemisphere 40.6 cm (16 inches) in diameter, a hole for the light 0.95 mm in diameter with a fiber-optic light 20 cm (17.5 inches) behind the hole, a 50 mm lens and f/# of 16, yielding a camera aperture of 2.8mm, which is not "very small". This reference also showed the similarity between our modeled results and photographs despite the differences in conditions. Both photographs and human observations of hundreds of round brilliant diamonds revealed a variety of expressions of fire. Most samples displayed all spectral colors, including green. We agree completely with the authors' recommendation that readers try to reproduce this for themselves: take a round brilliant, rock it back and forth under spot-like illumination and look at the fire. See whether any of the flashes are green – our experience indicates that some will be.

There are also incorrect statements and implied assertions that do not address our work directly. For example, the earliest diamond reports containing proportions were Diamond Certificates issued by the AGS starting in 1936, and the earliest effort to grade cut from proportions was made by GIA in 1938, not in the mid 1950s as stated by the authors. Also, to the best of our knowledge, ASET (both program and viewing device) was developed by AGS and Dr. Jose Sasian; the article implies that GH was involved in its development.

In addition, we noticed technical mistakes in this article, such as almost identical captions for figures 5 and 6, and a nonsensical illustration for figure 8 with a caption that appears to belong to figure 6.

We wish Sivovolenko et al. all the best in their research intentions, but hope that any resulting articles are vetted conscientiously.

Sincerely,

The GIA Diamond Cut Group*

* The GIA Diamond Cut Group consists of:
Troy Blodgett
Ronald H. Geurts
Al M. Gilbertson
Barak Green
T. Scott Hemphill
John M. King
Mary L. Johnson
Thomas M. Moses
Ilene M. Reinitz
James E. Shigley