Assessing Cut

On page 100 of the September 1999 issue of JCK, in an article about the Gemological Institute of America Symposium, a statement reads, “Panelist Al Gilbertson, an appraiser from Portland, Ore., said that he and others are already using spectrophotometers for [measuring brilliance and dispersion]—so who needs computer models to determine angles and percentages?”

This is not a statement I would have ever made, nor do I know of any scientific work that supports it. I certainly think that GIA’s work is needed, contrary to the inference. While I have a slightly different view of some of the issues as they were discussed in Gems & Gemology, their contribution is invaluable to our understanding.

To be specific about the above statement, I am unaware of any spectrophotometers that have been proved scientifically to actually measure brilliance or dispersion. So far as I know, they are useful only as an indicator of dispersion at 90 degrees to the table and exact results are not repeatable, begging the question of their reliability at that solitary position. Additionally, I am unaware of any scientific evidence that spectrophotometers can measure brilliance.

Professionally, I am very interested in the topic of cut. I have been working with computer imaging that looks at some measure of light leakage and efficiency of light return. As early as 1980, I wrote to Robert Limon, head of the Diamond Standards Committee for the American Gem Society, urging that the apparently flawed mathematical treatise by Tolkowsky be revisited and analyzed by computer modeling. Some of my early concepts were incorporated into the methods used by Diamond Profile Laboratory (DPL). Our efforts in attempting to quantify light leakage were presented in the Rapaport Report several years ago. While I am no longer a consultant to DPL, this is an area of ongoing research for me. I was asked by the late Vince Manson of GIA to present some of my findings this past summer at the GIA Symposium. I felt honored to first share those results in the poster sessions and very privileged to be asked to be a panelist in the symposium “war room” on the issue of cut. It needs to be emphasized, however, that my research is not based on spectrophotometry.

I applaud your efforts to summarize the events at the symposium. The consequences of the sessions will be felt by our industry for years.

For more details on my findings, your readers can contact me directly at Gem Profiles, P.O. Box 191, Albany, OR 97321; (503) 274-2895, e-mail: al.gilbertson@cmug.com.

Al Gilbertson, Gem Profiles, Albany, Ore.

Tension Setting

When I experimented with tension setting for the first time in 1968, with an emerald solitaire, it was not in search of a new process, but more modestly as an unusual way to cover a deep mark on the table of a client’s stone. Nevertheless, tension setting it was, and it owes nothing to Niessing, Steven Kretchmer, or whoever preceded or followed them. The cast bezel molded on the stone pavilion was in 18k yellow gold, while the mounting was in hand-wrought 18k white gold. This ring has been worn for many years without the emerald falling out.

As several JCK stories through the years have touched on this subject, including the installment of “The Century Behind Us” in your September 1999 issue, the disclosure of a forerunner to modern tension setting might interest readers.

Georges Schwartz, Montreal, Quebec, Canada

JCK responds:

While we certainly try our best to research every topic carefully, we realize there are probably many individuals such as Mr. Schwartz making discoveries and doing work that precedes or parallels that of their better-known contemporaries. We thank him for bringing his own work to our attention.—The Editors

‘Wonderful Surprise’

In February, at the American Gem Trade Association show, when you asked if you could photograph one of my special pearl pieces for an upcoming issue, I was very flattered. I never imagined I would see it on the cover. What a wonderful surprise.

I have been reading JCK for about 25 years, and I know I am not alone in considering it the magazine for the jewelry industry. I am honored that you chose one of my designs for your cover. This is without a doubt one of the highlights of my career.

Stuart Artelle, Artelle Designs, Minneapolis

Corrections

Credit for the cover photograph on our October issue was inadvertently omitted. The photographer was Ned Rosen, who lives in New York City.

In “How to Choose a Colored Gem Lab” (JCK, October 1999, p. 130) the address of the International Gemmological Institute was incorrectly listed. The correct address is 579 Fifth Ave., New York, NY 10017. Jerry Ehrenwald is IGI president, not the owner.

In “Grade Expectations: How to Choose a Diamond Lab” (JCK, September 1999, p. 122), HRD personnel were incorrectly identified. Peter Meeus is general manager. Mark Van Bockstael is the manager of the HRD Institute of Gemmology. P. Grabowski is manager of the HRD Certificates Department.