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January 2000

Diamonds: Gemology

Unanswered Questions about GE/POL

GIA's first round of findings about the treated diamonds is out

The Gemological Institute of America's study of almost 900 GE/POL diamonds hints at some identifying characteristics but leaves a multitude of unanswered questions on the treatment.
Leon Tempelsman, president of Lazare Kaplan International and subsidiary POL, which distributes the diamonds, has stated publicly the studied diamonds were early samples and some gemological features GIA identified are not found in later samples because the process was subsequently improved.

Tempelsman also dashed hopes that a determination of a diamond's type could be used as an identifying characteristic of the treated diamonds. GIA said most diamonds it examined were Type IIa, but Tempelsman said General Electric, which developed the process, hopes to apply the treatment to a wide range of diamond types.

Though frustrating to gemologists, this news doesn't negate the progress GIA is making in its research. It will continue to examine later samples of treated diamonds to reveal identifying characteristics.

Several other leading laboratories, such as the Gübelin Gem Lab in Lucerne, Switzerland, are studying GE/POL diamonds also.

Diamonds in Question

The GE/POL diamonds GIA studied range from 0.18 carat to 6.66 carats. Eighty-five percent are fancy shapes, and 80% are in the D-G color range. The report's authors – James Shigley, Thomas Moses, Shane McClure, John Koivula and Mark Van Daele – expressed surprise about the high clarity of the studied diamonds. Sixty-one percent are IF or VVS1 and the rest are in the VVS2-VS range, with a small percentage of SI and I clarities. The vast majority of the diamonds GIA examined are Type IIa.

Studies at other labs confirm GE's statements that GE/POL diamonds are more than just Type IIa. Chris Smith, director of the Gübelin Gem Lab, says that in the infrared region of the spectrum, the GE/POL diamonds would be classified as Type IIa. "Upon closer inspection and expansion of the region where nitrogen impurities may be found [a defined area of the spectrum from 1000 to 1400 cm-1], very minor concentrations of nitrogen absorption typical of Type Ia diamonds have been recorded in a small percentage of the diamonds examined to date," he says.

GIA's report adds information to previously announced findings that 75% of the diamonds exhibit internal graining, creating a hazy appearance. It also says surface-reaching cleavages in the diamonds in some cases have a black area, with one black mass identified as graphite. A number of included crystals are surrounded by a roughly spherical black patch (see photo at right). Also, 80% of the gems emit no fluorescence.

Lingering Questions

Among the questions all the labs are trying to answer is exactly what high temperatures and pressures are involved in the treatment (GE has confirmed it uses high temperature and high pressure to whiten the diamonds). A high-temperature/high-pressure situation causes diamonds to occur in the first place. For this reason, experts say lab-induced HTHP may change the color and the basic structure of a diamond crystal. If the temperature and pressure leave the crystal unaltered, another mechanism or catalyst could be involved in improving the color.

Martin Haske of Adamas Gemological Laboratories, Brookline, MA, wonders whether the treatment might include a cleaning mechanism. "The hazy appearance and generally high grade of the stones would support that view," he says. Haske points to a patented process involving the removal of impurities from diamonds that involves HTHP and the use of acids or alkalis to leach out impurities. "A lot of clues might be detected in unpolished rough before they are polished away in the cutting process."

But the most important unanswered question remains: Are there any tests on the horizon to identify these diamonds if the GE/POL girdle inscription that POL agreed to place on them has been removed after the diamonds reach the market? Only time and more research will tell.

by Robert Weldon. G.G.

This GE POL diamond shows a banded strain pattern when viewed under cross-polarizers. A large number of GE/POL diamonds show strain patterns, says GIA.
A partially healed cleavage has an unusual granular appearance. GIA saw surface cleavages less frequently than internal graining.

Characteristics such as this small solid inclusion surrounded by a black patch thought to be graphite and then an outer layer of tiny outward radiating cracks were seen in some GE/POL diamonds.

Copyright © 1999 by Bond Communications.


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