Professional Jeweler Archive: Labs Identify GE/POL Traits

June 2000

Diamonds/News


Labs Identify GE/POL Traits

Two studies reveal a way to differentiate GE/POL-treated diamonds and their untreated counterparts


De Beers scientists in England and South Africa have discovered a quantifiable way to identify GE/POL diamonds using spectroscopic techniques to find nitrogen vacancy centers in treated diamonds. The research was published this week in the Spring 2000 issue of Gems & Gemology, the Gemological Institute of America’s quarterly journal.

Separately, the SSEF Gemmological Laboratory in Basel, Switzerland, announced a new service to identify diamonds that have undergone the high pressure/high temperature GE/POL treatment based on its own study, which also depends on the identification of nitrogen vacancy centers.

De Beers Study

De Beers scientists examined 39 treated and 30 non-treated Type IIa diamonds. Using spectroscopic observation, the scientists studied luminescence peaks using laser excitation of cryogenically cooled diamonds. (Cooling, usually with liquid nitrogen, helps define absorption patterns).

Specifically, they recorded peaks at 575 and 637 nanometers in most of the GE/POL diamonds studied. The peaks result from nitrogen vacancy centers, which are a single nitrogen atom in a vacancy. Normally, Type IIa diamonds have little or no nitrogen; the presence of nitrogen in the GE/POL diamonds is what makes them treatable.

De Beers is working with several labs to develop a way to apply this research. Raman spectrometers in combination with cooled diamonds and laser excitation could record the differences and determine treatment. GIA says a majority of GE/POL diamonds will be identifiable when their spectral features are combined with the characteristics observed by microscope in an earlier study (Fall 1999 Gems & Gemology).

SSEF Study

The SSEF Web site says its identification is “essentially based on laser-induced fluorescence spectroscopy performed on a Raman system at liquid nitrogen temperature.” SSEF says it observed a luminescence pattern that proves the presence of a small number of nitrogen vacancy centers in all the GE/POL-treated diamonds it studied. None of the non-treated diamonds SSEF studied showed the nitrogen vacancy centers.

On a practical level, retailers won’t be identifying GE/POL diamonds using these kinds of tests because the equipment needed is prohibitively expensive. The tests will have to be done at gem labs that have the sophisticated equipment.

For copies of the Spring 2000 G&G contact GIA at (800) 421-7250, ext. 7142, dortiz@gia.edu, www.gia.edu/gandg/index.cfm. For information on SSEF’s study, go to www.ssef.ch.

Background

Pegasus Overseas Ltd., a subsidiary of Lazare Kaplan International, New York City, announced in March 1999 it would sell diamonds processed to improve their color grade. Spokesmen said gemologists would never be able to identify the treated diamonds, developed by General Electric. When the industry said the inability to detect a lab-improved diamond would undermine the market, GE and POL agreed to laser-inscribe “GE/POL” on the girdle, and POL said it would sell them with GIA certificates.

GE’s reaction to the latest news? “The study and tests are encouraging,” says Dr. Thomas Anthony, the GE staff physicist who developed the GE/POL treatment. “The test is reliable for the lower colors of diamonds – J-Z stones – because they contain nitrogen. But it’s not reliable for higher colors or clean diamonds.” [Note: For diamonds without nitrogen, examination of inclusions and how they react under HPHT may be needed. In this case, a D-flawless GE/POL diamond would not be as easily detected.] “In terms of dollar value, on a piece-by-piece basis, 90% of the stones are still undetectable,” says Anthony.

He says GE researchers are studying detection methods also, but that a 100% solution has eluded them so far.

– by Robert Weldon, G.G.

Two gemological laboratories have uncovered evidence that will help identify GE/POL diamonds, like this 1.16-ct. example from Pegasus Overseas Ltd., New York City.

Copyright © 2001 by Bond Communications