Professional Jeweler Archive: Swiss Lab Offers GE/POL Identification Service

August 2000

Diamonds/Gemology


Swiss Lab Offers GE/POL Identification Service

Following are excerpts of a poster published by SSEF Swiss Gemmological Institute and reprinted here with permission


The SSEF Swiss Gemmological Institute announced in March it found key features for the identification of GE/POL diamonds, which undergo a high-pressure/high-temperature treatment to improve their color grade.

Since then the lab has routinely performed identification of HPHT-treated Type IIa diamonds. In fact, all stones submitted for quality grading are checked for possible HPHT treatment.

Abstract

GE/POL diamonds are identified in a two-step process:

  • Because almost all GE/POL diamonds were found to be Type IIa near-colorless, these diamonds are separated from others of similar color using the SSEF IIa Diamond Spotter™ in connection with a short-wave UV light unit (254 nanometers). This result can be checked by FTIR spectrometer (Chalain et al., 1999).
  • A Raman spectrum of these IIa diamonds is obtained using the 514.5nm laser emission of a Raman spectrometer combined with cryogenic sample cooling, which cools a sample to about -180°C. This provides an excellent signal/noise ratio. A luminescence pattern at 3,737cm-1 and 2,043cm-1 proves the presence of a small number of nitrogen vacancy centers (an N-V center comprises a single nitrogen atom linked to a carbon vacancy) in the diamonds. These peaks are related to 637nm and 575nm peaks in the visible infrared spectrum. This is characteristic of the material used for the GE process – all studied GE/POL diamonds exhibit these emissions.

Most but not all non-treated colorless Type IIa diamonds show an N-V- (637nm) and N-V0 (575nm) feature. The peak height ratio 637/575 is considered indicative for treatment identification (Fisher & Spits, 2000). We found that diamonds with high ratios (>2.8) are HPHT-treated, whereas those with low ratios (<1.6) are non-treated. Further spectroscopic observations as well as possible gemological features reinforce the SSEF identification routine, which can provide identification criteria for GE/POL diamonds not showing N-V features.

Background

Beginning in March 1999, the diamond trade was in a difficult situation with the introduction of a relatively small number of near-colorless to colorless diamonds treated through a high-tech process. This HPHT treatment transforms brownish Type IIa diamonds into colorless ones of a higher value. The product was initially named GE/POL processed diamonds and is now called Bellataire diamonds. According to General Electric, which performs the quality improvement, and distributor Pegasus Overseas Ltd., the treatment is undetectable, will remain so and is permanent. The stones are graded by Gemological Institute of America, which notes the treatment on its certificates and refers to a “GE/POL” inscription on the girdle of each of the cut diamonds.

Because this laser inscription is shallow and apparently can be removed with no loss of weight, the disclosure of treatment is not safely linked to the stone. It is interesting to note the reported prices of GE/POL-treated diamonds were essentially the same as for untreated stones of comparable quality.

The problem of identification of treated gemstones is not new, but the identification of GE/POL diamonds was a serious challenge to gemological laboratories. The first articles published regarding identification concentrated on inclusions (Johnson et al., 1999; Moses et al., 1999). Spectral features were found to provide identification features that don’t require the presence of laser inscription or inclusions. (Yuan, 1999; Chalain et al., 1999 and 2000 a, b).

Chronology of Our Research

In December 1999, SSEF Swiss Gemmological Institute published the first results of its research on GE/POL-treated diamonds. Although based on only two diamonds, essential characteristics and a distinct methodology of research were shown in the Revue de Gemmologie No. 138/139. Two more manuscripts with SSEF research results were published in the Journal of Gemmology and the Zeitschrift der Deutschen Gemmologischen Gesellschaft. The information in the papers that appeared so far have been taken from room temperature spectra.

At SSEF, the advancements that enabled the detection breakthrough were based on the development of a cryogenic sample stage and recording spectra at liquid nitrogen conditions. The careful comparison of different kinds of Type IIa diamonds led to the detection of the correlations between the observed spectroscopic features.

The GE/POL research project at SSEF was done in cooperation with the University of Nantes in Nantes, France, and the University of Basel in Basel, Switzerland. The results and analytical procedure were discussed with De Beers’ DTC Research Centre; De Beers’ results were published in the Spring 2000 issue of Gems & Gemology, GIA’s quarterly journal.

Conclusions

Despite claims the GE/POL treatment was not detectable, a small group of people from SSEF and the universities in Nantes and Basel found an identification method within one year of intense research. At the same time, scientists at De Beers research center presented their method for identification.

Both groups base their identification on N-V centers, a feature not yet fully described in near-colorless Type IIa diamonds (though Chalain et al. referred to it in a 1999 report). A careful evaluation of luminescence spectra produced with a Raman laser system at low temperature allows a gem lab equipped accordingly to identify HPHT-treated Type IIa diamonds [such as GE/POL diamonds]. Further spectral features and possible characteristic inclusions may confirm the conclusion.

References

Chalain, J-P.; Fritsch, E.; Hänni, H.A.; 1999. “Detection of GE/POL Diamonds: A First Stage,” Revue de Gemmologie A.F.G., No. 138/139, pp. 30-33.

Chalain, J-P.; Fritsch, E.; Hänni, H.A.; 2000a. “Identification of GE/POL Diamonds: A Second Step,” Journal of Gemmology, 27, 2, pp. 73-78.

Chalain, J-P.; Fritsch, E.; Hänni, H.A.; 2000b. “Zur Bestimmung von GE/POL Diamanten: Erste Erkenntnisse.” Zeitschrift der Deutschen Gemmologischen Gesellschaft, 49, 1, p. 19-30, April 2000.

Collins, A.T.; 1992. “Color Centres in Diamonds,” Journal of Gemmology, Vol. 18, No. 1, pp. 37-75.

Collins, A.T.; 1999. “Things We Still Don’t Know About Optical Centres in Diamond,” Diamond and Related Materials, Vol. 8, pp. 1, 455-1, 462.

Fisher, D.; Spits, R.A.; 2000. “Spectroscopic Evidence of GE/POL HPHT-Treated Natural IIa Diamonds,” Gems & Gemology, Spring 2000, pp. 42-49.

Fritsch E.; 1998. “The Nature of Diamonds,” G.E. Harlow, editor. Cambridge University Press & American Museum of Natural History, Cambridge, U.K., pp. 38-40.

Johnson, M.L.; Koivula, J.I.; McClure, S.F.; DeGhionno, D.; 1999. “Review of GE-Processed Diamonds,” Gems and Gemology, Vol. 35, No. 2, pp. 144-145.

Moses, T.M.; Shigley, J.E.; McClure, S.F.; Koivula, J.I.; Van Daele, M.; 1999. “Observations on GE-Processed Diamonds: A Photographic Record,” Gems and Gemology, Vol. 35, No. 3, pp. 14-22.

Rapaport Diamond Report, 1999. http://www.diamonds.com. Consulted from March 1999 to January 1999.

Ringwood, George; 2000. Personal communication.

Robertson, R.; Fox, J.J.; Martin, A.E.; 1934. Philosophical Transactions, Vol. A232, London, pp. 463-535.

Schmetzer, K.; 1999. “Behandlung Natürlicher Diamanten zur Reduzierung der Gelb-oder Braunsättigung,” Goldschmiede Zeitung, Vol. 97, No. 5, pp. 47-48.

Woods, G.S.; Collins, A.T.; 1983. “Infrared Absorption Spectra of Hydrogen Complexes in Type I Diamonds,” Journal of Physics and Chemistry of Solids, Solid State Communications, Vol. 45, pp. 471-475.

Yuan, J.C.C.; 1999. “Diamond Researching. Solstar International Inc. Internal Report,” New York, NY.

– by Jean-Pierre Chalain and Henry A. Hänni of the SSEF Swiss Gemological Institute and Emmanuel Fritsch of the University of Nantes

SSEF developed the UV Transparency Spotter™ to help identify Type IIa diamonds.
Non-treated Type IIa brownish diamonds register a low response at the 637nm line using a Raman spectrometer.
GE/POL treated diamonds exhibit a more dramatic 637nm line.
These two Raman spectra of the same diamond show the dramatic differences between analysis at room temperature (lower line) and after cooling with liquid nitrogen (upper line). Note the differences in the 637nm lines.

Seen here is a camera (top) attached to a microscope and Raman spectrometer. The microscope is aimed at GE/POL diamonds immersed in a super-cooled vial of liquid nitrogen to obtain an excellent signal/noise ratio.

All illustrations are courtesy of SSEF, Basel, Switzerland


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