Gubelin Gem Lab Concludes Study of GE POL Diamonds

Over the past 12 months, the Gubelin Gem Lab (GGL) operated by the Gubelin jewelry firm in Lucerne, Switzerland, has been analyzing high-pressure, high-temperature (HPHT) processed diamonds such as GE POL Bellataire. The goal of its research is to determine what gemological tests can be used to accurately distinguish processed from non-processed diamonds.

Previous studies by groups such as the Gemological Institute of America, the Swiss Gemmological Laboratory, and De Beers have claimed varying degrees of success. However, GGL was able to significantly expand its research by being the first laboratory to actually examine before-and-after GE POL processed diamonds. Because of the significance of its work, GGL had been in contact with other laboratories as its examinations progressed to offer important data on their research.

The GGL study concluded that while it is important to ascertain a diamond’s inclusions, spectra, and photoluminescence, none of these tests alone will positively identify the origin of color of an enhanced diamond. In order to determine whether the diamond has undergone HPHT treatment, the gemologist must examine all of these properties to fully understand what, if anything, has taken place.

For the research gemologists at GGL, this is not a big surprise. In fact, many gemstones are identified via process-of-elimination testing: looking at a number of key identifying features after all of the tests have been completed, before making a final determination. In fact, there are very few stones today that can be identified unequivocally by examining just one gemological property.

One of the issues the GGL examined was whether microscopic details would be helpful in identifying these processed diamonds. Other laboratories have published photos of numerous interesting inclusions. Because of the unusual nature of treatable type IIa diamonds, many of these inclusions were found by GGL to be present in untreated, non-processed stones. No changes in these inclusions were seen after the stones were processed. One inclusion, however-slightly expanded feathers-does appear to be an indicator of HPHT. But it is unwise to make an identification based solely on this observation, as not all HPHT processed diamonds have this feature.

While it would have been nice to find more microscopic visual clues, much of GGL’s background research took them to the atomic level of the diamond crystal. For instance, several theories have suggested that type IIa GE POL diamonds feature a stressed growth atomic lattice shift-caused by volcanic eruption-that is somehow corrected (“snapped back”) under HPHT. GGL has found this to be false. There is crystal distortion, but HPHT does not correct the growth.

However, within this distorted crystal structure lies an infinitesimal amount of nitrogen, which the HPHT process reconfigures with other nitrogens in the crystal lattice. This incredibly minute and complex event inside the diamond is the cause of the de-coloring of the brown type IIa diamonds, and can be seen through three different gemological tests-two using Raman spectroscopy, and the third using cathodoluminescence.

Regardless of their efficacy, these obscure and expensive techniques are certainly not within the capability of standard desktop gemological instruments. This means that the identification of HPHT diamonds can only be accomplished by well-equipped and -staffed gem testing laboratories such as GGL.

GE is not the only company using a de-coloring process on type IIa diamonds. The Russians have been successful at this enhancement, and reports from Sweden, Israel, the U.S., and Japan also tell of this capability. Obviously, then, not all HPHT processed diamonds will be inscribed “GE POL.” Therefore, the ability to identify these gems becomes ever more crucial as more de-colored diamonds are released into the trade.

The HPHT process can also create fancy colors-for example, the yellow-greens, which have been reported in JCK. However, GE has also been able to create (though very rarely) pinks and even blues. While most of the pink and blue stones are faintly colored, GGL has seen a 14-carat fancy deep pink that was created by HPHT.

The full story, including a complete description of all of the necessary tests, along with photographs and spectra of their findings, will be published in the next issue of Gems & Gemology by the GIA.

Gary Roskin