Researchers from the Superabrasives division of General Electric Company (GE) recently announced a new product they have developed: strongly luminescent greenish yellow to yellow-green diamonds, or saturated yellow diamonds, that have been transformed from natural type I brown diamonds (J. Casey, pers. comm., 1999).

GE has indicated that, unlike most earlier treated-color diamonds in this hue range, the stones are not exposed to laboratory radiation; rather, GE uses high-pressure, high-temperature (HPHT) treatment. These are the same general conditions that GE researchers described in the Fall 1999 issue of Gems & Gemology (see the box titled 'Research on diamonds at the General Electric Company,' by T. Anthony and J. Casey, on page 15 of the article 'Observations on GE-processed diamonds: A photographic record,' by T. M. Moses et al.). Although the exact conditions to which these colored diamonds are exposed have not been divulged, we believe that they are roughly similar to those used to remove color from type IIa diamonds.

The figure shows the color range of this new product. These diamonds are quite similar in appearance and gemological properties to the luminescent 'green transmitters' that we observed in the fall of 1996 and reported in the Summer 1997 Lab Notes section (p. 136). We thought at that time that the treatment was probably being done in Russia with the presses that are used to grow synthetic diamonds, a suspicion that was later confirmed through conversations with a client.

Over the last several months, GIA researchers have also examined similar colored diamonds, also with strong green luminescence, that were loaned to us by Novatek Company (Provo, Utah). Novatek has recently begun to market this product under the name Novadiamond and plans a formal announcement to the trade at the February Tucson show. Novatek representatives have told us that these diamonds, too, are subjected to an HPHT process, for which a patent is pending. More recently, a New York client brought us yet another selection of similar treated-color diamonds from the Far East, reportedly treated in China.

We have had the opportunity to test samples from each group—General Electric, Novatek, and reported Chinese—and our preliminary results for 47 of these diamonds show that their properties are similar to those described in the 1997 Lab Note mentioned above. The treated diamonds fluoresce a strong greenish yellow to long-wave UV, and generally a weaker greenish yellow to short-wave UV, with some localized chalkiness to both. For all three groups, the mid-infrared spectra showed that these were type I diamonds, with moderate to high amounts of nitrogen, and typically with more B aggregates than A aggregates (see, e.g., E. Fritsch and K. Scarratt, 'Natural-color nonconductive gray-to-blue diamonds,' Gems & Gemology, Spring 1992, especially pp. 38–39). Many of these diamonds showed well-defined color zoning, with brown to yellow octahedral graining observed when examined with diffused light. Excitation with a strong light source such as a fiber-optic illuminator causes these colored graining planes to luminesce bright green; this luminescence strongly contributes to their characteristic overall face-up greenish color.

Typical features observed with a handheld spectroscope in these HPHT treated-color diamonds are a weak absorption line at 415 nm, a pair of lines at 495 nm and 503 nm (which vary in strength from stone to stone), and emission lines at about 513 and 518 nm. This spectrum is not indicative of treatment for this color range, but it implies that the diamond requires further inspection. UV-Vis-NIR spectroscopy corroborated these absorption features, and showed the H2 peak (at 985 nm) in all of the samples that had a green component to the color. Magnification revealed that, like the treated-color diamonds described in 1997, a number of the samples from each source showed evidence of high-temperature exposure, such as frosted naturals, frosted feathers, or faceted girdles with bearding.

Thomas Moses and Ilene Reinitz