We publish courtesy of GIA’s Gems & Gemology G&G eBrief
Author: Paul Johnson, GIA Laboratory, New York
This 0.20 ct Fancy Intense purplish pink round brilliant proved to be a treated synthetic diamond. Photo by Jian Xin (Jae) Liao.
Many pink-to-red diamonds in the jewelry market owe their color to the natural material being treated with multiple processes, such as high-pressure, high-temperature (HPHT) annealing combined with irradiation and annealing at relatively low temperatures. This technique has also been applied to HPHT-grown synthetic diamonds since the 1990s, and today it appears that some of these synthetics are intentionally produced with very low nitrogen concentrations for a more intense color appearance after post-growth treatment.
A 0.20 ct round brilliant submitted to the New York laboratory was Fancy Intense purplish pink and contained few inclusions. Our initial observations suggested it might be one of the multiple-treated natural diamonds described above. It displayed strong color zoning and fluoresced strong orangy red to both long- and short-wave UV radiation. Absorption spectroscopy showed it was type Ia with very low nitrogen; the pink color was produced by strong NV centers with zero-phonon-line absorptions at 575 and 637 nm. These centers can be produced by multiple treatments, and an additional strong peak at 595 nm was indicative of artificial irradiation. These features are very similar to those seen in multiple-treated natural diamonds.
Careful examination with the DTC DiamondView instrument, however, revealed a subtle multi-sectoral growth structure that proved it was an HPHT-grown synthetic diamond. It appears that this synthetic diamond was carefully grown with a very low concentration of nitrogen (approximately 1 ppma), but enough to induce the high concentration of NV centers responsible for the intense pink color during post-growth treatment.
Care is needed to separate these treated synthetic pink-to-red diamonds from treated natural diamonds.