Lab Notes Gems & Gemology, Fall 2013, Vol. 49, No. 3

Large Pinkish Brown CVD Synthetic Diamond

IMG-FA13-LN 154344 636x358
Figure 1. This 1.03 ct CVD synthetic is notable for its size and Faint pinkish brown color. Photo by Robison McMurtry.
Distinguishing diamonds of natural and synthetic origin is one of the most important tasks of any gemological laboratory. With the advances in technology and methodology available to manufacturers, a wider variety of synthetic diamonds has begun to emerge. Recently, a client submitted a 1.03 ct emerald-cut synthetic diamond (figure 1) to the Carlsbad laboratory. We determined it had been grown from the chemical vapor deposition (CVD) process. This was evident from the large silicon-vacancy peak at 737 nm seen in both the UV-visible and photoluminescence spectra of this type IIa synthetic diamond. A lack of tatami strain and the distinctive growth patterns observed in the DiamondView (see W. Wang et al., “Latest-generation CVD-grown synthetic diamonds from Apollo Diamond Inc.” Winter 2007 G&G, pp. 294–312) confirmed the origin (figures 2 and 3).

IMG-FA13-LN 154342 636x358
Figure 2. Viewed under crossed polarizers, this synthetic diamond shows mottled strain, but no tatami strain, consistent with its CVD growth origin. Photo by Troy Ardon.
IMG-FA13-LN 154340 636x358
Figure 3. DiamondView imaging remains one of the most reliable methods for confirming a CVD synthetic diamond. This image shows distinctive growth patterns. Image by Sally Eaton-Magaña.
As the vast majority of CVD synthetic diamonds submitted to the lab weigh less than one carat, this sample was unusual for its size, as well as its color grade of Faint pinkish brown. This is the first colored CVD synthetic diamond examined by GIA that did not merit a “Fancy” modifier, but instead fell in the Faint to Light range. While pink CVD-grown synthetics have been documented, in most cases the color was generated by post-growth treatment. Here the pinkish color seemed solely related to the growth process, with no subsequent treatments (HPHT annealing, irradiation, and then annealing) coming into play.

Troy Ardon is a staff gemologist and diamond color origin specialist, and Sally Eaton-Magaña is a research scientist, at GIA’s laboratory in Carlsbad, California.