10 ct HPHT-Treated CVD Laboratory-Grown Diamond
Recent years have seen several size milestones for faceted diamonds grown by chemical vapor deposition (CVD). In all the published reports that commented on treatment, these record-size CVD diamonds were indicated to be as-grown and with no indications of post-growth treatment (Winter 2016 Lab Notes, pp. 414–416; “IGI Hong Kong certifies largest CVD grown diamond to date,” 2020, https://www.igi.org/gemblog/igi-hong-kong-certifies-largest-cvd-grown-diamond-to-date/; Spring 2022 Lab Notes, pp. 54–56). For other recent milestone CVD diamonds reported within the trade, we could not confirm whether they were as-grown or treated. At the time of publication, the current benchmark is a 30.18 ct H-color diamond reportedly grown by Ethereal Green Diamond (Rapaport News, June 12, 2022).
Against this backdrop, a notable 10.04 ct CVD-grown diamond (figure 1) was recently submitted to the Carlsbad laboratory for a laboratory-grown diamond report. This emerald-cut stone with G color and VS2 clarity had several growth remnants, including a cloud of dark non-diamond carbon. As with all laboratory-grown diamonds, it underwent extensive testing including spectroscopy to verify its CVD origin. IR absorption spectroscopy identified it as type IIb with an uncompensated boron concentration of ~2 ppb. Spectral features such as the lack of a 468 nm peak in photoluminescence along with the coloration in the DiamondView fluorescence imaging (figure 2) confirmed it had undergone post-growth treatment (W. Wang et al., “CVD synthetic diamonds from Gemesis Corp.,” Summer 2012 G&G, pp. 80–97).
Many CVD-grown diamonds are subjected to high-pressure, high-temperature (HPHT) treatment after growth to remove a brownish appearance caused by extended defects (such as vacancy-related complexes). The brown color often correlates with a faster CVD growth rate, which the manufacturer uses knowing the color can be reduced by treatment afterward. It appears that when manufacturers create a CVD diamond of record-setting size, the growth is performed so slowly that subsequent HPHT treatment is not required for a colorless to near-colorless grade.
While some 80% of colorless to near-colorless CVD-grown diamonds have been subjected to post-growth treatment to reduce their brownish coloration (S. Eaton-Magaña et al., “Laboratory-grown diamond: A gemological laboratory perspective,” Journal of Gems & Gemmology, Vol. 23, No. 6, 2021, pp. 25–39), this treatment is not often applied to larger stones. Therefore, evidence of HPHT treatment in a CVD-grown diamond larger than 10 carats is noteworthy. These products will likely become more commonplace in the future.
