Pink Synthetic Displays Rare Treatment

RAPAPORT... A pink diamond recently submitted to the Central GemLaboratory (CGL) in Tokyo was found to be a chemical vapor deposition (CVD)synthetic stone, treated only with Low Pressure-High Temperature (LPHT). The marquise brilliant-cut, 0.192-carat diamond is an unusualfind, as stones of this nature are generally treated with a multistep process thatfirst uses High Pressure-High Temperature (HPHT) treatment to remove its brownhue. This is followed by electron irradiation, which modifies the stone'sstructure and physical properties. Finally, the diamond is treated tolow-temperature annealing - heating the stone to a specific temperature, and thencooling it at a very slow and controlled rate. "Pink CVD synthetic diamonds treated only with low pressureand high temperature (LPHT), without additional post-growth irradiation,have...been reported, but are rarely seen on the market," researchers HiroshiKitawaki, Kentaro Emori, Mio Hisanaga, Masahiro Yamamoto and Makoto Okano saidin the Fall 2018 issue of Gems & Gemology. Visually, the diamond was undistinguishable from a naturaldiamond. Further testing revealed the stone to be CVD, as certain aspects indicatedit had not been treated with the normal, multistep process, but instead withLPHT. While sole use of LPHT is uncommon, it may become morewidespread as the technique is improved, CGL noted. Image: The LPHT-treated pink synthetic. (Hiroshi Kitawaki/Gems & Gemology)