corundum, treatments.6, diffusion-treated, gems

The Summer 1990 issue of Gems & Gemology carried a comprehensive article on diffusion-treated sapphires. Among the materials examined were stones marketed by the firm Gem Source of Las Vegas, Nevada, and Bangkok, Thailand. At that time, Jeffery Bergman of Gem Source stated that he used Sri Lankan sapphires as starting material. Recently, Mr. Bergman shared information relating to experimental diffusion treatment of sapphires from another locality: Montana. He also donated eight of these stones, ranging from 0.53 to 1.18 ct, to GIA for study. According to Mr. Bergman, approximately 50% of the Montana sapphires they have diffusion treated to produce a blue color have also developed unwanted yellowish orange zones. Examination of the eight sample stones with magnification readily revealed the yellowish orange zones described by Mr. Bergman; also noted in some of the stones were disk-like areas of dark blue surrounding dark crystalline inclusions (figure 12). We believe that the yellowish orange areas are related to zoned growth and reflect a higher iron impurity content, while the disk-like dark blue areas are caused by internal diffusion—a cannibalization of both iron and titanium from possibly iron-rich rutile and/or ilmenite inclusions. Both of these unanticipated color areas no doubt result from the high temperatures used in the diffusion-treatment process.