corundum, properties.3, Burma.12, Möng Hsu, gems

The article Update on Diffusion-Treated Corundum: Red and Other Colors" (S. F. McClure et al., Gems d Gemology, Spring 1993, pp. 16-28) focused on treated stones in purplish pink, reddish purple to purplish red, and orangy red hues. One feature documented in many of these sample stones, in contrast to documented blue diffusion-treated sapphires, was the presence of unusually high refractive indices. The authors speculated that this was due to the high chromium content in the diffused surface layer, and they made reference to a report in the literature mentioning high R.I. readings from high-chromium-content rubies and orange sapphires from Malawi."