corundum, treatments.6, diffusion, gems

The first reaction we had to a group of 21 quite clean" blue cabochon natural sapphires received in our New York lab was: "Something is suspicious. Why didn't the cutter facet them?" Sure enough, under immersion the color proved to be surface induced, or as we state on reports: "Natural sapphire with color synthetically enhanced by a surface diffusion process." We are definitely against saying "Natural sapphire, treated color," because it is not the same as, nor as durable as, plain heat treatment. The evidence of surface diffusion of blue natural sapphire cabochons is best seen at the girdle edge (figure 15)."