sapphire, treatments.6, diffusion, bulk diffusion, surface diffusion, lattice diffusion, heat treatment, gems

In October 2001, Australian gemologist Terry Coldham informed the author of a new treatment for orange sapphire. His initial report was that a burner in Chanthaburi, Thailand had developed a new method to treat off-color Songea (Tanzania) stones to a fine orange to red-orange color. Shortly thereafter, several other sources confirmed the news. The stones were to be marketed under new names, such as Sunset sapphire, etc. AGTA Lab Director Ken Scarratt visited Bangkok last December and obtained samples. Pala International's Bill Larson also purchased samples of these stones in early December 2001 in Bangkok. When Scarratt examined his stones back in New York, he found that all had been exposed to high-temperature heat treatment. But under immersion, many displayed unusual orange color rims surrounding pink cores, suggesting there might be more to this than a simple bake job. On December 28, 2001, Scarratt asked the author if he knew anything about the stones, mentioning the orange color rims. We quickly examined the Pala stones just purchased in Bangkok and found identical color rims on most pieces. Shortly thereafter, the AGTA issued a Lab Alert and we sent a number of stones to the GIA for analysis. The following is based upon the AGTA Report of Jan. 8, 2002 and GIA reports of Jan. 28, 2002 and Feb. 16, 2002, along with discussions we have had with American experts, such as John Emmett, [1] and other dealers and gemologists around the world. [Note: new online reports by the GIA and AGTA were issued on April 19, 2002, with further updates on May 3, 2002 and 5 Sept., 2002]