January 4, 2002
Padparadscha Treatment Surfaces
Several gem dealers as well as the American Gem Trade Association Laboratory are warning buyers about pink sapphires from Madagascar which have undergone a new form of heat treatment that alters their color into highly desirable pink/orange.
A rarely encountered balance of orange and pink hues in natural sapphires, known as padparadscha sapphires, are prized by connoisseurs and gem collectors. Their value far exceeds that of pure orange or pure pink sapphires.
Dealers say padparadscha-like sapphires have recently surfaced in gem markets in the Far East in unprecedented quantities and sizes (up to 5-6 carats), raising the possibility they've been subjected to a new treatment. "It is the hottest thing in Chanthaburi, Thailand," says Yianni Melas, a gem buyer for Swarovski Co. "Nobody can figure out how it is being done, all we know is that a lot of gems with orange to padparadscha colors are being introduced into the market."
Many dealers say the gems originate in Madagascar, where pink sapphires are available in large quantities.
The AGTA Lab's Ken Scarratt saw several of the stones on a visit to Bangkok, Thailand. He analyzed several and says initial findings point to very high temperature treatments, as well as the diffusion of an unknown element into the surface of the gem material. Some reports say that element may be oxygen. The microscopic, near-surface coloration causes the sapphires to appear orange after they emerge from heating furnaces, though the body of the gem remains pink inside. After light recutting, the orange component is reduced, and a blend of pink and orange becomes visible.
"The good news is that the treatment appears to be quite identifiable," says Scarratt. "For one, the high temperature treatment causes inclusions to have identifiable features such as glassy residues and expansion fractures that occur during high-temperature heating."
Scarratt says padparadschas with natural colors or non-diffusion heat treatments tend to show clouds of pink and orange hues inside the gem. Because of the apparent size of the market, Scarratt says suspicious stones should be sent to laboratories for proper confirmation of color origin. The AGTA Lab is investigating what process is being used to cause the surface coloration, and whether the surface coloration is stable.
by Robert Weldon, G.G.