During Wednesday’s “AGTA Gemological Testing Center Update” seminar, speaker Ken Scarratt made a startling announcement concerning the new heat-treated sapphires coming out of Thailand. AGTA’s Gem Testing Center (GTC) will be identifying these heat-treated sapphires as “natural corundum, variety: sapphire, with indications of heating, surface-related color created by bulk diffusion; areas of synthetic overgrowth are present.
“They take this material and `warm it’ to 1,000 degrees centigrade,” said Scarratt. “Then they heat-treat it,” along with crushed chrysoberyl-for its beryllium content and possibly other natural elements-taking the temperature up to 1,800 degrees, for 20 hours, and then repeat the process as many as 15 times. During this entire treatment, elements from the chrysoberyl are diffused into the sapphire, sometimes changing the color on the surface, sometimes changing the color throughout, and sometimes not changing the color at all. Moreover, the surface of the sapphire actually melts, then recrystallizes. Technically, that’s a synthetic overgrowth.
Scarratt said the GTC is ready to put the new wording on its gem identification reports. “It is what it is,” said Scarratt.
On gems where the color is diffused throughout, Scarratt said GTC is still working on the identification of those stones. For the most part, these sapphires can be easily confused with the more traditional heat-treated stones, and even some completely natural unenhanced sapphires.
The new heat treatments pertain mostly to colors that could benefit from the addition of yellow color, such as yellow, orange, orange-pink [padparadscha], and orangey-red [ruby] colors of corundum.
Irradiation of gemstones sent through the U.S. Postal Service was the other topic for Scarratt’s lab review session. In studies conducted by the GTC, with cooperation from Titan Corporation, a manufacturer of mail irradiation processors, hundreds of gems were subjected to irradiation as they would if being shipped by the Postal Service. Color changes ranged from slight to extreme, depending on the gem.
Chinese freshwater cultured pearls showed the most dramatic change. Jewelers were advised not to ship gemstones into the Washington, D.C., area, one of just a few areas where mail is being irradiated. So far, apparently only flat mail is being scanned. Therefore, registered packages should be safe “at this point,” said Scarratt. He added, however, that “should there be more terrorist activity,” more scanning units will probably be put in place and then “electron beam irradiation of mail will be a much bigger concern.”