Sapphires ‘Heat Treated with Additives’

Ted Themelis, research gemologist, author, and corundum expert in Thailand, would like to excise the term “bulk diffusion” from the gemological vocabulary. Bulk diffusion refers to the heat treatment that infuses foreign elements that can affect color change in corundum.

“There is no need to introduce the unpopular—but scientifically correct—bulk-diffusion term, which refers to ion transportation phenomenology applied to all treated gems,” Themelis says. “Jewelers and gem dealers are not scientists but gem traders seeking easy communication that properly represents the product they sell.”

Here is Themelis’s proposed disclosure statement:

Gem species: Natural Corundum

Enhancement: Enhanced by heat

Treatment classification: HEAT-TREATED (with additives)*

Comments: *Additive compounds including beryllium-bearing substances may have been used in the process. The resulting color may be distributed in a non-uniform pattern, and color may be removed or altered if the stone is damaged or after repolishing.

“I have received great positive response from the gemological community,” says Themelis. “Of course, the above disclosure statement is subject to further modifications.”

Cooking class. For those looking for a hands-on way to understand the issue, Themelis is offering a 48-hour, $1,100 course in corundum enhancement at his Bangkok laboratory, Feb. 24-28, 2003.

The course covers a wide range of topics and includes practical application labs. For more information about Themelis and his research, log onto