Mystery Sapphire Treatment Unmasked

After the sapphire treatment, the resulting color is pink with a subtle orange – a padparadscha color that is very much desired by dealers. Photo © AGTA.

By Marlene A. Prost

NEW YORK — Gemologists have decoded the mysterious process used in Thailand to change pink sapphire to pink-orange shades resembling rare padparadscha.

Beryllium appears to be the key element responsible for the color change, which also causes colorless sapphires to turn yellow and dark red-purple sapphires to turn a vivid red. The process has been successfully replicated by several researchers, including scientists at Swarovski & Co. in Austria and corundum heating expert John Emmett, Ph.D., of Crystal Chemistry.

"What's actually happening is beryllium is being diffused into the stone from the outside and creating an environment in a host chemistry that gives the [orange] color," explained Kenneth Scarratt of the American Gem Trade Association Gemological Testing Center (AGTA GTC). The beryllium adds a yellow color to the surface of the gems, which appears orange in pink sapphires.

As a result of this discovery, the AGTA GTC and the GIA have changed the terminology they will use when issuing identification reports on these gems. For one thing, the labs will now use the technical term "bulk diffusion" instead of surface diffusion or diffusion treatment for all processes that involve introducing a color-changing element into the gem, regardless of the method.

Under the new policy, the reports will state that the corundum has "indications of heating and of surface-related color created by bulk diffusion."

In some cases, the heating process causes the surface of the sapphires to melt and then recrystallize. In cases where the recrystallized sapphire is not polished off, the report will note "indications of heating and of surface-related color created by bulk diffusion; areas of synthetic overgrowth are present."

The terminology was developed at a meeting of four gemological laboratories: AGTA GTC, GIA, Swiss Gemmological Institute (SSEF), and the Gemological Institute of Thailand. At press time, only the AGTA GTC and the GIA were planning to use the above descriptions.

Experiments are continuing to determine the mechanics of the process. Emmett notes that while "We believe that beryllium is the causative agent of the yellow color, we have not ruled out the diffusion of other elements that may also have an important effect."

Swarovski & Co. also has replicated the process, and has released some details of its research. They were able to produce the yellow to orange coloration in pink sapphire from Madagascar. They also experimented with blue, yellow-green, and dark red corundum from Songea. The blue and yellow-green material turned yellow; the dark red turned orange-red; and the pink turned orange.

Swarovski is holding off on plans to produce and market sapphires treated with this process because the market has "too much confusion and uncertainty," says Kahler. Swarovski's managing director in Japan, a prime market for orange sapphire, reports that there is enormous concern in Japan about the difference between these treated sapphires and natural padparadscha.

In the United States, too, few dealers will knowingly carry these sapphires, in part due to the dreaded "diffusion" designation and in part due to the current limited market for the material.

For an expanded version of this report, see the July/August 2002 issue of Colored Stone.

Posted: June 11, 2002