Labs Avoid Diffusion Description for New Corundum Treatment


February 28, 2002

Labs Avoid Diffusion Description for New Corundum Treatment

Four of the leading gemological laboratories in the world have agreed to not use the term "diffusion" when describing a new corundum treatment, even though the treatment appears to involve what the trade traditionally called diffusion (GIA Releases New Corundum Treatment Report). The treatment surfaced in Thailand earlier this year.

The AGTA Gemological Testing Center, the Gemological Institute of America's Gem Trade Laboratory, the Gubelin Gem Lab and the SSEF Swiss Gemmological Institute announced the joint agreement in late February.

The labs concluded this new treatment of corundum – used primarily to produce an orange component in pink sapphires from Madagascar – probably is a form of diffusion, though the effects differ from diffusion treatments seen in the past. Also, research uncovered new forms of diffusion, making use of the broad term "diffusion" problematic when describing this particular form of the treatment.

Gems subjected to the new treatment appear similar to other treated corundum gems that were surface diffused with chemicals, notably blue sapphires diffused with iron and titanium compounds. Some samples of the newly treated gems, however, feature a color penetration much deeper than previous shallow color concentrations. Also, the labs say routine chemical analyses don't readily identify color-causing elements found in other diffused corundums, such as titanium or chromium. Some advanced analytical testing indicates smaller amounts of lighter elements, such as beryllium, may be responsible for the induced orange hue.

Up to now, not all labs distinguished between surface diffusion and other possible forms of diffusion. The consortium of labs will forgo the term diffusion completely, calling it "lacking, both in terms of technical accuracy and descriptive purpose."

Instead the labs will describe the new diffused sapphires as "treated (orange) sapphires" when labeling this variety of the corundum species in reports. In the comments section of the report, the labs agreed to run the statement: "Indications of heating. The orange coloration of this stone is confined to a surface-related layer." The labs also agreed sapphires altered using this treatment to imitate padparadscha color cannot be labeled as padparadscha.

In a question-and-answer section that accompanies the labs' announcement, they state labeling the stones as "treated (orange) sapphires" will easily separate them from sapphires that do not have a surface-related layer of color. Adding the sentence that the orange coloration is "confined to a surface-related layer" distinguishes this from orange color zones that may result in the interior of sapphires subjected to traditional heat treatment or may naturally occur in unheated sapphires. The comments also will help disclose to buyers the color is likely to change if the stone is re-cut for any reason.

The labs' move to avoid the term diffusion concerns many in the industry. "Do we need new nomenclature for these stones?" asks Richard Hughes, an associate at Pala International, Fallbrook, CA. "I don't think so."

The effect of such a word change on the perception of some sapphire treatments could be enormous, say critics. No longer labeling a surface-diffused stone as such, for example, could lessen the stigma attached to this form of treatment – a possibility dealers of natural gems say they find abhorrent. "It's a very scary blurring of the lines that were once drawn to define [certain] treated stones," says Bill Larson, president of Pala International.

– by Robert Weldon, G.G.

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