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Diffusion Sapphire Study Continues

New research has shed further light on the controversial sapphire treatment being called "bulk diffusion."

The treatment adds yellow to sapphire, turning pink sapphires orange and brightening dark red or purple sapphires. Two experts in the field of heat-treating, John Emmett and Troy Douthit of Crystal Chemistry, have experimentally confirmed that beryllium is the sole agent responsible for the color change. Their report on their findings was published on the American Gem Trade Association (AGTA) Web site.

Emmett and Douthit conducted a series of experiments on various types of sapphire, including sapphire that had already been heat-treated. They heated sapphire with beryllium alone, magnesium alone, and no added elements; only the sapphire heated with beryllium showed the characteristic bright yellows and oranges of the bulk diffusion process.

When testing beryllium in high-purity, colorless synthetic sapphire, Emmett and Douthit found that the color tended to change to brown rather than yellow. A similar result was reported by Henry Hänni of the Swiss Gemmological Institute (SSEF) in Basel, Switzerland. The beryllium seems to be reacting with one of the other elements in the sapphire to produce the yellow color. In a presentation to Thai gem traders in late July, Hänni suggested that the culprit was titanium; Emmett and Douthit believe it may be silicon.

Theorizing that the color change is caused when the beryllium being diffused into the gem displaces atoms that were molecularly bonded there, Adolf Peretti of GemResearch Swisslab has proposed the treatment be called enhancement by internal migration, or E(IM). The term has broad support in the Thai gem community, where traders are anxious to avoid the dreaded "diffusion" label.

International fears about the treatment have taken their toll on the Thai sapphire market, especially since it appears the gems have been sold without disclosure for the past one to two years. If a gem is completely diffused with beryllium — producing an even color — the only way to detect the treatment is to use high-tech equipment found mostly at specialized research facilities. No gemological laboratory in the world currently has such equipment onsite, although several of them routinely rent research time from other laboratories.

Posted: October 8, 2002

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