October 10, 2003
AGTA Describes Emerging Sapphire Treatment
The American Gem Trade Association issued a Gemstone Update saying its Gemological Testing Center says it is seeing some blue sapphires reaching the U.S. market that exhibit indications of heat treatment. AGTA says it's necessary to alert the trade, despite not knowing exactly what the treatment entails or the mechanics of how it changes the appearance of sapphires. AGTA says the stones also exhibit other characteristics that are unique and cannot be fully explained at this time.
Gemological tests to indentify the treated sapphires include:
Microscopy: Observing the sapphire through a microscope one can often identify distinctive color zoning and inclusion features that are indicative of heat treatment. This observation, by itself, is not diagnostic of the new treatment. It only indicates heat treatment may have taken place.
Immersion in MI Liquid: When immersing the stones in methylene iodide, and observing them against diffused white lighting, a pale blue to near-colorless layer appears, closely following the girdle outline. This is the characteristic of the new treatment that cannot yet be explained. This colorless rim has not been observed in natural (untreated) sapphires. Sapphires that exhibit this distinct colorless/near-colorless rim should be submitted to a qualified lab for further confirmation.
Ken Scarratt, AGTA/GTC's lab director, and colleague and corundum expert John Emmett are studying the sapphire treatment in New York City, aided by Sri Lankan treaters alleged to be employing the technique. "We've asked them to show us more samples and to explain their technique," says Douglas Hucker, AGTA's executive director. "We are collecting data to record and identify what is taking place. That way we will be able to provide full information at a forthcoming date."
AGTA says SIMS testing carried out on sample gems has not revealed the presence of beryllium beryllium lattice diffusion treatment in some sapphires caused dramatic color changes in some sapphires and has been the subject of controversy in the trade. The possibility that this is a new form of lattice diffusion has not been ruled out, as lattice diffusion takes place in an environment of intense heat. However, beryllium as a medium to cause color change appears not to play a role in this new treatment.
by Robert Weldon, G.G.