Gemstones & Pearls/News
AGTA Describes Emerging
Treated gems exhibit unique and inexplicable characteristics
The American Gem Trade Association says its Gemological Testing Center is seeing some blue sapphires with indications of heat treatment. AGTA doesnt know exactly what the treatment entails or how it changes the appearance of sapphires. AGTA says the stones exhibit other characteristics that are unique and cannot be fully explained.
Gemological tests to identify the treated sapphires include:
- Microscopy: Observing the sapphire through a microscope often allows identification of distinctive color zoning and inclusion features indicative of heat treatment. By itself this observation isnt diagnostic of the new treatment, however.
- Immersion in MI Liquid: Immersing the stones in methylene iodide and observing them against diffused white lighting allows a pale blue to near-colorless layer to appear closely following the girdle outline. This characteristic cant be explained yet. The colorless rim hasnt been observed in natural untreated sapphires. Those that exhibit this rim should be submitted to a qualified lab for further confirmation.
Ken Scarratt, AGTA/GTCs lab director, and colleague John Emmett are studying the sapphire treatment in New York City, aided by Sri Lankan treaters reported to be using the technique. Weve asked them to show us more samples and to explain their technique, says Douglas Hucker, AGTAs 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 on sample gems hasnt revealed the presence of beryllium (beryllium lattice-diffusion treatment can cause color changes in some sapphires and has been the subject of controversy in the trade). The possibility this is a new form of lattice diffusion hasnt been ruled out because such treatment takes place in an environment of intense heat. However, beryllium as a medium to cause color change appears not to play a role in the new treatment.
by Robert Weldon, G.G.
||If you immerse the treated sapphire in methyene iodide liquid and examine it against diffused white lighting, you see a nearly colorless rim around the outline. Courtesy of AGTA/GTC, New York City.