The Gemological Institute of America’s Gem Trade Lab (GTL) and the American Gem Trade Association’s Gem Testing Center (GTC) have announced progress in identifying bulk-diffusion-treated sapphires coming from Chanthaburi, Thailand. It now appears that much of this new material can be identified with standard gemological tests.
Gemologists will have to use magnification, immersion, and possibly visible spectrum. “We’re looking for color distribution, primarily,” says Ken Scarratt, GTC’s director in New York. “Surface conformal zoning. We do see this in a lot of these stones.” The layer is difficult to find in the new stones, even under immersion. “In some cases, the color zoning is really quite deep, but it is still there,” says Scarratt.
In addition, heated inclusions may be indicators, and the visible spectrum also might offer clues. Meanwhile, other gemological tests are being investigated. Infrared spectrum analysis may be useful in finding an indication of treatment, says Scarratt, who noted that infrared is “standard gem testing equipment” for the professional gem lab.
The stones can be identified by secondary ion mass spectrometry (SIMS), but that can cost $500 to $700 or more per stone. Labs use SIMS analysis to look for beryllium, which has been identified as the coloring agent.