April 28, 2004
AGTA GTC to Issue "Standard Heat Treatment" Reports
The American Gem Trade Association's Gem Testing Center says it will use standard disclosure terminology for Sri Lankan sapphires it has been investigating over the past year. These sapphires exhibited an unusual color distribution at first described as "near colorless rim." It was not known what caused the unusual color distribution to occur.
Early on, AGTA GTC ruled out beryllium diffusion as a potential mechanism causing the unusual color distribution, but said it could not rule out other forms of lattice diffusion.
A corundum research group, of which AGTA GTC is part, recently concluded that the "color distribution is the product of the specific heating regimen used by gemstone treaters in Sri Lanka." It added: "We have found no evidence of intentional or inadvertent diffusion of elements from an external source that would require separate disclosure." Consequently, AGTA GTC's reports on this particular kind of Sri Lankan heat-treated sapphires will now say, "Indications of heating."
Last week, the Gemological Institute of America revealed similar information and also said it would use similar terminology on its reports.
The Corundum Research Group consists of a cross-section of scientists and gemologists, including Professor George Rossman, Dr. John Emmett, Troy Douthit, Shane McClure, Christopher Smith, Dr. Mary Johnson, Matthew Hall, Dr. Wuyi Wang, Dr. Andy Shen, Dr. Michael Breeding, John Koivula, Ken Scarratt, Tom Moses, Garry Du Toit and Donna Beaton.
For more background, go to Professional Jeweler, December 2003, "AGTA Describes Emerging Sapphire Treatment."
by Robert Weldon, G.G.