October 24, 2002
Corundum Diffusion Treatment Due to Beryllium
The Gemological Institute of America's Gem Trade Laboratory and the American Gem Trade Association's Gemological Testing Center say they established "unequivocally" that the color change in the color-altered sapphires that entered the market early this year is caused by the diffusion of beryllium from an external source into the corundum. The labs issued a statement Oct. 21.
The gems, treated mainly in Thailand, have been the subject of extensive discussion and research including detailed analyses, replication experiments and validation by independent researchers, say the labs.
"Beryllium diffused into corundum, in an oxidizing atmosphere, at high temperatures, is the single causative agent of color change in this new process," reads the labs' statement. "Beryllium diffusion is very similar to the diffusion of titanium into corundum that creates a blue color layer, and thus both will be described similarly in our reports. The primary effect of the beryllium diffusion is an added yellow color component, although other effects have also been observed. Depending on the starting material, the colors produced by this technique now present on the market are yellow, orange, orangy pink, orange-red, green, green-blue and violet."
The labs say the majority of these treated stones can be identified through a combination of standard gemological testing techniques. They now are focusing their research efforts on establishing robust identification criteria for those stones that are not identifiable by established testing methods. They say these criteria will involve traditional gemological testing and advanced analytical techniques. "The latter will undoubtedly include instruments that are routinely used today in well-equipped gemological labs, but we are also looking at methods that historically have not been accessible to gem testing laboratories.
"Establishment of these criteria is being given the highest priority at both the GIA Gem Trade Laboratory and the AGTA Gemological Testing Center, and we will be using all of the resources at our disposal, including consultation with outside experts. We believe these efforts will help allay the concerns of dealers and jewelers alike regarding this new treatment procedure, and will allow consumers to purchase corundum with certainty and confidence," the statement concluded.