The International Colored Gemstone Association in its first Lab Alert for 2004 has informed gemologists and members of the colored stone trade about the findings of two leading gemological laboratories. The labs concurred that they had found no evidence of diffusion in a batch of heated blue Sri Lankan sapphires that were heat treated by the same source.
The testing by the SSEF-Swiss Gemological Institute of Basel, Switzerland, and the Gemological Institute of America followed recent reports in the trade media, in which it was suggested that a new heating process for blue sapphire from Sri Lanka may involve “lattice diffusion.” GIA is not ruling out however, that they may find some type of lattice diffusion invloved in the new process.
Joseph M. Menzie, ICA president, said that its first priority is to protect the consumer. However, when a false alarm is raised, ICA also needs to act and inform.
“In this most recent case, early reports suggested that a new heating process involved diffusion,” Menzie said. “Thus far, such charges have proven unfounded, and, in fact, reasonable explanations have been put forward to explain what is being observed.”
Menzie noted that the representatives of SSEF and GIA had researched stones that were heated using this particular process and both parties had come to the same conclusion—”that there is no evidence at this point in time that any foreign elements, which may point to diffusion, were involved.” That said, GIA would prefer not to make this lack of evidence a final conclusion, since they are still uncertain whether or not any lattice diffusion or foreign elements are invloved. SSEF’s research team even suggested that the colorless rims on the surface of the stones were caused by a technical oversight in the heating process, during which a minor degree of oxidization occurred—causing surface de-colorization. The fact that the surfaces of the cut sapphires that were originally studied were not uniformly decolorized was because the stones had been heat treated as rough, and therefore, most of oxidized areas had been polished away.