April 16, 2004
GIA to Issue "Standard Heat Treatment" Reports for Controversial Sapphire Treatment
The Gemological Institute of America's Gem Trade Laboratory researchers say they are reviewing changes that take place in the crystal lattice of sapphire when exposed to various heating conditions. A press release also says GIA is "reevaluating how the GIA Laboratory considers and discloses heat treatments on its corundum reports." GIA says it will now issue standard heat treatment reports on stones whose characteristics coincide with their most recent findings. Reports will say:
"NATURAL SAPPHIRE, [weight]
Comments: Evidence of heat treatment is present"
Approximately a year ago, unusual sapphires with "colorless rims" especially when viewed submersed in methylene iodide began to appear in the trade. The treatment raised speculation these might be subjected to a hitherto unknown lattice diffusion technique. Months later, the American Gem Trade Association's Gem Trade Laboratory noted it had not discovered any form of lattice diffusion in the sapphires, but concluded the stones showed diagnostic characteristics of heat treatment.
GIA's fresh stance on corundum heat treatments follows months of intense investigations, including trips to the gem-rich island of Sri Lanka. It was from this source that the first colorless rim sapphires originated. GIA now describes the stones as exhibiting "near colorless boundaries." GIA researchers visited Punsiri Tennakoon, of Punsiri Gems in Ratnapura, Sri Lanka, the proprietor of the heat treatment facility. In analyzing his heat treatment process, researchers discovered no evidence of intentional or inadvertent diffusion of elements from an outside source. Separately, hundreds of sapphires were examined including "geuda" sapphires, which vary from colorless to pale blue. Color concentrations inside the stones, as well as the near-colorless boundaries were subjected to various forms of infrared spectroscopy, as well as highly sensitive chemical analysis using LA-ICP-MS and SIMS machines. Before and after treatment stones were also examined.
For sapphire dealers, the findings may provide a sense of relief, due to the potential adverse effect a different report comment could have on the perceived value of the stone. No other labs have issued reports on the sapphire treatment.
by Robert Weldon, G.G.