After a year’s worth of extensive research, the Gemological Institute of America Gem Trade Lab (GTL) has concluded that the unusual color phenomenon observed in a number of heat-treated blue sapphires is a product of a specific heating regimen used by a Sri Lankan resident. “We have found no evidence of intentional or inadvertent diffusion of elements from an outside source that would require special disclosure on our gemstone reports,” GIA said in a statement. “Therefore, blue sapphires that have indications of heat treatment, as well as characteristics and properties similar to the stones examined during this research project, will be disclosed with the standard heat-treated comment and read as follows on a GIA Gem Laboratory identification report:
NATURAL SAPPHIRE, weight
Comments: Evidence of heat treatment is present.
From early on in 2003, the GIA Gem trade Lab and AGTA Gem Testing Center noticed unusual color concentrations in a number of heat-treated blue sapphires. Initially, they had great concerns about beryllium or of some other light element lattice diffusion treatment possibly entering the market under the radar of the labs.
They both launched intensive, months-long research projects that involved detailed documentation of many samples using both standard gem-testing instruments as well as highly advanced analytical techniques, (such as Laser Ablation and SIMS analysis). Gemologists also made two trips to Sri Lanka to visit Punsiri Tennakoon of Punsiri Gems, Ratnapura, Sri Lanka, who was responsible for all of the new treated gems.
They conducted heating experiments to try and understand the color-causing mechanisms behind the unusual concentrations. According to the GTL, the results required a fresh look at the changes that take place within the crystal lattice when sapphires are exposed to various heating conditions, and a reevaluation of how the GIA laboratory considers and discloses heat treatment on its corundum reports.
According to the GTL, hundreds of non-heated and heated blue sapphires were re-examined, including several different types of geuda, the colorless to white or pale blue Sri Lankan sapphires that change to an intense even blue after heat treatment. These sapphires ranged in size from 1 to 20 cts.
Numerous tests were conducted to compare the inner blue color concentrations and the outer decolorized regions of the suspect stones, including focused ultraviolet/visible/near-infrared and mid-infrared spectroscopic studies. Hundreds of highly sensitive chemical analyses involving Laser Ablation and SIMS techniques (focusing on 65 different elements) were also employed. GTL provided evidence of just one such analysis, where the gem was lasered over 180 times, with each test chemically analyzed looking for any variation from the inner blue core to the outer colorless area. No change was noted.
“Now, more than ever, GIA is committed to the colored stone industry and to addressing serious trade issues as they unfold,” the GIA statement said. “The GIA research team will continue to study the various color varieties of corundum and the effects of heat and other treatments in their ongoing efforts to refine disclosure nomenclature and anticipate future developments that might affect the corundum trade.”Follow JCK on Instagram: @jckmagazine
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