GTL Calls Suspect Blue Sapphires ‘Heat Treated’

After a year of extensive research, GIA’s Gem Trade Laboratory (GTL) has concluded that the color variation observed in a number of heat-treated blue sapphires is simply a product of the specific heating regimen used by one Sri Lankan lab operator, Punsiri Tennakoon. A GTL press release dated April 14 states, “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.”

These gems will be disclosed with GTL’s standard “heat-treated” comment, which will read as follows on a GIA GTL identification report: “NATURAL SAPPHIRE, [weight]. Comments: Evidence of heat treatment is present.”

Suspect sapphires. Early in 2003, GTL, AGTA’s Gem Testing Center laboratory, and the SSEF laboratory in Basel, Switzerland, all noticed unusual color concentrations in a number of heat-treated blue sapphires. (See Gem Notes, “New Sapphire Enhancements Could Spell Blue Christmas,” JCK, December 2003, p. 26; and “No Indication of Diffusion? Maybe … Maybe Not,” JCK, April 2004, p. 36.) Initially, the labs were concerned that gems that had undergone beryllium-lattice-diffusion treatment (or other light-element-lattice-diffusion treatment) might enter the market under their radar.

Both labs 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 inductively coupled plasma mass spectrometry (LA-ICP-MS) and secondary ion mass spectrometry (SIMS). 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 to understand the color-causing mechanisms behind the unusual concentrations. According to 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 GTL, hundreds of unheated and heated blue sapphires were reexamined, including several different types of geuda, the industrial-appearing translucent colorless to yellowish-white or pale blue Sri Lankan sapphires that change to transparent gemmy, intense medium to dark even blue after heat treatment. These sapphires ranged in size from 1 to 20 carats.

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 LA-ICP-MS and SIMS techniques (focusing on 65 different elements) also were employed. GTL provided evidence of just one such analysis, where the gem was lasered more than 180 times, with each test chemically analyzed to look for any variation from the inner blue core to the outer colorless area. No change was noted, eliminating all of the known possibilities.

“Now, more than ever, GIA is committed to the colored stone industry and to addressing serious trade issues as they unfold,” said the GIA statement. “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.”—