Figure 1: In the past several months, the GIA Gem Laboratory has examined dozens of blue sapphires that showed clear evidence of high-temperature heat treatment as well as unusual color concentrations. The stones have ranged from 1 to about 20 cts. The face-up appearance of these two 3-ct. samples is representative of the material. Photo by Maha Tannous.

Figure 2: In immersion, these heated blue sapphires reveal unusual, billowy color concentrations. Also indicative of this phenomenon, a narrow near-colorless boundary follows the contours of the inner blue color concentration. Photo by Elizabeth Schrader.

Figure 3: Tthese unusual color concentrations commonly display a scalloped edge at the boundary with the colorless region. Note, however, that the parallel growth planes extend across both the inner and outer color zones without interruption, except that the color becomes abruptly lighter or less saturated. Photomicrograph by Shane McClure.

Figure 4: One hundred eighty-seven spot analyses were taken by LA-ICP-MS to map the full chemical composition of this sample. No systematic chemical variation was recorded between the inner blue color concentration and the outer decolorized region. Photo by Wuyi Wang.

When, early in 2003, gemologists from the GIA and AGTA laboratories first noticed unusual color concentrations in a number of heat-treated blue sapphires, they were concerned that this might be a new form of treatment (figures1–3). In response, they launched an intensive, months-long research project that involved detailed documentation of many samples using standard gemological instrumentation and highly advanced analytical techniques. The researchers also took two trips to Sri Lanka to visit the proprietor of the heating process and conduct heating experiments to understand better the color-causing mechanisms behind the unusual concentrations. 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.

Hundreds of non-heated and heated blue sapphires were involved in this research, including several different types of geuda, the colorless to white or pale blue starting material. Numerous tests were conducted to compare the inner blue color concentrations and the outer decolorized regions of the suspect stones. These included focused ultraviolet/visible/near-infrared and mid-infrared spectroscopic studies, as well as hundreds of highly sensitive chemical analyses involving laser ablation– inductively coupled plasma–mass spectrometry (LA-ICP-MS) and secondary ion mass spectrometry (SIMS) techniques (focusing on 65 different elements; figure 4). In addition, during the course of two research trips to Sri Lanka to investigate the specific heating process, more than 20 samples were analyzed before and after heat treatment to document the changes that took place.

As a result of this extensive research, GIA has concluded that the color phenomenon observed in these stones is a product of the specific heating regimen used by Mr. Punsiri Tennakoon of Punsiri Gems, Ratnapura, Sri Lanka. 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. 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.

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