GIA and AGTA Finalize Treated Sapphire Identification
The labs will issue standard heat-treatment reports for the controversial gems
Blue sapphires exhibiting new treatment characteristics such as near-colorless rims have cropped up in the trade in the past 18 months. Reluctant to characterize them on reports until they know more about how they are treated, the Gemological Institute of Americas Gem Trade Laboratory and the American Gem Trade Associations Gemological Testing Center will identify them simply as natural sapphires that show evidence or indications of heat treatment.
When the gems turned up, the trade speculated they might be subject to a lattice-diffusion treatment, like the one used to alter the color of yellow to orange sapphires that made news last year. But investigations by various researchers, including those from GIA and AGTA, turned up no evidence of this form of treatment.
To Sri Lanka and Back
The labs made their announcements after months of intense investigation into the mystery treatment, including trips to the gem-rich island of Sri Lanka. It was from this source the colorless-rim sapphires originated. Researchers visited Punsiri Tennakoon of Punsiri Gems in Ratnapura, Sri Lanka, the proprietor of the heat treatment facility to which the treatment was traced. In analyzing his heat-treatment process, researchers discovered no evidence of intentional or inadvertent diffusion of elements from an outside source.
Hundreds of Examinations
To reach their conclusions, researchers also examined hundreds of heated and nonheated sapphires, including geuda sapphires, which vary from colorless to pale blue. Color concentrations inside the gems, as well as the near-colorless boundaries, were subjected to various forms of infrared spectroscopy and to highly sensitive chemical analysis using LA-ICP-MS and SIMS machines. While they were in Sri Lanka,
researchers also analyzed more than 20 samples before and after they were treated on the spot using the heating process at Punsiri Gems so they could document the changes that took place.
GIA says its 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.
The larger Corundum Research Group that worked on identifying the sapphires consists of a cross-section of scientists and gemologists, including George Rossman, John Emmett, Troy Douthit, Shane McClure, Christopher Smith, Mary Johnson, Matthew Hall, Wuyi Wang, Andy Shen, Michael Breeding, John Koivula, Ken Scarratt, Tom Moses, Garry Du Toit and Donna Beaton.
by Robert Weldon, G.G.
||In immersion, the new heated blue sapphires from Sri Lanka reveal unusual, billowy color concentrations. Also indicative of this phenomenon, a narrow near-colorless rim follows the contours of the inner blue color concentrations. Photo by Elizabeth Schrader/GIA.