Cobalt-Colored Composite Sapphires Now Entering the Market

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28 January 2013: NEW YORK – American Gemological Laboratories (AGL): Gemstone treatments are a regular issue which the gemstone trade has to contend with. In May 2012, AGL first learned of a new type of treated sapphire which was becoming available in the Bangkok market “This treatment was first described to me as a new type of lead-glass treated corundum where a blue colorant was also introduced.” indicated Christopher P. Smith, President of AGL.

In November and December of 2012, clients of the AGL contacted the lab indicating that such stones were starting to be encountered in the marketplace. Recently a couple of samples were sent to the AGL by Dr. Cigdem Lule of GemWorld International Inc. Although the stones appeared fairly transparent and had a convincing “blue sapphire” color, color concentrations were readily visible upon closer scrutiny even with the unaided eye and were obvious with magnification using a 10x loupe or microscope (figure 1 below).

“A chemical analysis readily showed a high concentration of lead in addition to the aluminum oxide of corundum, with trace elements of iron and gallium, while a visible spectrum revealed absorption bands associated with cobalt.” Smith stated (figure 2 below).