Report finds mystery diamond treatment at IGI

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In recent months, diamonds have been submitted to the Gemological Institute of America (GIA) and the International Gemological Institute (IGI) that have been treated with a chemical coating in order to temporarily boost their colour by several grades.

On May 13, GIA reported its suspicions that as many as 500 stones had been subject to this mystery process. Gemologists at IGI are still unsure about the chemical composition of the coating, but believe it to involve an extremely thin film that may only be visible at 500 times magnification. The coating may be removed by acid boiling, but it is unclear whether it is the acid or the heat that reverses the treatment.

“We know what is being done, but we don’t know how it is being done,” said Phil Yantzer, vice-president of GIA’s Carlsbad lab services.

The stones that arrived at IGI and GIA do not appear to have come from the same source. At a recent panel at JCK Las Vegas, GIA said it was “close” to determining the nature of the mystery treatment. CJ

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