The previously unknown treatment that temporarily boosts a diamond’s color has also been discovered on diamonds submitted to the Antwerp branch of the International Gemological Institute, according to a report being released today in Israeli newsletter Diamond Intelligence Briefing.
On May 13, GIA said it suspected that as many as 500 stones had been treated with a mystery process that temporarily boosted a diamond’s color several grades.
In his article, author Chaim Even-Zohar says that IGI gemologists have determined that the mystery treatment is, in fact, a coating, but they don’t know its chemical composition. The coating may involve an extremely thin film that may be visible only at 500 times magnification.
The coating can be reversed by acid boiling, but it is not clear whether it is the acid or heat that affects the treatment, the report says.
Making things more complicated, the stones that arrived at IGI and GIA do not appear to have come from the same source, according to the report.
At a recent panel at JCK Las Vegas, GIA said it was “close” to determining the mystery 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.