Feature Gems & Gemology, Spring 2005, Volume 41, No. 1

Coated Pink Diamond — A Cautionary Tale

The Diamond Trading Company (DTC) Research Centre had the opportunity to examine a diamond that, on submission to a commercial gem laboratory, was stated to have been HPHT treated. However, spectroscopic analysis yielded data inconsistent with this statement. After further testing, it was determined that this diamond, which originally was probably pale yellow, had been coated to change its color to the equivalent of Fancy Intense purple-pink. Careful examination with a microscope revealed evidence of a coating exclusively on the pavilion facets. Elemental analysis of the coating suggests it may be calcium fluoride with a gold impurity that was added either to generate the absorption responsible for the pink color or to assist as a nucleating agent for the calcium fluoride film.