The following brief appears courtesy of Gems & Gemology‘s G&G eBrief
Image courtesy of Gems & Gemology. Photo by Robison McMurtry
Author: Sally Eaton-Magana (GIA Laboratory, Carlsbad)
Diamonds have been coated pink with techniques ranging from the simple ancient practice of “painting” a stone to the application of sophisticated thin films. The Carlsbad lab recently received a 1.50 ct heart shape and a 1.68 ct pear shape that initially appeared the equivalent of Fancy pink and Fancy Light pink, respectively. FTIR and photoluminescence spectroscopy showed they were type IIa pink diamonds, but their UV-Vis spectra were anomalous for such stones, with peaks centered at about 505 and 540 nm rather than a broad band centered at 550 nm.
Microscopic observation revealed a nearly imperceptible trace of reddish residue on a natural of one of the diamonds. After both were thoroughly cleaned in soapy water and, ultimately, acetone, they were noticeably lighter in color, which indicated they had been treated with a coating that was removed by such solvents. The cleaned diamonds showed the expected UV-Vis spectra. When they were color graded without the coating, the heart shape was Very Light pink and the pear shape Faint pink — a decrease of several color grades for both.
The diamonds were undoubtedly coated to intensify their pink color, likely with the knowledge that the coating would not be permanent — but hoping it would at least last through the grading process.
GIA Laboratory, Carlsbad