Gem FAQS > Gemstone & Jewelry News & Updates > July 2010- Diamond Coatings.

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This Very Light pink heart-shaped diamond was submitted to the lab with a coating that gave it a Fancy pink color appearance, similar to the stone in the inset. Photo by Robison McMurtry.
‘Fancy’ Pink Diamonds Revealed as Coated Pale Pinks
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.

- Sally Eaton-Magana
GIA Laboratory, Carlsbad

Last updated on January 16, 2012 by Francis M Lynch