GIA Exposes Rough Diamond with Fake Green Color

RAPAPORT… Manufacturers coated a rough diamond with a green substance
to imitate a natural color, the Gemological Institute of America (GIA) said
after the stone turned up for grading.




The presence of chromium oxide powder on the surface of
the 6.49-carat crystal was a rare case, as color coatings are more common with
faceted stones than with rough, and tend to be pink, orange, red or blue, the
GIA explained. The recent episode “represents a significant attempt to
artificially reproduce the features seen on natural green diamonds,” Virginia
Schwartz, a supervisor of diamond identification, and Christopher Breeding, a
senior research scientist, wrote in a lab note in the Summer 2019 issue of Gems
& Gemology, the institute’s quarterly journal.




Most green diamonds receive their color from
radiation damage occurring in the earth’s crust over long periods of time, Schwartz
and Breeding continued. Additional radiation can leave green surface patches,
which turn brown after exposure to high temperatures. The presence of these
“stains” helps indicate the hue is authentic.




However, the stone recently submitted to the GIA’s laboratory in Carlsbad, California, for a Colored
Diamond Grading Report gave results during spectroscopic examination that did
not match the norm for a natural green diamond. The uneven color came not from
radiation marks, but from tiny emerald-green platy crystals attached to the
surface. They were removable with tweezers or a pointer probe, but not when
wiped with a cloth.




Further testing confirmed the identity of the powder,
which workers had heated to about 700 degrees Celsius to produce crystallized
plates that resembled genuine radiation stains, the GIA theorized.




“While the unique coating is easily discerned from
natural green radiation stains under magnification, this stone is a strong
reminder to carefully examine any green diamond, even rough crystals, in order
to know exactly what you are buying,” Schwartz and Breeding concluded.




Image: The 6.49-carat rough diamond with an artificial green surface color. (Diego Sanchez/GIA)