GIA Exposes Rough with Fake Green Color

RAPAPORT... Manufacturers coated a rough diamond with a green substanceto imitate a natural color, the Gemological Institute of America (GIA) saidafter the stone turned up for grading.The presence of chromium oxide powder on the surface ofthe 6.49-carat crystal was a rare case, as color coatings are more common withfaceted stones than with rough, and tend to be pink, orange, red or blue, theGIA explained. The recent episode "represents a significant attempt toartificially reproduce the features seen on natural green diamonds," VirginiaSchwartz, a supervisor of diamond identification, and Christopher Breeding, asenior 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 fromradiation damage occurring in the earth's crust over long periods of time, Schwartzand 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 ColoredDiamond Grading Report gave results during spectroscopic examination that didnot match the norm for a natural green diamond. The uneven color came not fromradiation marks, but from tiny emerald-green platy crystals attached to thesurface. They were removable with tweezers or a pointer probe, but not whenwiped with a cloth.Further testing confirmed the identity of the powder,which workers had heated to about 700 degrees Celsius to produce crystallizedplates that resembled genuine radiation stains, the GIA theorized."While the unique coating is easily discerned fromnatural green radiation stains under magnification, this stone is a strongreminder to carefully examine any green diamond, even rough crystals, in orderto 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)