A recent article was released about tanzanite, we thought we would share. Rest assured that ALL tanzanite sold at OldCities.com has been tested and is 100% natural and has not been coated. We are merely sharing the article to make you aware of this new process people are using to up the value of a tanzanite.
ARTICLE POSTED MAY 27, 2008
Two gemological labs that specialize in colored-gemstone identification have identified a new, non-permanent type of tanzanite treatment that requires disclosure at the point of sale.
The American Gem Trade Association Gemological Testing Center (AGTA-GTC) and American Gemological Laboratories (AGL) recently received faceted tanzanite samples that were later determined to have been coated.
Evan Caplan of Omi Gems sent samples to several labs after a light repolishing of a few stones resulted in a noticeable loss of color.
"Until now, we had not identified a coating on tanzanite to improve its color," AGTA-GTC Director Lore Kiefert said in a release issued on Friday.
The treatment is not immediately obvious, but careful examination with a microscope and in immersion provided clear indications of the coating in most instances, said Christopher Smith, vice president and chief gemologist of AGL.
"This was evidenced by abrasions along facet junctions and at the culet where the coating had worn off, as well as a subtle iridescence when viewing the surface with reflected light," Smith said.
Advanced analytical testing pinpointed that the coating contained cobalt.
"The most reliable means to substantiate the presence of the coating is the use of X-ray fluorescence spectroscopy," Kiefert said, adding that the cobalt is readily detected through that particular analytical technique.
Although the gemstone industry has become very familiar with the practice of heating tanzanite to achieve the best violet to blue color, the color-enhancing coating on tanzanite has not been seen before.
The majority of the tanzanite sample was composed of smaller calibrated stones. Fine color tanzanite in this size range is rarely sent to a lab and therefore would ordinarily avoid detection unless closely scrutinized.
"This is just another reminder that each and every gemstone should be fully examined to determine whether or not it has been treated," Smith said. "Today, it is not uncommon to see stones that have been treated using multiple or compound techniques to achieve a particular result."
Both Kiefert and Smith emphasized that any treatment used to modify the color of a gem should be disclosed. Coatings, in particular, are not considered permanent and in the United States are required by Federal Trade Commission guidelines to be properly disclosed at the point of sale.
2 comments:
Thje issue of coating is a reall concenr for us in the industry as it has the effect of turning an erstwhile unblemished stone into one that consumers will be wary of. The fact that only a tiny percentage of Tanzanite has been treated and that these tend to be the small calibrated stones which generally lack color anyway is little reported. The industry must tackle this problem head on and reassure consumers otherwise it will face a crisis of confidence much like emerald did for years due to its oiling and heavy treatments. More info on the coating here : http://www.lapigems.com/tanzanite_stone.asp
http://www.lapigems.com/tanzanite_stone.asp
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