The GIA's Bangkok Research Lab has updated their research on the heating of Mozambique tourmaline, finding that simple heating to 700°C with no additives changes yellow staining in fissures to a red color. The changes are often quite dramatic. In some cases, fissures, fractures, growth tubes and other surface-reaching openings showed no discernible yellow staining prior to heating, but after heating still turned red to purple. It is possible that these fissures contained natural contaminants, but not in great enough concentration to be easily visible prior to heating. It is also possible that the heating mobilizes the contaminants. In any event, this type of heating actually disfigures the stones, producing and enlarging fractures and making the stones uglier in overall color.
The causes of these heat-produced stains is still under investigation, but is thought to involve the conversion of limonite to hematite. That they have been found in stones that were not previously heat treated suggests that they are the result of contaminants that entered the gem naturally and were altered after the gems were heated.
In some cases, staining from the openings appeared to bleed into the body of the gem, but it is still uncertain if this is a result of an optical illusion resulting from blurring of focal points above and below the fissures or if it represents actually bleeding of color into the body of the stone.
This phenomena appears to be separate from the pink coloration that appears to be associated with natural radiation staining from what is believed to be invasion of uranium and thorium-bearing impurities while the crystals were in the ground. This is also discussed in the same paper.
Their conclusion regarding the latter is as follows:
"Clearly more specimens need to be analyzed before a better understanding of the mechanisms involved is achieved, however is would appear that an alternative and more likely cause for these color concentrations in tourmaline has now been firmly established. Certainly the assumption that these color concentrations are produced artificially by one of the diffusion processes has been put to question and been found to be lacking in substance."
Heating was performed by John Emmett (and possibly Troy Douthit), with the analytical research/testing done by the GIA Research Lab in Bangkok, under the direction of Ken Scarratt and Sudarat Saeseaw. Specimens were provided by NCS Group (the company I work for in Thailand), along with Miranda Gems of Hong Kong, which is the biggest miner of Mozambique paraíba tourmaline.
Note to all: This version of the GIA's ongoing research was uploaded to their website on July 28, 2009. See also this article from GIT, which was posted in July 2009, prior to the GIA update:
Postscript: Although the GIA paper doesn't specifically mention it, there was no evidence that the stones tested were either synthetic tourmaline or diffusion-treated tsavorite masquerading as synthetic tourmaline. There is also no evidence that buying tourmalines from Thailand will foster hair growth on the palms, but this question probably deserves further study. Or perhaps just a show of hands would do.
Post subject: Re: Update on GIA's Heating of Mozambique Tourmaline
Posted: Sun Aug 02, 2009 11:03 am
Valued Contributor
Joined: Sun Mar 08, 2009 2:16 pm Posts: 331
Richard Hughes wrote:
Postscript: Although the GIA paper doesn't specifically mention it, there was no evidence that the stones tested were either synthetic tourmaline or diffusion-treated tsavorite masquerading as synthetic tourmaline. There is also no evidence that buying tourmalines from Thailand will foster hair growth on the palms, but this question probably deserves further study. Or perhaps just a show of hands would do.
So here I am in this cyber coffee shop in town and I read Dick's postscript. .... several people were startled by my outburst. Thanks for this update and the good laugh.
Joined: Thu Sep 25, 2008 10:33 am Posts: 840 Location: Mars PA
Its too hairy for me to show, but I will try and clap for continuing to get the research done to limit the damage done by irresponcible accursations concerning Mozambique tourmaline.
I hope that some positive comes out of this research in the area of a definitive set of observations that can say whether a Mozambique tourmaline has been heated or not by man.
Well are we really surprised? Weren't we all aware that the "crud in the tubes" is and was a last ditch effort on the part of Messieurs James and Federman to save the crumbling edifice built of absurd claims, silly salvos and hackneyed hyperbole.
Well the science has spoken, and as I suggested before, Mr. James should have quit with andesine, by the time the dust cleared and the real science came out, few would have noticed that his methodology and conclusions just didn't hold up.
Hubris and tabloid journalism make for a potent combination and a heady brew, but eventually the truth has a way of getting out.
Excellent report...Thanks Richard It's nice to see there is a simple explanation that doesn't invoke the diffusion devil (he gets enough press as it is)
Users browsing this forum: No registered users and 8 guests
You cannot post new topics in this forum You cannot reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You cannot post attachments in this forum