Coated Tanzanite?

[LD]

About a year ago I was warned that a new coated tanzanite was seeping into the market in Thailand. The process involves something along the lines of the old style BBD process as it''s unstable and apparently when scratched reveals the white of the very poor quality tanzanite beneath.

Fast foward 12 months and he tells me that the market is awash with the gemstones. Today I met a friend who works in the UK and is in a position to see lots of gemstones. Apparently the first coated Tanzanite has appeared and was sold to an unsuspecting buyer as natural Tanzanite.

Just wondering if anybody has seen it, if it''s in the US yet and whether I''m correct about the treatment being used?

 

[lavenderlill]

Wild Fish Gems reports on their website, "Cobalt coated tanzanite was found by the GIA. Tanzanite is always heated into permanent color change but this "color" can be scratched off." That''s the extent of what I have heard to date.

 

[lavenderlill]

This just in...I realized there is also an article about this in the May/June 2008 issue of Colored Stone Magazine. Not too much more information than you seem to already have but you can read it online if you''re interested.

 

[Harriet]

One of my dealers told me that you can check by looking at the culet.

 

[Richard M.]

A better test is to be very skeptical of 3 to 5 mm. tanzanite stones with top color. Transparent gem material is like water. Shallow water doesn''t have much color but the deeper it gets, the more color it shows. Small colored gems of any type are usually not as richly colored as larger ones.

Some Thai dealers began coating smaller tanzies to overcome that marketing problem. Richly-colored uncoated small tanzanites do exist but not in abundance. Close examination of facet junctions and the culet areas of some stones MAY reveal areas where the coating has been worn away. But not all coated stones offer those clues and more advanced microscopic and spectroscopic tests are recommended.

Warning: it''s likely that similar coatings will be applied to many other stones in the near future. It''s important that sellers be aware of this problem and disclose any such treatments.

 

[Harriet]

Rick,

On the subject of coating, what is the current status of the Andesine controversy?

 

[Richard M.]

No coating on them that I''ve heard.

The "status" depends on who you read and believe. The major study being done by Dr. Rossman at Caltech has not been released and there''s no indication of when it will be. Meanwhile various individuals have reported findings from their own studies that have generated a lot of heat but not a lot of real light or agreement as far as I can tell. There''s a new study by French gemologists that indicates some sort of copper diffusion process but it''s pretty non-specific.

I prefer to wait for Dr. Rossman to release his findings before I even speculate publicly. I have theories based on a lot of input from various sources but there are many gaps and inconsistencies that need to be reconciled. I don''t think it pays to rush to judgment.

Richard M.

 

[LD]

Thank you all for your input. It''s alarming that people can be duped in this way - the pieces I mentioned above were being valued when the coating was discovered and the buyer was totally unaware as the items had been bought from a company with a very good reputation for Tanzanite. I hadn''t realised that it was the smaller stones in particular that may be treated which is interesting.

Richard thank you also for your very level headed and sensible approach to the Andesine debate. So many have rushed to judgement and I agree that waiting for findings is the way forward.