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 Post subject: Detecting topaz coatings
PostPosted: Fri Jun 16, 2006 11:20 am 
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The pavilion coatings used for many of the treated topaz varieties can often be easily detected. Some of these stones are pretty much sight IDs but one should always confirm.

Below is a mystic topaz variety. AT 30X and using only reflected light the coating on the pavilion of this stone is easily detected. There is even a difference in surface luster between the crown and pavilion facets.


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PostPosted: Fri Jun 16, 2006 11:44 am 
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Another view in reflected light at a different angle. The colors are representative of what you see reflected face up through the crown.


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PostPosted: Fri Jun 16, 2006 12:01 pm 
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Good info, JB.

There's now a new/old one to be alert for. I recently received a pitch from an Asian cutter for a series of topaz doublets in nearly every color under the sun. The first clue should be colors that don't -- or rarely -- occur in natural topaz.

ROM


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PostPosted: Fri Jun 16, 2006 12:17 pm 
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Have you looked at any of the coated "believable" colors like pink, salmon, blue to see if you get a similar effect?


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PostPosted: Fri Jun 16, 2006 12:40 pm 
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Rom, the doublets will be something to watch for. Usually doublets are pretty easily detectable with a close visual inspection. Of course strong vibrant colors also set off the red flag.

Barbra, I haven't examined the type you speak of. I would like to, just to bust them. If it's some kind of diffusion as opposed to surface enhancement, the ID may be more difficult. Once again, unnatural color for that specific gem is a red flag. If it's pavillion only treatment, I would look for subtle difference in surface luster, if nothing is detectable coating wise with magnification, it's time to move on to immersion or other more definitive tests.


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PostPosted: Fri Jun 16, 2006 12:47 pm 
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JB wrote:
If it's some kind of diffusion as opposed to surface enhancement, the ID may be more difficult.


Diffused topazes are out there in deep Ceylon sapphire blue, teal, deep green and, I think, bi-colored green/blue. Next to corundum I think white topaz is the "most-treated" gem mineral around.

ROM


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PostPosted: Fri Jun 16, 2006 3:42 pm 
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ROM wrote:
JB wrote:
If it's some kind of diffusion as opposed to surface enhancement, the ID may be more difficult.


Diffused topazes are out there in deep Ceylon sapphire blue, teal, deep green and, I think, bi-colored green/blue. Next to corundum I think white topaz is the "most-treated" gem mineral around.

ROM
We sold a very large "red" coated topaz on our ebay store(disclosed of course) and we found it by closely observing the girdle as well as the regular RI...i mean how often do you see a topaz that's red rivals fine ruby??? :roll:

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PostPosted: Fri Jun 16, 2006 4:44 pm 
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Darren,

Do you recall what your observations were when you examined it through the girdle?


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PostPosted: Fri Jun 16, 2006 5:42 pm 
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JB wrote:
Darren,

Do you recall what your observations were when you examined it through the girdle?
Chipping of the coating in locations around the prongs...it was a fairly large stone and was a bit loose so i figure movement caused that peeling/chipping of the coating...the peeling/chipping of the coatings looks like a clear/colorless area surrounded by color.

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PostPosted: Fri Jun 16, 2006 6:24 pm 
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Thanx,

If anyone owns any of these non-mystic, pavillion coated topaz, could you check them out for us and report your observations? My instinct tells me that lighting and magnification will detect these coatings without any destructive tests. You may have to crank the mag up a little or try various lighting techniques.

If you can take pics that would be good also.


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PostPosted: Sat Jun 17, 2006 12:57 pm 
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As an after thought, another observation I made on this coated stone was, the applied coating appeared to migrate away from the facet edges.
You will probably be able to depict that in the images above. This resulted in a noticeable difference of luster between the edge areas and the center of the facets, in reflected light.

Even if the topaz has a predominate hue of just pink or red or salmon or whatever colors are available with this type of treatment, it may be possible to observe this kind of discrepancy.


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PostPosted: Thu Nov 16, 2006 11:57 pm 
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JB wrote:
Thanx,

If anyone owns any of these non-mystic, pavillion coated topaz, could you check them out for us and report your observations? My instinct tells me that lighting and magnification will detect these coatings without any destructive tests. You may have to crank the mag up a little or try various lighting techniques.


This an old thread, but I am surprised to see that many people describe the topaz as "pavilion coated" when the coated topaz I have are all crown coated. Some of the "peach salmon" and "golden orange" colored "Imperial topaz" being sold on eBay appears to be coated too, though the sellers feign ignorance. Turn the stone upside down, and you have a pretty clear pavilion.

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PostPosted: Fri Nov 17, 2006 12:40 am 
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If you have information the rest of us don't, why not do some research of your own and report your findings to enlighten us?

The stones described as coated on the pavilion only are manufactured in the U.S. by azotic thin-film technology. The main manufacturer coats stones on the pavilion only for 2 reasons: so it won't be damaged in daily wear, and so the stone will give a genuine topaz R.I. when tested -- a little sneaky, that last one!

There's another U.S. manufacturer that does much the same except some of their stones are diffused, not coated. Diffusion stones include bicolors, Ceylon sapphire blues, and greens.

It doesn't require much imagination to suppose topaz coating is being done in many places with many different approaches. My guess is it's going on in Bangkok, China, Brazil, etc. I've seen "Mystic topaz" offered by Chinese dealers and some of the pink and red topaz I see being offered at very low prices appears to be coming from South America. So dig into it and let us know what you find out.

Rick Martin


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PostPosted: Fri Nov 17, 2006 12:25 pm 
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ROM,

The only thing I can tell you at the moment is that the crown-coated topaz all came from Thailand. I'll give the stones some further study and see what happens. I have some Thai "Imperial topaz" that fades to white in the sunlight. The "peach salmon" colors, if they are indeed coated, should, of course, show no fading. That would be one simple test. Scratching is of course another simple option.

Kingfish

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