I've tested a piece in our lab as well and it jumped right out at me as the backside was peeling like a norwegian after a week in Jamaica.
Supposedly there is some reaction to hydrogen peroxide as well but I've not confirmed that.
As for sapphire, I've not seen any but don't doubt it would be floating around somewhere. Currently looking on one new synthetic sapphire that is grown using cobalt as the chromophore. Looks a lot like cobalt spinel and has almost the same spectra.
Joined: Mon Feb 02, 2009 8:15 pm Posts: 112 Location: London, UK
I've got some silly questions to ask, I have been thinking about them for a while, I just don't understand why people would coat stones, I am thinking more on the financial side, (hehe.. being as an accountant, I always think of $$, if no profit made, why would people bother doing it?)
Is it easier and cheaper to coat stones than heat treatment?
Do they heat treated the tanzanite first before coating?
Joined: Tue Nov 01, 2005 7:30 am Posts: 203 Location: London
Maybe Peter can pipe up about what he saw later.
Sorry for the delay … Having seen the lab alerts about cobalt coating of tanzanite, it made me wonder if some of those blue sapphires with 'too good to be true' colour had undergone the same treatment. I started to look at the sapphires with a chelsea filter and more than a few were showing up pink/red which would indicate chromium or cobalt, neither of which are found in natural blue sapphires. This reaction was sometimes seen in whole parcels sometimes seen in part of a parcel.
I asked around but was met with the usual wall of silence. I do not know how they coat them, no one would tell me.
Maybe Vincent has seen some come in the lab for testing?
I just don't understand why people would coat stones, I am thinking more on the financial side, (hehe.. being as an accountant, I always think of $$, if no profit made, why would people bother doing it?)
I have never re-polished a coated sapphire but would expect to find pretty weak colour under the coating if I did. Some weaker coloured blue sapphires can be picked up at pretty cheap prices. If they coat them with a wonderful rich blue colour they could in theory be sold at higher prices by unscrupulous dealers. It would only be by removing the coating that the true colour would be revealed.
I wanted to buy a couple of these stones on my last buying trip for dissection purposes. I wanted to buy them cheap but unfortunately they were asking way too high a price to make it worth while. I’m not rich enough to go around sawing up expensive stones …!
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