Mindat.org Conference 2014 Madagascar 28 May 2014 - 13 June 2014
Welcome to the GemologyOnline.com Forum
A non-profit Forum for the exchange of gemological ideas
It is currently Sat Apr 19, 2014 5:26 am

All times are UTC - 4 hours




Post new topic Reply to topic  [ 8 posts ] 
Author Message
 Post subject: Cobalt treatment of Tanzanite and Blue Sapphire
PostPosted: Tue Apr 07, 2009 4:47 pm 
Offline
Moderator

Joined: Sun Oct 16, 2005 12:42 pm
Posts: 2846
Location: Ho Chi Minh City, Vietnam
Anyone have any information on this?


Share on FacebookShare on Twitter
Top
 Profile  
 
 Post subject:
PostPosted: Tue Apr 07, 2009 6:49 pm 
Offline
Valued Contributor

Joined: Sun Mar 08, 2009 2:16 pm
Posts: 255
Nuck,

Here is the story from AGTA lab
http://www.agta-gtc.org/coated-tanzanite.htm

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.

Bear


Share on FacebookShare on Twitter
Top
 Profile  
 
 Post subject:
PostPosted: Tue Apr 07, 2009 7:35 pm 
Offline
Moderator

Joined: Sun Oct 16, 2005 12:42 pm
Posts: 2846
Location: Ho Chi Minh City, Vietnam
Ah, I hadn't realized it was a coating that Peter was talking about for the Tanzanite, ok. I suppose that maybe for sapphires, it was the same thing. Maybe Peter can pipe up about what he saw later.

How does the cobalt doped synthetic sapphire look to the naked eye compared to the usual synthetics?

Quote:
as the backside was peeling like a norwegian after a week in Jamaica.


I had to explain to my husband why I was sitting here literally laughing out loud after that one. Then we both were :lol: You're a witty guy, :)


Share on FacebookShare on Twitter
Top
 Profile  
 
 Post subject:
PostPosted: Wed Apr 08, 2009 11:24 am 
Offline
Valued Contributor

Joined: Sun Mar 08, 2009 2:16 pm
Posts: 255
africanuck wrote:
How does the cobalt doped synthetic sapphire look to the naked eye compared to the usual synthetics?


The syn cobalt corundum looks virtually identical to that of the cobalt syn spinels. A bright almost neon blue.:smt026
____
bear


Share on FacebookShare on Twitter
Top
 Profile  
 
 Post subject:
PostPosted: Wed Apr 08, 2009 1:33 pm 
Offline
Moderator

Joined: Sun Oct 16, 2005 12:42 pm
Posts: 2846
Location: Ho Chi Minh City, Vietnam
Thanks Bear


Share on FacebookShare on Twitter
Top
 Profile  
 
 Post subject:
PostPosted: Thu Apr 09, 2009 2:23 am 
Offline
Valued Contributor
User avatar

Joined: Wed Oct 22, 2008 1:48 am
Posts: 120
Location: Germany
There are a couple more links about the joint AGL/AGTA work on the new tanzanite treatment here.

There's also a recent G&G article about coated tanzanites:
McClure and Shen (2008) Coated tanzanite. Gems & Gemology 44, 142-147.


Share on FacebookShare on Twitter
Top
 Profile  
 
 Post subject:
PostPosted: Thu Apr 09, 2009 9:36 am 
Offline
Valued Contributor
User avatar

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?

Phyllis


Share on FacebookShare on Twitter
Top
 Profile  
 
 Post subject:
PostPosted: Fri Apr 10, 2009 11:59 am 
Offline
Valued Contributor
User avatar

Joined: Tue Nov 01, 2005 7:30 am
Posts: 203
Location: London
africanuck wrote:
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?


wypwong wrote:
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 …! :?
P.

_________________
www.apsara.co.uk


Share on FacebookShare on Twitter
Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 8 posts ] 

All times are UTC - 4 hours


Who is online

Users browsing this forum: No registered users and 0 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

Search for:
Jump to:  
Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group
Gemology Style ported to phpBB3 by Christian Bullock