Post subject: Is heating possible with red to violet spinel
Posted: Sun Nov 03, 2013 4:06 am
New to the Forum or The Quiet Type
Joined: Thu Oct 31, 2013 3:15 am Posts: 8
Hi,
Does anybody have any information to share regarding spinel heat treatment. I have few red to violet dark spinels. is there any recipe to lighten its colour. i will post a image in the next post. I tried my best to find something. but I could not find anything special. I could hear few incidents like violet spinel getting lightened after treating. which was wrongly identified as a sapphire. I hope he should have treated it to remove blue to make it pink. but i doubt that will this work with spinel. if the answer is yes to which extent is it successful. if anybody can clarify i will be grateful.
viewtopic.php?f=24&t=3445&p=161001 Unless something has changed in the mean time, generally spinel is not known to improve with heating or really any other treatment.
Post subject: Re: Is heating possible with red to violet spinel
Posted: Wed Nov 20, 2013 3:56 pm
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Joined: Thu Dec 13, 2007 3:42 pm Posts: 4091 Location: the Netherlands
Scarodactyl wrote:
http://www.gemologyonline.com/Forum/phpBB2/viewtopic.php?f=24&t=3445&p=161001 Unless something has changed in the mean time, generally spinel is not known to improve with heating or really any other treatment.
Yes it does, both clarity and color can be positively affected by relatively low heat. It even says so in a link posted in the thread you link to
That's really interesting. The link to that PDF in the thread itself didn't work so I was going by what others had said there (and what I've read elsewhere, though it must have been outdated info).
Post subject: Re: Is heating possible with red to violet spinel
Posted: Wed Nov 20, 2013 5:37 pm
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Joined: Thu Dec 13, 2007 3:42 pm Posts: 4091 Location: the Netherlands
What is remarkable is that Chris doesn't encounter much heated stuff in his lab. All this is done in oxidizing atmospheres at temperatures one can easily achieve.
Could it be cause sleepy spinels are good sellers?
It is easily detected by Raman so should not cause much problem. There are also some spinels that are affected negatively colourwise, or so I have been told anyway. That might be a reason to be restrictive with heating which then will be less common. Just a theory.
Post subject: Re: Is heating possible with red to violet spinel
Posted: Tue Sep 16, 2014 8:19 pm
Gold Member
Joined: Mon May 26, 2014 9:42 pm Posts: 1033
Weird - I read the paper you pointed to and it seemed to say that "this treatment was not being performed to improve color, since their experiments showed either little to no color modification or a less desirable color resulted from the heating. However, they did find that the transparency of certain spinels could be significantly improved by heating at temperatures between approximately 950C and 1150C"
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