Post subject: How can you tell if a ruby/sapphire has been heated?
Posted: Tue Nov 06, 2007 12:48 am
Established Member
Joined: Sat Oct 20, 2007 4:53 pm Posts: 48
it is my understanding that it is fairly easy to identify irradiated stones with the proper equipment, but how do you determine if corrundum has been heat treated?
Joined: Mon Oct 17, 2005 2:39 pm Posts: 3528 Location: San Francisco Bay Area, CA
One method that is used is microscopic examination. There are often inclusions in corundum that undergo characteristic changes when the stone has been subjected to heat treatment.
I have just completed a course on i.d. of treated and synthetic stones. My book gives amongst other i.d. criteria for untreated corundum (it does not distinguish between blue and other colors) the following:
"Complete Fe spectrum of lines at 451.5, 460 & 470 is proof of natural (or heat treated) origin. A weak 451.5 line has been found in certain Verneuil and flux (Chatham) corundums.
'Natural heat treated corundum (normal type)' amongst several criteria in the book it gives"expanded/melted crystals, partly disolved silk etc., color banding tends to be more fuzzy". This is from my book.
ursula
Joined: Tue Mar 13, 2007 11:12 am Posts: 484 Location: Chiang Rai Thailand
Thanks Ursula for that info.
Great reading Doos, appreciate the link. A Raman is on my wish list.
So far in my observations I have found almost no great looking unheated corundum, even in the rough markets of mining areas. This could mean that it is as scarce as hens teeth or simply that I was not waving enough cash around, perhaps a combo of the two.
Almost all the rough I saw that was unheated looked like heat would be a good idea if you wanted to be able to sell the finished product.
All the unheated faceted stones I have run across that were certainly unheated looked second rate.
Easy to see why heat is basically accepted.
That sapphire is awesome. I love the purple but I admit I'm a sucker for non-standard/typical colors in a stone and I think I have just about every color in a sapphire except that one. Unheated too. Nice choice for an avatar. I can't decide what my avatar should be and I don't want to create any infighting and accusations of "special" treatment within my gemstone collection. They are very sensitive to these things.
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