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.
Joined: Tue Mar 13, 2007 11:12 am Posts: 483 Location: Ohio and 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.
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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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