Identifying fake corundum

[jcharles]

I recently purchased two synthetic corundum stones off of eBay, one sapphire and one ruby. They are perfect stones. And when I say perfect, I mean perfect. Under 45X magnification on a microscope, I can''t see anything to indicate they''re created stones. Not a bubble, band or speck visible anywhere. This, of course, led me to wonder whether they were corundum at all, or simply colored cubic zirconia.

They are both doubly refractive. But I gather CZ are double refractive as well, so this doesn''t help. The ruby fluoresces under UV, quite strongly in fact. The sapphire appears to have no fluorescence whatsoever. From my understanding, both of these traits would seem to indicate that they are, in fact, what they were sold as—synthetic ruby and sapphire. But is there any such thing as a "perfect" synthetic?

Sadly, I have no access to a spectrometer or anything, and having them tested by a gemologist would surely cost more than I paid for the stones.

Does anyone have any thoughts on whether my fakes are real or not?

 

[jcharles]

I contacted the seller. This is what he says:

"These are a newer proprietary process developed in Singapore. The supplier will not give out any details, but my gemologist friend thinks it may be a new flux based technology with much more controlled crystallization. Sorry, but that is about all I know about these."

 

[Richard Sherwood]

If they are both truly doubly refractive, then a host of singly refractive simulants and imitations are eliminated (including cz, which is singly refractive).

You can determine if the red stone is corundum (ruby) with the following procedure:

In a dark room, hold the table of the stone up to your eye, almost touching your eyelashes, and look at a small concentrated point of light through the stone (such as a penlight, turned at an angle to reduce the size of the light image).

Spectral images of the light will appear through the stone at the periphery of your field of vision. You might have to raise or lower the stone to bring them into view.

If the images consist of red and blue only, the stone is ruby. Ruby absorbs all the visible spectrum except for red and blue.

If the stone is ruby and flawless, it is most definitely synthetic. Actually, if you had a higer power scope you would probably resolve some characteristic synthetic inclusions or features which you're not picking up with the 45x scope. Different types of lighting, such as diffused lighting, or pinpoint fiber optic lighting would help in this regards as well.

If the red stone is corundum, chances are the blue is as well, especially if it is doubly refractive. There's not that many doubly refractive blue stones with the color of sapphire around that aren't corundum. Glass is your closest color match, but that is very obviously singly refractive.

 

[jcharles]

Sure enough, looking through the ruby I see only blue and red. Nice tip!

 

[leggs]

I am interested in also buyng from this seller on ebay. Would you share his sellers id or send a link to what you bought.
Thanks