I have a Paradscha sapphire which is 7ct. I have taken it to be appraised to see if it is natural or not. All tests say that it was indeed a natural gem, except for one. This was a test where a special light was used. The gem glowed, indicating that it was actually man-made. Could you please explain this test to me, is it creditable?

Answer:

Padparadscha sapphire is a rare light orangy-yellow to orange form or corundum, and it would be very unusual if your 7 carat stone was genuine; this color has been synthesized for generations, and a natural stone of this size would be very rare indeed. You're right to want to check it out, though, because if you have the real thing it could be quite valuable.

I suspect that whoever was examining your stone was looking for fluorescence. Natural orange sapphire does fluoresce, though (strong orange-red in LW), so I may be wrong--can you ask the jeweler to explain the test?

In a gem of this size natural inclusions would almost always be present, so if your stone is flawless that would suggest synthetic. A true synthetic has the same optical properties as the natural gem, so refractive index testing will be inconclusive, but synthetic corundum produced by the verneuil method (the most common one) often show fine, curved bands of color under the microscope, called "curved striae" and if you see this, it's positive proof of synthetic origin. Curved striae are often hard to resolve in orange synthetic sapphire, though, so if you DON'T see them, it doesn't mean you have a natural gem.

I'd recommend a second opinion on your stone, possibly from either the Gemological Institute of America's Gem Trade Lab or American Gemological Laboratories.. (Hanna).