I thought there were ways to tell synthetic from natural? Surely DeBeers were particularly interested in discrediting Soviet diamonds and if they could find proof that those were indeed synthetic, they would have used it?
Not sure, I read an article some years ago that said as much. I expect you could identify natural diamonds by impurities and subtle imperfections in the cut, but I don't know how you could conclusively prove a too-perfect diamond was synthetic.
According to this article[0] it is possible, but it's not like there's one 100% accurate method - but a skilled gemologist should be able to identify a synthetic diamond:
Yes, it's possible with a high degree of confidence to distinguish natural from synthetic diamonds and for synthetics, to determine which method (HPHT or CVD) was used to make them.
The IIDGR [1] company makes a series of devices (DiamondSure, DiamondView and DiamondPlus) that will indicate whether a diamond is a natural (and if so, of what type), or flag it for further characterization. One system will flag type IIa naturals for further analysis, as they resemble the best of CVD synthetic diamonds. Microscopy + (IR, fluorescence, and photoluminescence) spectroscopy distinguish a stone's origin to high confidence. Even though the best CVD stones have far lower impurities than the best naturals, they have internal strain patterns (optical birefringence) that can be diagnostic.
Most jewelers don't have these machines, but they are available as a service.
Faceted CVD stones have been seen up to 5 carats [2] and 10 carat stones made by HPHT are known [3]
I recall watching a documentary where the reporters got diamond merchants to test some diamonds. Many of the synthetics were easily spotted but one - from a new technique or something - was only spotted because it was "too pure".
The testers a typical jeweler or diamond merchant might use only identify between diamond, cubic zirconia or moissanite. They do not identify origin of a diamond.
The testers that can identify a diamond's origin are quite expensive and usually only found at major gemological labs.
All synthetic white diamonds are "Type IIa" (no or trace amounts of nitrogen) while only 1-2% of mined diamonds are IIa. 97% of mined diamonds are "Type Ia" (clusters of nitrogen). It is possible that is what they were referring to about purity, but the amount of nitrogen is not a definitive indicator of origin.
Perhaps the same documentary, but a while back I saw something where the latest techniques were easy to spot for being too good. But then they showed a new technique being developed that was able to inject natural seeming imperfections. The show claimed that this was the impetus for DeBeers laser etching their mark on diamonds as they had no other way of detecting the difference.
This was a while ago though so I'd imagine the cat & mouse game has evolved for both sides.
That's how all synthetics are identified... natural diamonds all contain impurities from the material they were formed near/in.
It's sort of funny in a way... impure diamonds are worth more than pure diamonds... but then again, none of them would be worth much at all if DeBeers didn't control the release into the market (diamonds are not rare at all, and therefore only valuable due to artificial scarcity).
