How to tell if gem is real from a glance

[Joel21]

Is there a way to tell if a gem is real just from a glance or is it impossible to see the difference between a real diamond and a good fake just by looking at them?

 

[Bron357]

I can pick a CZ from a diamond at a glance. Mainly because CZ have a particular whiteness to them that is rarely seen in a natural diamond. Other modern imitations are much harder. Moissanite and Amora gem are both very diamond like in appearance and unlike CZ tend to be set in higher quality settings adding to the realism. With a loupe you can see the double refraction aspect of these Silicon Carbide created gems but in a modest size they can fool even a jeweller who just "glances" and doesn't test. These Moissanite and Amora gems do test as Diamond on a thermal tester as they have a very Similiar refractive index to diamond, so that can be a trap for the unwary. CZ just tests as "glass" so it's pretty obvious to anyone using a thermal tester. With coloured gems ie sapphire it gets even more difficult as many synthetics are made from the exact same material as their natural gem counterparts. You may need laboratory testing to confirm if such gems are natural or man made. It is best to buy from a reputable source to ensure you are getting a genuine natural gem rather than a modern, fancy and marvellous man made replica.

 

[lambskin]

Without a loupe and just by a glance IMHO, the smaller the CZ and the more classic setting the harder to tell. I was at Ross today and saw a beautiful CZ band set in sterling that looked pretty convincing. CZ round cuts are harder to tell at a glance than a fancy cut. From an untrained eye at a party or other social gathering it would pass.

 

[ChristineRose]

I disagree.

Someone who knows what to look for can tell a Moissanite from a diamond at a glance.

All other things equal, no one can (probably) tell CZs from diamonds, but there are a lot of extenuating circumstances.

CZs are almost always icy white, but sometimes they are deliberately made warmer. Diamonds are usually not icy white.

CZs are always internally flawless--again, unless someone has made one with inclusions to fool you.

If it's badly cut--as in wonky angles--it's likely a cheap CZ or an antique diamond.

It it's badly cut--as in cut for weight, not brilliance--it's likely a diamond.

Of course someone could cut a CZ any way they pleased, just to fool you.

A CZ is much more likely to be chipped or scratched. But there are chipped diamonds and unchipped CZs.

So let's imagine the hypothetical case where you have a CZ and a diamond of identical size, cut, color, clarity, and condition. Can you tell them apart?

Side by side, quite possibly. The CZ has less brilliance. But a proper test like this would require twenty or so identical pairs of stones, and they would not be side by side (that's more than a glance) and would have to test many people who claim to be to be able to tell a CZ at a glance.

There was a thread a while ago where Pricescopers were asked if they could tell a CZ from a diamond, and lots of people said they could, but when they said why, they all said things like the quality of the setting, an enormous rock being worn by a person who doesn't look rich, etc. In other words, they were all really saying that they could not tell a diamond from a CZ.

Simpler versions of my test have indicated that no, no one can reliably tell a CZ from a diamond at a glance. The "read-through" test is probably the most reliable easy test, but even it's not 100% and it requires more than a glance. The fog test is too dependent on external conditions to be of much use.

 

[Tophat1]

I can't. I have a gorgeous diamond (WF ACA) Ring and a well cut CZ ring that I use for travel. Side by side, I can tell the diamond is better cut but that's the only difference I can see.

 

[blueMA]

I could absolutely tell the difference between CZs and Diamonds.
More easily, there's no mistaking a good quality diamond.

 

[Barrett]

I can tell usually. Not with Paraiba tourmaline though