How to tell Diamonds from Cubic Zirconium

February 27, 2020 - Jewelry & Luxury Items

How can you tell diamonds from simulants?

In the 1970s the diamond market was flooded with what’s known as Synthetic Cubic Zirconium, or CZ. Cubic Zirconium is the most prevalent synthetic diamond. It is made in a lab instead of being formed by the Earth so it’s much less rare & valuable than a real diamond.

When Cubic Zirconium first appeared on the market it was relatively expensive. As laboratories found more sophisticated and cheaper ways to make the simulants—CZ became cheaper. Now the proliferation of the ‘fake diamond’ has made the simulant almost laughably cheaper compared with real diamonds.

A single carat polished CZ stone can be retailed at $20 while it’s diamond equivalent can be sold at $1,500! (This, of course, depends on diamond’s grades along the 4 Cs: carat, color, cut, clarity). Still, the disparity in value between Cubic Zirconium and authentic, certified diamonds is astounding!

First Line of Defense: PawnGuru

If you’re looking to do any business in diamonds, we recommend using PawnGuru.

This is your first line of defense!

With PawnGuru, you can make a free listing to buy, sell, or pawn a diamond or jewelry. There’s no obligation to do any business so you can just use PawnGuru as a tool to gauge the value of your diamond. Your listing is sent to every pawnshop in your local area. Minutes later, jewelers will email you their offers.

Using PawnGuru’s community-reviewed system, you can sift through non-reputable shops to find an honest dealer you really want to work with. Once you’ve found a reputable dealer, you’ll need to educate yourself on diamond grading and certification. There are a few tests you can do at home to find out how to tell diamonds from Cubic Zirconium. Figuring out if you’ve got the real deal will save you time you would otherwise waste traveling to a pawnshop to find out your jewelry is worth next to nothing!

How to Tell Diamonds From Cubic Zirconium at Home!

There are a few ways to tell the difference between a true diamond and CZ right there at home. For these tests, you will need to have a loose diamond for accuracy. If your diamond is still fastened to a ring, necklace, or any other jewelry, your best bet is to visit a pawnshop with a Gemological Institute of America Certification (GIA). A GIA certified shop’s diamond appraiser has the necessary tools and instruments to appraise your diamond while it’s still encased in jewelry.

If you do have a loose gemstone there are a few things you can do on your own to immediately know whether you’ve got a diamond, or not!

1. The Weight Test

You will need a small scale that can measure milligrams and then convert to carats—the standard industry unit diamonds are measured. It’s simple. 100 milligrams equals a half carat. You can use weight to differentiate between CZ and a diamond pretty easily.

Diamonds weigh about 1.7 times less than Cubic Zirconium. So, if you have a rounded diamond that is 6.5 mm this will be approximately a single carat in weight, or 200 mg. The same size CZ stone will weigh 140 milligrams more, or .7 carats. Meaning, the CZ stone will weigh a total of 1.7 carats (340 mg) compared to a 1-carat diamond (200 mg).

If you don’t have a scale at home, don’t worry there are still more tests you can run yourself!

2. The Fog Test

This test is even simpler than the weight test and will take seconds. You don’t need any equipment, just a basic understanding of the properties of diamonds and Cubic Zirconium: diamonds are efficient heat conductors while CZ has less thermal conductivity.

Simply breath on your gemstone as you would to fog up a mirror. If it’s a real diamond the fog will dissipate immediately. If the fogginess lingers on the surface of the gem, then this is CZ!

3. The Reading Test

This is another easy home test you can use to tell diamonds from Cubic Zirconium. All you have to do is take your loose stone and lay it upside with the ‘table’ of the stone flush against the print of a newspaper or magazine. This allows you to measure the potential diamond’s refractivity. Diamonds have a more complex relationship with light and will bend light as it enters the stone whereas CZ does not.

This means if you can read the words you have Cubic Zirconium if you cannot, you got a real diamond!

If you’re still in doubt of your diamond’s authenticity, use PawnGuru as a liaison between you and a GIA certified diamond appraiser!

David Stiebel
David Stiebel

David Stiebel is one of the cofounders of PawnGuru. David was educated at MIT, where he studied Math. He subsequently worked at Bain as a data scientist before starting PawnGuru in 2015. He started PawnGuru to build a better tool for pawn shops and consumers to connect.

More Articles


Comments are now disabled