7 Ways to Spot Fake Diamonds

7 Ways to Spot Fake Diamonds

8 Ways to Spot Fake Diamonds

7 Ways to Spot Fake Diamonds

Have you ever been suspicious that a loose diamond you bought wasn’t real? or wondered whether your diamond jewellery was genuine? If the stone came with a certificate from the GIA or AGS you can rest assured that it’s legit. However if the diamond was a gift or an inheritance and you don’t have the certificate you’re right to wonder.

If you’ve got a stone you’re in doubt about, here are 7 ways to check its authenticity.


Should you try the scratch test?

People used to think that the “scratch test” was the easiest way to test a diamond. The test is to simply scratch the loose stone against a mirror. The idea is that if the stone is hard enough to scratch the mirror, it’s probably a diamond.

In terms of the Mohs scale however this test proves inaccurate. The Mohs scale is a scientific measurement of mineral hardness. Glass is rated a 5.5 and diamonds the hardest mineral are a 10. So, genuine diamonds will scratch a mirror. On the other hand so will quartz (7), moissanite (9.25) and cubic zirconia (8). Moissanite and cubic zirconia engagement rings are almost as hard as their diamond counterparts.

Most well-made synthetic diamonds will seem authentic if you only use the scratch test.

Here are some other tests with more reliable results.

1. It’s a little too perfect: The Magnification Test

The Magnification Test

What you need:

A magnifying glass with 10X magnification or higher

A diamond that you know is genuine

Your questionable stone

How it works:

First look at your questionable stone under the magnifying glass. Then look at the genuine diamond and compare the differences. The genuine diamond will have some internal or external flaws, known as inclusions. If the other stone is cubic zirconia or moissanite, it will have no internal flaws and probably no external flaws either.

That’s because real diamonds are natural rocks that were formed in the earth, while cubic zirconia and moissanite are grown in labs. They’re not subject to all the environmental pressures that diamonds get while forming so they don’t have those telltale quirks that identify a real diamond.


If you don’t have a real diamond to compare your loose stone to you should head to your local jeweller.

If your questionable stone happens to be legit and has a clarity grade of Internally Flawless or Flawless, you won’t see any internal flaws. These are the rarest and most expensive diamond clarity grades though and it’s unlikely a diamond of such high quality isn’t certified unless its an heirloom piece.

2. It retains heat: The Fog Test

The Fog Test

What you need:


The questionable stone

How it works:

Go to a relatively cool location and blow hot air on the stone. You’re trying to surround the stone with warm moist air. Since a real diamond doesn’t retain heat well your breath won’t create a fog on its surface. But a piece of moissanite will get fogged up quickly just like your mirror, sunglasses or cell phone screen.

3. It doesn’t glow: The Black Light Test

The Black Light Test

What you need:

A strong UV light

The stone

How it works:

Hold the stone under the UV light and see if the colour seems to change at all. If the stone emits a bluish glow it is most likely a real diamond.


Because of the way fluorescence in real diamonds works this test isn’t definitive. Since some real diamonds don’t have any fluorescence you wouldn’t see a blue glow even if it was real.

So, if the stone doesn’t emit a blue glow or glows a different color under the UV light you can try another one of these tests at home. To get the most definitive answer you should take it into a professional jeweller.

UV light

4. You can see right through it: The Newspaper Test

The Newspaper Test

What you need:

A newspaper

The stone in question

How it works:

Place the stone on top of the newspaper and see if you can read the words on the page through it.
A real diamond of decent quality will refract light so intensely that you can’t see through it. On the other hand cubic zirconia is more transparent and you’ll be able to see right through it.


This test is less reliable if the stone is relatively small (less than a half-carat) or is set in a piece of jewellery which can obstruct your view.

5. It can’t take the heat: The Candle/Lighter Test

The Candle/Lighter Test

What you need:

A lighter or candle flame

A glass of very cold water

A pair of tweezers to hold the stone with

The stone in question (loose — don’t do this if it’s in a piece of jewellery!)

How it works:

Holding the loose stone with the tweezers, heat it up over the lighter or candle flame for about 30 – 45 seconds. Then drop it immediately into the icy water. A real loose diamond will not react to this extreme temperature change (they’re made of extremely strong material). However, many fake diamonds – including those made of glass, cubic zirconia or quartz – will break or shatter during this test.


If your stone survives this test, congratulations! But be prepared to clean off any residual ash from the flame afterward. The quickest way is to soak it in a solution of warm water and toothpaste for at least 3 minutes, then gently scrub it clean with a toothbrush.! And don’t forget to rinse!

6. It floats: The Water Test

The Water Test

What you need:

A glass of water

The loose stone

How it works:

Simply drop the loose stone into the water. Loose diamonds are so dense they should sink to the bottom when dropped in a glass of water. Many diamond fakes – glass and quartz included – will float or not sink as quickly because they’re less dense.


This test is not foolproof. Large pieces of cubic zirconia and moissanite can sink fairly quickly if they’re heavy enough even though they’re not as dense as a diamond.

7. It resists electricity: The Conductivity Test


What you need:

You’re going to have to leave the house for this one. Take your stone to a local jeweller.

How it works:

Something that not too many people know about diamonds is that they resist electricity. Testing a loose stone for electric conductivity is especially helpful if you aren’t sure whether your stone is a diamond or moissanite. Moissanite (if it is made well) can be extremely difficult to tell apart from a genuine diamond, having the same level of thermal conductivity. However, one relatively simple way to tell the difference is that moissanite will conduct electricity while a natural diamond will not.

With the rise of moissanite in today’s diamond market, the majority of jewellers have an electricity testing tool on hand to determine the real from the lab-created.

8. Use a diamond tester

Use a diamond tester

There are plenty of diamond and gem testers on the market to The SmartPro Gem-Eye is a good example of a diamond tester as it has been developed to distinguish between diamond and other simulants by way of thermal conductivity.

Diamonds, with their exceptional heat conductivity properties are unlike any other simulant, and are therefore not easily replicable. The diamond tester is now equipped with a color stone estimator display to assist the user in distinguishing popular colored gemstones form each other.

The SmartPro Gem-Eye I consists of two linked thermometers: one, which is heated electronically, while the other is cooled by the gemstone being tested. The difference in temperature creates an electrical output, which is then amplified and displayed on an analog dial.