Book Appointment
Marylebone, London

How to tell if a diamond is fake

Examining a diamond under a loupe

Table of contents

Primary Item (H2)

If you’re buying from Ingle & Rhode then this isn't something you'll need to worry about, but if you choose to buy a diamond elsewhere, knowing how to spot a fake diamond might prove very valuable to you! So read on to learn how to tell if a diamond is fake!

Can you tell a fake diamond from a real one with the naked eye?

When looking at an apparent diamond with the naked eye, the average person is not likely to be able to tell if it's real or not. The stone is likely to be fairly small, making it difficult to observe any features that might indicate if it’s real or fake.

If you’re familiar with gemstone brilliance, you may be able to have an idea if your stone is a real diamond. A diamond’s brilliance is a subtle sparkle. Both moissanite and cubic zirconia have higher refractive indexes than diamond. The result is a bright fire that differs subtly from the classic brilliance of a diamond.

Keep in mind that other colourless diamond simulants can have a brilliance closer to that of a diamond. Both white zircon and white topaz have similar light performance.

Diamond authenticity certificate

A diamond certificate from an independent laboratory can indicate your stone is likely to be a real diamond. You should observe the certified diamond carefully and look under magnification for the report number etched onto the diamond's girdle. If the report number is verified on both the diamond’s girdle and the certificate, it’s very likely to be a real diamond.

Though a certificate can give you a good idea of its authenticity, you shouldn’t hastily buy any old certified diamond, as some diamond grading labs are more reputable and have stricter grading standards than others. 

Testing if your diamond is fake at home

There are some tests you can perform at home to check if your diamond is real. Here are some of the most popular:

1. Magnifying glass

Many people keep a magnifying glass in their homes. You may also need a pair of tweezers to hold your diamond in place if you have difficulty holding your loose or mounted diamond.

hand white glass isolated tool looking lens circle magnifying glass focus glasses look zoom search find optical magnifier magnification loupe magnifying magnify vision care enlarge 1034246

A magnifying glass can assist you in determining if your diamond is authentic by revealing laser inscriptions. Many certified diamonds have their diamond grading report number and the name of the lab that certified it inscribed on the girdle. A diamond certificate is a very good indication that your diamond is a real diamond.

However, it is possible to obtain a fake diamond with a fake report number, which is one of the reasons that the major grading labs allow you to verify your report online. But beware, some dishonest sellers copy real grading reports that can be verified and apply them to fake diamonds.

2. Water method

This simple test only requires a glass of water and your diamond, but note it can only be used on a loose diamond. Diamonds that have been mounted onto ring settings cannot be tested in this way.

Fill your glass and drop your diamond in. If it floats to the top, it’s not a real diamond! Diamonds have a density level of 3.50 – 3.53 g/cm3. That means diamonds are around 3x more dense than water itself, which is why a true diamond will sink to the bottom of the glass. 

Note that diamonds are not the only white gemstone that will sink when dropped in water. Diamond simulants such as cubic zirconia and moissanite will sink to the bottom of the glass too. 

3. Heat method

The heat test is also best performed on a loose diamond, and should only be performed with extreme caution. Please note also that your diamond (or fake diamond) may well need cleaning after this test.

4367029329 cbbbe4d507 c
Credit: Tom Raftery (Creative Commons Licence)

Firstly, you’ll need a source of heat, such as a candle flame. You should also have a pair of tweezers and a glass of cold water close by. 

Make sure your loose diamond is being held securely by your tweezers in one hand. Bring the diamond close to the candle flame for around 30 seconds. 

If it’s a fake diamond or diamond imitation, it may shatter. However, there are other white gemstones that can withstand heat. White sapphire and cubic zirconia will shatter if brought to heat for an extended length of time. A white topaz gem’s colour is altered when brought to high heat. Moissanite and white zircon will withstand the heat like a diamond. 

Stones may need to be cleaned after performing this test. After soaking them in warm water for a few minutes, you should be able to remove any soot and ash from the surface of the stone with a soft toothbrush. 

4. Type of setting

This is one of the few tests for diamonds already mounted into a setting. Most jewellers would only mount real diamonds in solid precious metals like gold and platinum.

If your piece of jewellery has been hallmarked then it is made of solid precious metal, but if it is not stamped, it’s likely to be plated. Gold-plated jewellery has a very thin layer of real gold plated over another base metal. If it’s gold plated over sterling silver, you will see it referred to as gold vermeil.

A reputable jeweller will not set a real diamond in a gold-plated setting, so if your jewellery is gold-plated, then it is unlikely that the diamond is real. However, beware because the opposite is not necessarily true - if your jewellery is solid gold or platinum, this does not guarantee the gemstone is a diamond. It is not uncommon to see moissanite for example set in solid gold. 

5. Fog method

You won’t require any special equipment for this test, and it can be done with a mounted or loose stone. You will just need good eyesight to view your stone’s table facet (the flat top surface of the stone). 

If you’re performing this test with a loose stone, you’ll want to make sure you’re in a safe place if the diamond should slip through your grasp. Tweezers may make this easier for some. 

Hold the stone close to your lips and breathe on it as if you were trying to fog up a window. If you find it difficult for the table of your stone to fog up this is a good sign. Diamonds do not retain heat well, making them difficult to fog. 

How does a professional tell the difference between a fake diamond and a real one?

The most common method used by professionals to prove the authenticity of a diamond to a customer is by using thermal conductivity. In simple terms, most would know this as a diamond tester. The metal tip is placed at an angle on the table of the stone. It can tell you if your stone is a diamond, but it might not tell you what stone it is if it’s not a real diamond.

Some diamond testers have the option to test moissanite. You should be careful with diamond testers because they often mistakenly detect real diamonds as moissanite because of user error.


It can be quite challenging to distinguish between a real diamond and a fake one. Fortunately, there are some ways to test if a diamond is real or not. Some tests can be performed at home, but none of these is completely conclusive, and for a definitive test you will require the assistance of a jeweller.

David Rhode
Together with Tim Ingle, David created Ingle & Rhode to offer a better alternative to the traditional luxury brands. Since 2007, we’ve provided our customers with genuinely ethical engagement rings, wedding rings and fine jewellery – free from conflict diamonds, dirty gold and child labour. With more than 16 years experience in the jewellery industry, David has deep expertise in diamonds, gemstones and jewellery design and manufacturing.