How to tell if a Diamond is real or fake?

How to tell the difference between and Diamond and a Cubic Zirconia

The inspiration for this post came from a random google search on how to tell if a diamond is real, as I just wondered what kind of information was out there and after reading quite a few blog post, articles and watching YouTube videos from so called ‘experts’, I realised that the quality of advice out there was really and I mean REALLY bad. So I sat down a wrote this guide, just for you lovely people!

Firstly, what not to do!

As I mentioned above, there is some really bad advice out there and most of the things I read or watched included these so called home tests you can do to check if your diamond is real, honestly don’t waste your time doing these and you can read below why they are completely useless:

  1. The Water Test: Real Diamonds sink in water whereas fake diamonds float – without getting too technical, nearly all gemstones will sink when placed in water as nearly all gemstones are denser than water so will sink to the bottom. I have tested this one out myself just due to pure curiosity and stones such as quartz, which is much less dense than a diamond will still sink in a glass of water.
  2. Blacklight Test: Diamonds only fluoresce blue when put under ultraviolet light – diamonds can fluoresce in a variety of different colours but blue is the most common but not all diamonds will fluorescence
  3. Visual Test: Checking the sparkle of the stone – there are a few flaws to this test, the first being that unless you know what the sparkle of a diamond should look like, how are you going to now if yours is sparkly enough? or too sparkly? Plus some diamond cuts such as an Emerald Cut does not sparkle anywhere near as much as a Round Brilliant cut.

These tests appeared in quite a few different places and it seemed like most of the results were copied and pasted from each other.

What is a fake diamond?

There isn’t really anything that is a fake diamond as the gemstones that look like diamonds are real gemstones, they just aren’t diamonds and in the world of gemmology we call these gems simulants as they are made to simulate the appearance of a real diamond. There are two main simulants used to imitate diamonds and they are:

  1. Cubic Zirconia or CZ – first produced in the 1970’s, the CZ is the most commonly used diamond simulant in the world due to being inexpensive and doing a pretty good job of looking like a diamond.
  2. Synthetic Moissanite – first sold to the public in 1998, synthetic moissanites were marketed as the world’s best diamond simulant due to the fact that they would pass as a diamond using handheld thermal testers. Significantly more expensive than CZ’s and are a little more difficult to spot.

So how can you tell what is a real diamond?

You really have three options when it comes to telling if you have a real diamond and I will cover all three below.

Option Number 1: Take it to a jewellery professional

Honestly, the best way to tell if you have a real diamond or not is to take it someone who knows what they are talking about. I know it sounds like I am stating the obvious but it is the best way to know. The best people to take it to are jewellery valuers, gemmologists or diamond graders and these can be found in independent jewellers and pawnbrokers, specialist auction houses, gem labs or they may have their own business. These people, such as myself have spent a lot of time and money learning how to tell gemstones apart as it is a specialized skill and if it was easy, anyone would be doing it. If you can’t find one of the listed above, then an experienced jeweller should be able to tell the difference.

Option Number 2 – Use an Electronic Tester

If you still want to check the stone yourself, then the best option is to use an electronic tester and you really want to use a dual tester that checks for diamonds and synthetic moissanite as this will give you a more accurate result. You can buy separate diamond and synthetic moissanite testers, which work out a bit cheaper but you will still need to use both as individually they do have limitations. Using an electronic tester is pretty easy and only takes around a minute to do.

Simply place the probe at a 90° to the table (the big facet on the top of the stone) press down slightly so that the probe makes a good connection with the stone and wait for a result. A dual tester will tell you whether it is a diamond, synthetic moissanite and in some cases if it is a sapphire, CZ don’t cause any reaction with the testerm so if you get not response then it is a CZ or possible another colourless gemstone.

As you can see, it is pretty easy to get a result from using an electronic tester but it should be noted that these testers can get things wrong and should be used as an indication of what the stone is, not as a definitive test.

What are the limitations of individual diamond and moissanite testers?

  • Diamond Tester – diamond testers check to see if the stone is thermally conductive but as both diamond and synthetic moissanite are thermally conductive, using this tester will only narrow down your possible choices to two gemstones
  • Synthetic Moissanite Tester – these check the electrical conductivity of the gemstone. With the exception of only one very rare type of diamond, all diamonds are electrically inert, whereas synthetic moissanite are electrically conductive. These testers are design to just identify synthetic moissanite and won’t give any indication as to whether the stone is a diamond, cz or another simulant.

Option Number 3 – Looking at the stone

This is the way the professionals do it, now I am not saying by doing the tests and observations I talk about below will make you a professional but by taking to time to observe the stone and look for certain characteristics, you can learn to differentiate between diamonds, CZ’s and synthetic moissanites. I have listed the basic equipment you will need to do these tests below:

  • Lined Paper
  • A jewellery cleaning cloth
  • A Jewellers Loupe with 10x Magnification
  • A pair of diamond tweezers (if the stone is loose)
  • A darkened room
  • A single light source, such as a desk lamp

Before we start….

Always make sure the stone is clean before doing any of these tests as dirt on the surface of the stone can give you incorrect results. If the stone is loose, a simple wipe over with a cleaning cloth will work, if the stone is set then putting the piece in an ultrasonic cleaner will give it a good clean, if you do not have an ultrasonic cleaner, a soft toothbrush and warm soapy water will do the job, just make sure you wash all the soapy water off after cleaning it.

Test Number 1: The Read Through Test

Now I am sure you are wondering why I have included a piece of lined paper as a piece of equipment, well there is one really easy test you can do but it does come with two limitations 1) this can only be done with loose stones and 2) it can only be done with round brilliant cut stones. So if you have a loose round brilliant cut stone, you can do what is called the ‘read through’ test and all you do is place the stone on the line of the piece of paper and see if you can see it through the stone.

Read through test for diamond and cubic zirconia

As you can see in the image above, you cannot see the line through the stone on the left, this is because round brilliant diamonds are cut in a way that they have what is called total internal reflection and this causes any light or visuals entering through the table of the stone to be reflected within the stone and they go back out through the table. If the diamond is not cut to ideal proportions, you may be able to see some of the line through the stone but most of it will be reflected back out of the stone. As you can see with the stone on the right, you can still quite clearly see the line through the stone due to the fact it has been cut to look like a diamond, rather than to produce total internal reflection. BUT and this is a big but, this test will only narrow down whether the stone is a diamond or a synthetic moissanite.

Test Number 2: Look at the finish of the girdle

As with test number 1, this test is only really useful when it comes to round stones but it is a really useful and easy test to do. First off, what is the girdle? The girdle is the perimeter of the stone where the crown (top) and pavillion (bottom) of the stone meet. When trying to identify if the stone is a diamond or cubic zirconia, examining the finish of the girdle can help you, you may be able to do this with your naked eye or you may need to use your 10x loupe.

The two images above are what you may see when looking at the girdle condition of a polished stone. The image on the left is what is called bruted and this is only seen on diamonds and it has a frosted and satin appearance to it, where as the image on the right is what is called grounding and this is where they grind the girdle of the stone and this can be seen by many small vertical lines running along the girdle, this is only done to cubic zirconias. Unfortunately they can finish girdles in other ways, such as polishing or faceting them, if this is the case then other tests will need to be done. What I like about this test is that it is quick and easy to do and can be done if the stone is in a claw setting. With any stones that have straight edges such as princess, emerald or baguette cut, the girdles will always be polished or faceted.

Test Number 3: Look at the surface condition of the stone

This is the thing I teach people to do the most when trying to decide if the stone is a diamond or cz as it something that it easy to do and only requires basic equipment (loupe and tweezers if the stone is loose). Diamonds are the hardest natural material known to man and sit at the very top of the MOHS hardness scale at 10, as they are so hard, it takes time and effort to polish them so that they have that lustre that everyone expects when they see a diamond. This means that the finish is usually done to a very high standard and all the facet edges are sharp and precise, all the points meet up with each other and there are no easily visible polishing marks on any of the facets and this can be seen in the image on the left below. Where as the image on the left, the facets don’t look as precise, sharp or well finished, this is because CZ’s are cheap and it is not cost effective for the stonecutters to make sure every stone is perfect, as long as it looks good then it will do. Often on CZ’s, you will see misaligned facets and often extra facet edges to compensate for the misalignment. There is also a higher chance of polishing marks being visible on the facet faces.

You may also see more damage on a CZ than you would a diamond as they are softer, only scoring 8.5 on the MOHS scale. This means that they are more likely to get chipped or abraded along the facet edges and faces than a diamond. Now I am not saying that diamonds can’t be chipped or abraded, but there is far more chance of it happening with a CZ than a diamond. The facet edges may also be a little more rounded than a diamond as being softer means they don’t take such a good final polish. So of you see that the stone is poorly cut and has damage at a few points around the stone, this is a good indication that the stone is a CZ.

I would like to note here that Swarovski now do a range of Cubic Zirconia that are cut to a really good standard but they have been very kind and laser inscribed Swarovski across the table to help us identify them.

Test Number 4: Look for inclusions

This is something that gets overlooked by many jewellery professionals but it really is a simple thing to do. Using you jewellers loupe and tongs if the stone is loose, have a look through the table of the stone (the large facet on the top of the stone) and see if you can see any inclusions in the stone, I have included a link below to the GIA’s list of inclusions as there are quite a few:

GIA list of inclusions

Now you may not see any inclusions as it does take some practise and experience to be able to easily spot them, especially in higher clarity diamonds but if you do quickly and easily spot an inclusion in the stone, that is similar to those on the GIA list, then there is a good chance that you have a diamond as the majority of cubic zirconias have really good clarity due to the way they are made. There is one inclusion that you can see in synthetic moissanite and the are called growth tubes (image below) and form when the gemstone is made, these are less common in new stones but were seen in earlier ones.

Test Number 5: Check for doubling

The tests above are mainly for checking whether or not you have a Diamond or a CZ but how to you tell the difference between a Diamond and a Synthetic Moissanite? The easiest way is to check for doubling.

Check for what? Doubling is an optical effect known as double refraction that is seen in some gemstones and it is where the light splits into two when it enters the stone from the air, due to the stone having two optic axis whereas Diamond only has one and by only having a single optic axis, diamonds are singly refractive. There are many different gemstones that have two or more optic axis but it is only visible in a handful of gemstones and synthetic moissanite is one of them.

How to see doubling in a synthetic moissanite

To do this test you will need a 10x loupe and your Diamond tweezers, if the stone is loose. Pick the stone up in the tweezers and look through the kite facets (shown in the above image) at around a 45° angle, it is always worth adjusting the angle slightly to make sure that you do not miss it. Look through the stone and look at the pavilion facets on the opposite side of the stone. If you can clearly make out single facet edges as seen in the picture on the left below, then you are more than likely looking at a diamond. If however you cannot clearly see that facet edges, picture on the right below then you are looking at a synthetic moissanite. You may see two lines for each facet edge in some stones, in other it may appear very hazy and it is difficult to differentiate what is a facet edge and what isn’t.

What I really like about this test is that you can do this test with a loose or set stone, some settings do make this a little more challenging but it is still possible and you do not need any specialist equipment. It may not be easy to do this test at first but once you know what you are looking for, it does become a lot easier to do.

What about Synthetic Diamonds?

Synthetic diamonds are becoming more and more common in the world of jewellery, but how can you tell if your diamond is natural or synthetic?

Unfortunately telling the two apart requires far more advanced equipment that costs thousands of pounds and there are not simple visual tests to tell which one is which but advancements are being made and the equipment is becoming cheaper and more accessible, so more and more jewellers and pawnbrokers will have equipment that can indicate the origin of your diamond.


I know that the tests above are far more in depth than most of the other guides out there but what makes this one different is that I teach people how to do this and I know that with a bit of time and practise, differentiating between gemstones does become easier and may even give the bug to want to learn more about diamonds and gemstones!