How to Know if a Diamond is Real or Fake: 11 Tests

Some key characteristics make a diamond a diamond, so it’s a good idea to be aware of these before conducting any tests.

• Refractive index: 2.417
• Dispersion: 0.044
• Singly refractive
• Specific Gravity: 3.52
• Hardness: 10 on the Mohs scale (hardest on Earth so that a hammer won't shatter it)
• Thermal conductivity: Highest of any substance

Note: Each test used to assess how genuine a diamond is will test each of the characteristics above. It’s important to note that the tests are the same for lab-grown and mined diamonds. 

Although it’s recommended that you get your gem checked out by a diamond expert who uses specialised equipment and can say for certain whether you’re dealing with a real diamond, there are a few ways to check if a diamond is real at home. Just remember to do any of these tests with patience and care for your stone.

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The first and most common test to identify if a diamond is real is the water test. Start by filling a regular glass about three-quarters of the way with water, then gently drop the diamond into the glass — a real diamond should sink to the bottom. If it floats or remains near the surface, it’s most likely a fake. Note: for this test, you must use a loose diamond, not one set in metal. 

Another simple test you can try at home is the fog test. Hold the diamond or ring between your fingers and breathe gently on it. The stone should fog up briefly, but because diamonds conduct heat efficiently, the fog should clear almost instantly. If the fog lingers for several seconds, it’s likely not a real diamond.

If your diamond is set in a ring, one of the easiest ways to identify whether it’s real is to look at the type of setting and mount that’s used. Because of its value, genuine diamonds are typically set in high-quality metals for their protection and durability. Look closely at the metal for markings that indicate the material, like gold or platinum.

Inspect the inside of the ring band for stamps like 10K, 14K, and 18K, which represent the gold used—or the number 750 (meaning 75% pure gold). When looking at platinum rings, you’ll find markings like PT and Plat or the number 950, which indicates the ring is 95% platinum. If you spot a C.Z. stamp or engraving, the gem is cubic zirconia, meaning it’s not a real diamond.

>> Also read: Diamond Quality and Grades

In addition to the water, fog, and engraving tests, you can also identify if a diamond is real through light. Genuine diamonds reflect both white and coloured light with exceptional brilliance, creating its beloved sparkle. The quality of this brilliance — the reflection of white light — and fire (coloured light) is a key indicator of its authenticity.

How to test a diamond this way: place it under a lamp and observe how the light reflects off the stone. You should see flashes of bright white light as well as colourful light reflections. In a real diamond, you should see both its incredible brilliance and fire. Simulated diamonds, however, typically don’t refract light as well, although Moissanite is the exception; the gemstone usually has more fire because they have a higher dispersion and refractive index than a diamond. Because of the subtleties in testing, we always recommend getting your stone professionally assessed.

One of the easiest tests to do is the dot test. Start by placing a piece of white paper on a flat surface and drawing a little dot with a pen. Next, lay the gem onto the dot with the flat side down. Through the pointed side of the diamond, the one facing towards you, look down onto the paper. 

See if you can notice the dot — if you can, it’s most likely fake; if the dot is obscured, it’s likely real. This is because a diamond refracts light in multiple directions, causing light to scatter rather than travel in a straight line. As a result, you won’t be able to see the dot through a real diamond. You can also try this with a newspaper or magazine, checking if the text appears through the stone (the read-through test).

Once widely used, the scratch test was meant to determine the hardness of a gemstone’s mineral. All it took was scraping the loose gem along a mirror to see if it would scratch the mirror or the stone. 

However, while a diamond is created with very strong materials, even fake diamonds like moissanite and cubic zirconia are rather durable and scratch-resistant, too. Because of that, it’s better to use another test form to see if you have a real diamond.

There’s one more method you can do at home when you’re figuring out how to test for a real diamond. Just like a diamond expert might do, you can use a tool to determine the gem’s thermal conductivity. As diamonds are great heat conductors, the diamond should disperse heat rapidly after it’s warmed. If it doesn’t, then it’s most likely not real. 

Note: Synthetic moissanite stones often disperse heat, just like real diamonds. This test, therefore, becomes inconclusive with this particular gem.

While there are several tests you can do on your own to see if your diamond is real or not, the most reliable results come from a professional gemologist. These trained experts, often with a Graduate Gemologist (GG) degree, have access to advanced tools and tests to tell a diamond’s authenticity. 

Using a jeweller’s loupe (a magnifying glass), they can closely examine the stone for blemishes and imperfections, which are common in real diamonds. Fake diamonds, on the other hand, are often flawless. To get conclusive answers, they might even use a 1200x magnification microscope or perform an x-ray of the stone.

Additionally, gemologists usually have a fine-tuned scale to measure the weight of the stone. This way, they can notice small differences in weight. Real diamonds are typically lighter than synthetic stones like cubic zirconia, so by comparing the weight of the diamond to a similarly sized fake stone, they can spot any discrepancies. This is usually done using the Specific Gravity test, whereby the density of a gemstone is compared to the density of the water.

Experts also use electricity conductivity testing. This test measures how well the stone conducts electricity — diamonds conduct electricity far better than most other gemstones, including moissanite. 

Note: It’s worth having your diamond reviewed by an expert, as they can run these tests to see if you’ve got a real stone. Even when it’s unclear to the naked eye, it helps to know, especially for resale and insurance purposes.

As we said before, there are very strict guidelines for stating that a diamond is real. Anything other than the real gem is labelled as a diamond simulant, one that mimics the appearance of a diamond but is chemically and optically different. Some common simulants are moissanite, white sapphire, cubic zirconia, and white topaz. 

Fyne Tip: We always recommend getting your gem inspected by a jeweller with the tools to test its authenticity.

Moissanite is a synthetic material made of a highly rare substance found in meteorite fragments and a very common ‘dupe’ for diamonds. This is because it’s difficult to spot the differences between moissanite and natural diamonds with the naked eye, often requiring a professional to determine for sure.

When looking into how to check if a diamond is real, you’ll learn that moissanite has a higher refractive index and brilliance than mined and lab grown diamonds, showing greater fire and coloured flashes. An electricity conductivity test is the likeliest test to spot these differences and provide a definitive answer.

It’s important to note that synthetic diamonds (those grown in a lab) shouldn't be confused with simulated diamonds (gems that mimic diamonds, such as cubic zirconia and moissanite). Lab grown diamonds are not fake diamonds; they have the exact same chemical and optical properties as earth mined diamonds — the only difference is that they are created in a lab. On the other hand, simulated diamonds have entirely different properties from real diamonds, which are noticeable to the naked eye.

Lab grown diamonds are a more accessible, affordable, and ethical option for acquiring a beautiful gem. As they share the same chemical and molecular properties, they shine and sparkle just like the mined versions. The real difference can only be seen by a diamond expert, who’ll run conductivity tests and view the diamond under high magnification. It’s important to note that all the imitation tests are the same for both lab diamonds and earth mined because they have the same properties, such as specific gravity, refractive index, thermal conductivity, and Mohs scale.

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Other common diamond imitations include: 

• Cubic Zirconia. This one is relatively easy to distinguish from real diamonds after a few diamond identification tests. For example, the sparkle test will show apparent less sparkle and fire in a cubic zirconia. However, they typically also weigh more, lack inclusions, and reflect orange-tinted light. 
• White Sapphire. These stones also don’t have the same sparkle as a diamond does, often looking somewhat cloudy and blurred in colour. 
• White Topaz. Its softness is the most apparent feature that differentiates this stone from a diamond. Diamonds are hard substances and can’t be scratched by other minerals. However, topaz can.

>> Also read: Types of Diamonds Explained