Diamonds are among the most beautiful — and most counterfeited — gemstones in the world. With advances in lab-grown diamonds and imitation stones like cubic zirconia and moissanite, it’s now harder than ever for the average person to tell what’s real.
The good news? You don’t need a full gemmology lab to make an educated guess. There are simple at-home tests that can help you spot the difference between a genuine diamond and a convincing fake — and just as importantly, you’ll learn when to get expert verification.
At Blackwell Jewellers, we work with both natural and lab-grown diamonds, each tested and certified for quality and authenticity. Whether you’re checking a new purchase, inheriting a family ring, or simply curious about what’s in your jewellery box, understanding how to identify real diamonds is a valuable skill.
In this guide, we’ll share six simple tests you can try at home, plus professional insights from our in-house jewellers. You’ll learn how to check for sparkle, durability, heat resistance, and more — and when it’s time to let a professional gemologist take a closer look.
“Real or not? Here’s how to tell the difference.”
The Sparkle Test — Fire & Brilliance
A real diamond has a sparkle like nothing else. It’s what jewellers call fire — the rainbow flashes of colour — and brilliance — the white, intense light that seems to come from deep within the stone. While other gems may glitter, only a genuine diamond reflects light in this uniquely powerful way.
To test this at home, find a spot with good natural light. Hold your diamond up to the light or place it under a lamp and move it slowly from side to side. A real diamond will scatter light into both rainbow colours (fire) and sharp white reflections (brilliance). Fake stones, like cubic zirconia, usually produce too much rainbow light and not enough clean white sparkle — they appear “too perfect,” almost glassy.
You can also try comparing your stone to another piece you know is real. Diamonds have a crisp, sharp reflection, while imitations often look cloudy or dull under the same lighting.
It’s worth noting that lab-grown diamonds pass this test too — because they are real diamonds, with identical crystal structures to mined ones. The sparkle and brilliance are indistinguishable from natural stones, which is one reason they’re becoming so popular with modern buyers.
At Blackwell Jewellers, we use professional-grade tools to measure a diamond’s light performance, fire, and symmetry. It’s how we ensure every diamond — natural or lab-grown — meets the highest brilliance standards.
“Real brilliance can’t be faked — diamonds reflect both fire and light from within.”
The Fog Test — Breathing on the Stone
One of the easiest and most revealing ways to tell if a diamond is real is something you can do in seconds — the fog test. It’s a quick, science-based way to check how your stone reacts to temperature and moisture.
Hold the diamond close to your mouth and gently breathe on it, as if you were fogging up a mirror. A thin layer of condensation will appear on the surface. Now watch how fast it disappears.
If it’s a real diamond, the fog will vanish almost instantly — usually in less than a second. Diamonds are incredible heat conductors, meaning they disperse warmth (and moisture) very quickly. The surface won’t stay misted for long.
If it’s a fake diamond like cubic zirconia, moissanite, or glass, the fog will linger for a few seconds longer before clearing. These materials don’t conduct heat nearly as efficiently, which makes this one of the simplest ways to spot the difference.
It’s important to note that lab-grown diamonds will behave exactly like mined diamonds in this test. They share the same molecular structure and physical properties, so they disperse heat in the same way. That’s why even experienced jewellers rely on professional instruments to distinguish between the two.
At Blackwell Jewellers, we use advanced diamond testers that measure thermal and electrical conductivity to confirm authenticity — giving you 100% certainty every time.
“A real diamond won’t fog up for long — its heat conductivity clears mist instantly.”
The Water Drop Test — Density & Buoyancy
Another simple way to tell if your diamond might be real is through density — how heavy it feels for its size. Diamonds are extremely dense gemstones, and this property affects how they behave in water.
To try this test, fill a glass with clean water and gently drop your loose stone (not a ring setting) into it. A real diamond will sink straight to the bottom almost immediately. Its density is higher than most imitation stones, so it won’t float or linger halfway down.
A fake diamond, such as cubic zirconia or glass, often sinks more slowly — or may even hover slightly before settling. Moissanite, a common diamond alternative, will usually sink as well, so this test alone can’t confirm authenticity — but it’s a helpful indicator when used alongside others like the sparkle and fog tests.
It’s important to handle your stone carefully when performing this test. Avoid dropping it into hard surfaces or deep containers where it could chip or become lost. Always retrieve it gently using soft plastic tweezers or by tipping the water into a sieve over a clean surface.
While this test is quick and easy, it’s not foolproof. At Blackwell Jewellers, we use advanced gemological instruments that go far beyond density — including refractive index and conductivity analysis — to confirm whether a diamond is genuine or synthetic.
“A real diamond sinks instantly — its density makes it heavier than it looks.”
The Heat Test — Toughness & Thermal Conductivity
Diamonds are famous for their strength, and one of the best ways to prove that is through heat resistance. A genuine diamond can handle extreme temperature changes without cracking, making this one of the most dramatic — yet revealing — tests you can try.
To perform a simple version of the heat test, hold the stone carefully with tweezers and heat it using a lighter for about 30–40 seconds. Then immediately drop it into cold water.
A real diamond will remain completely unaffected — no damage, no cracks, and no change in appearance. Diamonds are formed under intense heat and pressure deep within the Earth, so this sudden temperature change is nothing compared to their natural creation conditions.
However, if the stone shatters or becomes cloudy, it’s not a real diamond. Materials like glass, quartz, or cubic zirconia will expand and contract under heat, causing fractures when cooled suddenly.
Of course, this method should be done very carefully and only with loose stones. Never heat jewellery that’s already set, as the metal can warp or the mount may weaken.
Both lab-grown and mined diamonds will pass this test equally, since they share identical chemical and physical structures. That’s why the only way to know for certain is to have your diamond professionally tested using a thermal conductivity tester or gemological microscope.
“Diamonds don’t fear fire — their strength comes from it.”
The Professional Test — Certification & Expertise
While home tests can give helpful clues, the only way to be absolutely certain that your diamond is real — and understand its full quality — is through professional testing and certification. This is where jewellers like Blackwell Jewellers come in.
A certified jeweller uses specialist tools that measure thermal conductivity, refractive index, and electrical resistance, all of which are impossible to judge accurately without professional equipment. These readings confirm not only whether a diamond is real, but also whether it’s natural or lab-grown — both genuine, but with different origins and market values.
We also examine the diamond’s cut, clarity, colour, and carat weight (the “4Cs”), which determine its beauty and value. Every test is carried out under controlled lighting and magnification to detect tiny details invisible to the naked eye — things like inclusions, symmetry, and polish quality.
Once authenticated, a genuine diamond can be accompanied by a certification report from leading gemological institutions such as the GIA (Gemological Institute of America) or IGI (International Gemological Institute). These certificates act as a passport for your stone — proof of its authenticity, grade, and value, trusted by jewellers and insurers worldwide.
At Blackwell Jewellers, all our natural and lab-grown diamonds are verified and accompanied by full certification. Whether you’re buying an engagement ring, assessing an heirloom, or simply curious about what you own, we offer professional diamond testing in-store — quick, accurate, and completely transparent.
“Certification is confidence — the only way to know your diamond’s true story.”
Know What You’re Wearing — Confidence Is Clarity
Diamonds may be timeless, but understanding them takes more than a quick glance. Whether it’s a gift, an heirloom, or an investment, knowing if your diamond is real gives you peace of mind — and appreciation for what makes it so special.
With today’s technology, lab-grown diamonds are visually and chemically identical to mined ones. That means even experts rely on advanced tools and certification to confirm origin. But for you, the real goal isn’t just testing — it’s understanding.
At Blackwell Jewellers, we believe knowledge transforms ownership. When you understand your diamond — how it’s made, how it’s valued, and what makes it sparkle — you gain a deeper connection to it.
“Clarity isn’t just a diamond grade — it’s peace of mind.”
