How to Identify Real Diamonds

Use the fog test. Place the stone in front of your mouth and exhale onto it, just like you would with a mirror. If it fogs up for a few seconds, it’s not a diamond — a real diamond disperses the heat from your breath instantly and won’t fog up easily. Even if you exhale and observe closely, a real diamond will remain clear.

• For easier comparison, place a real diamond next to it and exhale on both. You’ll notice the real diamond stays clear, while the fake one will fog up. With continuous breathing, a layer of fog will start to form on the fake stone, while the real one remains sparkling and transparent.

Examine the structure and setting. Genuine diamonds are not set in cheap metal frames. A setting marked with stamps indicating gold or platinum (10K, 14K, 18K, 585, 750, 900, 950, PT, Plat) is a good sign, while a “C.Z.” mark suggests the stone is likely not a diamond.

Use a professional jeweler's loupe. You can purchase one from a gem store. Natural diamonds often have minor imperfections visible under magnification. Look for tiny mineral inclusions or slight color variations, which indicate a real, albeit imperfect, diamond.

• Zirconium stones (which often pass most tests) lack these imperfections because they are created in controlled environments rather than formed naturally. A stone that appears too perfect is often not natural.
• However, a real diamond can also be flawless. Do not rely solely on imperfections to determine authenticity. It’s just one factor among many.
• Note that lab-grown diamonds lack natural imperfections due to their controlled production environment. Lab-created diamonds are chemically, physically, and optically identical (sometimes even superior) to mined diamonds. This has caused significant concern in the mined diamond industry, as they fear investing heavily in stones that may not be “natural.” Lab-grown diamonds are “real” but not “natural.”

Observe the stone's refraction. Diamonds bend and refract light intensely, creating a dazzling sparkle. Other stones like glass or quartz do not sparkle as much due to lower refractive properties. The brilliance is inherent to the stone and cannot be altered by cutting. By carefully observing refraction, you can determine if the stone is real. Here are some methods:

• Newspaper test: Place the stone face down on a newspaper. If you can read the text through the stone or see blurred black marks, it’s not a diamond. A real diamond refracts light so intensely that nothing is visible through it. (Exceptions exist: poorly cut diamonds may still allow some visibility.)
• Dot test: Draw a small dot on a white paper and place the stone over it. If you see a circular reflection in the stone, it’s not a diamond. A real diamond will not allow the dot to be visible.

Check the reflections. A real diamond typically reflects shades of gray. Look straight down from the top of the stone. If you see rainbow reflections, it’s likely a low-quality or fake diamond.

• Additionally, examine the sparkle. A real diamond will shine far more brilliantly than glass or quartz of the same size. You may want to carry a piece of glass or quartz for comparison.
• Do not confuse sparkle with reflection. Sparkle refers to the brightness or intensity of light refracted by the stone’s facets, while reflection refers to the colors of light refracted. Look for “bright” light, not multicolored light.
• There’s a stone that sparkles even more than diamonds: moissanite. This gem is so similar to diamonds that even experts struggle to tell them apart. To differentiate without special tools, hold the stone close to your eye and shine a penlight through it. If you see rainbow flashes, it’s a sign of double refraction, a characteristic of moissanite that diamonds lack.

Drop the stone into a glass of water and see if it sinks to the bottom. Due to its dense structure, a real diamond will sink. Fake diamonds will either float on the surface or remain suspended in the water.

Heat the stone and test its durability. Heat the suspected stone with a lighter for 30 seconds, then immediately drop it into a glass of cold water. Rapid expansion and contraction will overwhelm weaker materials like glass or quartz, causing them to crack internally. A real diamond, being extremely hard, will remain unharmed.

Request a thermal conductivity test. The tightly packed crystal structure of diamonds allows them to disperse heat quickly, making real diamonds difficult to heat. This test takes about 30 seconds and is often free. The advantage is that it does not damage the stone.

• This test works on the same principle as the DIY “break the stone” method above. Instead of risking damage, the probe measures how long the stone retains heat.
• For a more professional assessment, consult a local jeweler.

Request a combined diamond/moissanite tester. Many gem shops have specialized equipment that can quickly distinguish between real diamonds and imitations.

• A traditional thermal test cannot differentiate between moissanite and diamonds. Ensure the test uses a “thermal conductivity” meter, not a “temperature” meter.
• If you frequently test diamonds at home, consider purchasing a gem tester available online or at diamond specialty stores.

Use a microscope. Place the stone under a microscope with the top face of the diamond facing downward. Gently move the diamond back and forth using tweezers. If you notice a faint orange light along the edges, it might be cubic zirconia (C.Z.). In some cases, it could be a real diamond with imperfections filled using cubic zirconia.

• For the clearest view, use an electron microscope with 1200x magnification.

Diamonds are highly sensitive to weight. Diamonds can be easily distinguished by their weight difference; cubic zirconia is about 55% heavier than a diamond of the same shape and size. For this comparison, you’ll need a highly sensitive scale that measures in carats or grains.

• To perform this test accurately, you’ll need a real diamond of the same shape and size for comparison. Without a reference, determining authenticity becomes challenging.

Test the diamond under ultraviolet (UV) light. Under UV or black light, most (but not all) diamonds fluoresce blue. If your stone emits a blue glow, it’s likely real. However, the absence of blue light doesn’t prove it’s fake; some diamonds don’t fluoresce under UV light. A faint green, yellow, or gray glow might indicate moissanite.

• While UV testing can narrow down possibilities, avoid relying solely on it to confirm authenticity. As mentioned earlier, some diamonds fluoresce, while others don’t. Fake diamonds can also be treated to glow under UV light, so nothing is certain.

Conduct an X-ray test. Diamonds have a “radiopaque” molecular structure, making them invisible on X-ray images. Glass, cubic zirconia, and crystal, however, appear clearly on X-rays due to their slightly “non-radiopaque” properties.

• To X-ray your diamond, take it to a professional diamond testing lab or negotiate with a local X-ray facility.

Identify lab-created diamonds. Lab-grown or synthetic diamonds are “real” but not “natural.” While they cost a fraction of natural diamonds, both share similar chemical properties. Distinguishing between natural and synthetic diamonds requires professional processes using advanced equipment and techniques, such as detecting higher uniformity (near-perfect structure) typical of lab-created gems and identifying specific non-carbon elements in the crystal. Lab-grown diamonds are priced lower due to successful PR campaigns by the natural diamond industry, which emphasizes the rarity and value of “natural” over “synthetic.” If you’re buying, selling, or insuring gemstones, knowing their origin—natural or lab-created—is crucial.

Recognize moissanite. It’s challenging to differentiate moissanite from diamonds. While they look similar, moissanite has double refraction, making it sparkle more intensely than diamonds, though this requires close observation. Place a real diamond next to the stone in question and shine light through both. If the stone emits more colorful and broader light bands, it’s likely moissanite.

• Diamonds and moissanite have similar thermal conductivity. Using only a diamond tester might yield a “diamond” result for moissanite. For accurate identification, professionals use combined diamond/moissanite testers.

Identify white sapphire. White sapphire is another stone that resembles diamonds and can confuse non-experts. However, it’s softer than diamonds. Mineral hardness is determined by scratch resistance. Diamonds are among the hardest minerals, easily scratching other stones without damage. If your stone shows scratches, it might be white sapphire or another softer gem.

Spot white jade. Many assume “jade” refers only to green stones, but it comes in various colors. White jade, or transparent jade, is often used as a diamond substitute. However, it lacks the sharpness and sparkle of real diamonds. If your stone appears dull or lacks brilliance, it might be white jade.

Identify cubic zirconia (commonly called C.Z.). Cubic zirconia is a synthetic stone that closely resembles diamonds. The easiest way to spot it is by its color reflection. C.Z. often reflects an orange hue. While cubic zirconia is “clear,” natural diamonds usually have tiny mineral inclusions and slight imperfections.

• When light focuses on cubic zirconia, it emits colorful spectral bands, whereas real diamonds sparkle with colorless reflections.
• Another common test involves rubbing the stone against glass. Many believe if the stone scratches glass without damage, it’s a diamond. However, high-quality cubic zirconia can also scratch glass, making this test unreliable.

Find a reputable diamond appraiser in your area. Most diamond retailers hire their own gemologists and appraisers, but many consumers feel more confident seeking an independent third-party appraisal from a gemologist specializing in diamond evaluation. If you’re investing in gemstones or curious about a diamond you own, you’ll want an objective and accurate assessment.

• Gemstone appraisal involves two basic steps: identifying and evaluating the stone, then assigning a value. When choosing an independent appraiser, look for someone with a college degree, graduation from a national gemological institute, and certification from an organization not directly involved in diamond trading. This ensures the appraiser is qualified.
• When having a diamond appraised, ensure the process is done in your presence rather than sending it elsewhere.

Ask the right questions. Beyond determining if the diamond is real, an appraiser can clarify doubts about the stone’s quality. This is especially important if you’re buying or inheriting a gemstone. A gemologist can tell you:

• whether the stone is natural or lab-created (Note: lab-created diamonds are still diamonds, just not “natural.” Refer to the section on testing lab-created diamonds for more details).
• if the stone has been color-treated.
• if the stone has undergone long-term or temporary heat treatments.
• how the stone matches the grading documentation provided by the retailer.

Request an appraisal certificate. Regardless of the testing method you choose, the most reliable way to prove a diamond’s authenticity is through documentation and consultation with a gemologist or appraiser. Certification and grading ensure your stone has been “proven” by experts. This is particularly crucial if you’re purchasing a stone sight unseen, such as online. Always ask to see the certificate.

• The best way to appraise a diamond is to request certification from an organization like the Gemological Institute of America (GIA). If they have a branch near you, you can bring the diamond directly or ask a jeweler to send it to GIA.

Examine your documents carefully—not all certificates are equal. Certificates should come from grading organizations (e.g., GIA, AGSL, LGP, PGGL in the U.S.) or an independent appraiser affiliated with a professional body (like the American Society of Appraisers), not from a retail store.

• Certificates include detailed information about your diamond, such as carat weight, measurements, proportions, clarity, color grade, and cut.
• Certificates may contain unexpected details, such as:
  • Fluorescence, or the diamond’s tendency to emit a faint glow under ultraviolet light.
  • Polish, or the smoothness of the surface.
  • Symmetry, or how perfectly the facets align and reflect each other.

Register your diamond. Once you’re certain your diamond is real, whether through independent appraisal or lab grading, take it to an authorized laboratory for registration and gemstone fingerprinting. This ensures the diamond is uniquely yours and cannot be swapped without your consent.

• Like humans, every diamond is unique. Advanced technology allows gemologists to quantify this uniqueness by creating a gemstone “fingerprint.” Registration typically costs less than 2.5 million and includes insurance benefits. If a diamond with your fingerprint is stolen, it will appear in an international database, and you can reclaim it by providing proof of ownership.