How to test for a real diamond

The Water Test

One of the simplest methods to test a diamond’s authenticity is the water test, which takes advantage of a diamond’s high density. Real natural diamonds are extraordinarily dense compared to most diamond simulants. This test requires nothing more than a glass of water and your stone.

To perform this test, fill a glass with water at room temperature. Carefully drop the loose stone into the glass. A genuine diamond will sink to the bottom due to its density, while many fakes will float or sink more slowly. This test works particularly well for distinguishing diamonds from cubic zirconia, which has a lower density.

However, be aware that some diamond simulants like moissanite also have high densities and may sink similarly to a real diamond. Additionally, if your stone is set in a ring or other jewelry piece, this test won’t be as effective because the metal setting can affect how the piece behaves in water.

While the water test is a good preliminary check, it shouldn’t be your only method of verification. It’s relatively reliable when comparing diamonds to cubic zirconia but may not help distinguish between diamonds and other high-density stones. For a more definitive answer, especially when considering an investment in wedding bands or other significant jewelry, combining several tests or seeking professional evaluation is recommended.

Remember that this test is most effective with loose stones. If your diamond is already set in a piece of jewelry, consider some of the other testing methods we’ll discuss below that don’t require removing the stone from its setting.

The Fog Test

The fog test is another simple at-home method that requires no special equipment and can be performed on mounted stones. This test takes advantage of a diamond’s thermal conductivity properties—diamonds disperse heat rapidly, much faster than most simulants.

To conduct the fog test, hold the stone between your fingers and breathe on it to fog it up, similar to how you would fog a mirror. A real diamond will clear up almost immediately because it conducts heat away from the surface, causing the fog to dissipate quickly. Most diamond simulants, like cubic zirconia or glass, retain heat longer, so the fog will remain on the surface for several seconds.

This test is particularly useful for stones set in bracelets or other jewelry where the water test isn’t practical. However, be aware that moissanite, a popular diamond alternative, also has excellent thermal conductivity and may perform similarly to a diamond in this test.

For best results, make sure your stone is at room temperature before testing. If you’ve been handling it extensively, give it a few minutes to cool down. Also ensure the stone is clean—oils from your skin can affect how moisture condenses on the surface.

While the fog test is convenient and non-invasive, it’s not 100% conclusive. Environmental factors like room temperature and humidity can influence the results. As with the water test, consider this one tool in your verification toolkit rather than a definitive answer on your stone’s authenticity.

The Newspaper Test

The newspaper test evaluates a diamond’s refractive properties—how light bends as it passes through the stone. Due to their unique crystal structure, real diamonds refract light in a way that makes text appear blurry when viewed through the stone.

To perform this test, place a loose stone flat on a piece of newspaper or any printed text. If you can read the letters through the stone, even if they appear somewhat distorted, the stone is likely not a genuine diamond. With a real diamond, the high refractive index causes light to bend so much that text viewed through the stone will appear as an illegible blur.

This test works best with loose, colorless stones. If your stone is mounted in a setting like those found in elegant estate earrings, you may not be able to place it directly on the newspaper. In that case, try holding the jewelry piece close to the text and looking through the stone at an angle.

The newspaper test is particularly effective at identifying glass imitations, which have a much lower refractive index than diamonds. However, some high-quality simulants like moissanite also have high refractive properties, though they refract light differently than diamonds.

For the most accurate results, conduct this test in good lighting conditions. Natural daylight works best, as artificial lighting can sometimes affect how clearly you can see through the stone. Like other at-home tests, the newspaper test should be considered one piece of evidence rather than conclusive proof of a diamond’s authenticity.

The UV Light Test

The UV light test examines how a diamond fluoresces (glows) under ultraviolet light. While not all diamonds fluoresce, approximately 30% of natural diamonds exhibit some degree of fluorescence when exposed to UV light—most commonly a blue glow, though other colors can occur.

To conduct this test, you’ll need a UV light (blacklight). In a dark room, shine the UV light on your stone and observe any fluorescence. While fluorescence can indicate a natural diamond, the absence of fluorescence doesn’t necessarily mean your stone is fake, as many genuine diamonds don’t fluoresce at all.

This test becomes more useful when you know what to expect from specific diamond simulants. For example, cubic zirconia typically shows no fluorescence or a yellow glow, while many synthetic diamonds may fluoresce differently than natural ones. If you’re comparing a stone to known lab diamond jewelry, this test may help identify differences.

The UV light test is non-destructive and can be performed on mounted stones, making it suitable for testing precious pieces like engagement rings without risking damage. However, it’s one of the less conclusive tests because of the variability in diamond fluorescence.

Professional jewelers use more sophisticated fluorescence testing as part of a comprehensive evaluation. If you’re serious about authenticating a valuable diamond, the experts at Espling Jewelers can provide more definitive fluorescence testing as part of a professional appraisal.

The Heat Test

The heat test leverages the exceptional thermal conductivity and durability of diamonds. Real diamonds are one of the most thermally conductive materials on earth and can withstand extremely high temperatures without damage.

Warning: This test involves heat and should be approached with extreme caution. It should only be performed on unmounted stones, as heat can damage jewelry settings and adhesives. It’s generally not recommended for valuable pieces.

If you choose to proceed, use a lighter or flame to heat the stone for about 30-40 seconds, then immediately drop it into a glass of cold water. A genuine diamond will disperse the heat rapidly and remain intact, while many simulants may shatter due to thermal shock or show signs of damage.

This test is particularly effective at identifying glass and some plastic imitations, which will typically show obvious damage. However, high-quality diamond simulants like moissanite can also withstand significant heat, so this test isn’t foolproof.

Given the risks involved, the heat test should be considered a last resort for inexpensive stones of questionable origin. For valuable pieces or stones already set in fine wedding bands or other jewelry, safer testing methods or professional evaluation are strongly recommended. Remember that this test could potentially destroy a fake stone—which might be acceptable for testing a suspicious loose stone but devastating if applied to a treasured family heirloom that turns out to be made of another material.

The Sparkle Test

The sparkle test evaluates how a diamond interacts with light—one of its most distinctive characteristics. Diamonds have unique optical properties that create their famous brilliance, fire, and scintillation (the sparkle and flashes of color when the diamond or light source moves).

To conduct this test, hold the stone under normal lighting and observe how light plays through it. A genuine diamond will exhibit white light (brilliance) reflecting from the surface and colorful flashes (fire) from within. Rotate the stone and notice how the sparkles appear and disappear rather than maintaining consistent reflectivity.

Real diamonds from Espling’s natural diamond collection tend to sparkle gray and white with occasional flashes of color, while diamond simulants often show more rainbow-like effects or a more mirror-like reflection. Cubic zirconia, for instance, typically displays more colorful fire than a diamond of similar size.

The sparkle test is subjective and requires some familiarity with how genuine diamonds look. It helps to compare your stone side-by-side with a known diamond if possible. For those unfamiliar with diamond characteristics, visiting a jeweler to see examples of both real diamonds and common simulants can provide a valuable reference point.

This test works for both loose and mounted stones and causes no damage, making it suitable for testing precious pieces like engagement rings. While not technically precise, experienced observers can often spot fake diamonds by their distinctive light performance characteristics.

Professional Diamond Testing

While at-home tests can provide initial insights, professional testing offers definitive answers about a diamond’s authenticity. Jewelers like Espling Jewelers use specialized tools and expertise to identify genuine diamonds with certainty.

Professional diamond testers measure thermal and electrical conductivity properties unique to diamonds. These handheld devices can quickly distinguish between diamonds and most simulants. More advanced testing might include microscopic examination to identify natural growth patterns versus the perfect patterns of synthetic stones.

For valuable pieces, consider obtaining a professional certificate from a gemological laboratory. Organizations like the Gemological Institute of America (GIA) provide comprehensive diamond grading reports that verify authenticity and assess the 4Cs: carat, cut, color, and clarity. These certificates are particularly important when purchasing significant pieces like engagement rings or lab diamond jewelry.

Professional jewelers can also help identify the specific type of diamond simulant if your stone isn’t genuine. This information can be valuable, as some simulants like moissanite have considerable value in their own right.

The cost of professional testing varies depending on the level of detail required. Basic authenticity testing is often available for free or at minimal cost, especially if you’re considering a purchase from the jeweler. Full gemological certificates for insurance or resale purposes typically involve a fee based on the stone’s size and the level of detail in the report.

Common Diamond Imposters

Understanding common diamond alternatives helps you make informed decisions and better interpret test results. Here are the most prevalent diamond simulants you might encounter:

Cubic Zirconia: The most common diamond simulant, CZ is made from zirconium dioxide. It’s heavier than diamond, has more colorful fire, and is much less expensive. While initially bright, it scratches more easily than diamond and tends to become cloudy over time.

Moissanite: Originally discovered in a meteor crater, today’s moissanite is lab-created silicon carbide. It’s nearly as hard as diamond and has excellent brilliance, but displays more colorful fire. Moissanite is thermally conductive like diamond, so it can pass the fog test and heat test. When examining bracelets or other jewelry with clear stones, looking for moissanite’s distinctive “double refraction” can help identify it.

White Sapphire: A natural alternative to diamonds, white sapphires are durable but lack the same brilliance and fire. They tend to look more transparent and have less sparkle than diamonds.

Glass: Inexpensive and common in costume jewelry, glass is much softer than diamond and scratches easily. It has minimal fire and brilliance compared to diamond.

White Topaz: A natural gemstone that’s clearer than diamond but with much less brilliance. It’s considerably softer and will show wear over time that diamonds would not.

It’s important to note that many of these alternatives have legitimate value as gemstones in their own right. Moissanite, for instance, has grown in popularity for wedding bands and other fine jewelry due to its ethical sourcing and lower cost compared to natural diamonds.

Diamond Care and Maintenance

Once you’ve confirmed that your diamond is genuine, proper care will help maintain its brilliance and value for generations. Diamonds may be the hardest natural substance, but they still require appropriate maintenance.

Regular cleaning is essential to keep your diamond sparkling. A simple solution of mild dish soap and warm water works well for routine cleaning. Use a soft toothbrush to gently scrub the stone, paying special attention to the underside where oils and dirt accumulate. Rinse thoroughly and pat dry with a lint-free cloth. For more