How to Tell if a Diamond Is Real

Determining whether a diamond is real is essential for anyone buying, selling, or inheriting a piece of jewelry. With the rise of high-quality diamond simulants and lab-grown alternatives, distinguishing natural diamonds from imitations requires a combination of simple tests and professional evaluation.

Many assume that spotting a fake diamond is easy, but some simulants—like moissanite—can closely resemble real diamonds to the untrained eye. Whether you’ve received a diamond as a gift, inherited one from a family member, or purchased a second hand piece, knowing how to verify its authenticity can prevent costly mistakes.

The good news is that there are several at-home tests that can help determine if a diamond is real. While none of these methods are foolproof on their own, they provide useful clues before seeking professional verification.

Basic At-Home Tests for Diamond Authenticity

While professional tools provide the most accurate results, these at-home tests can help assess whether a diamond is real using everyday materials.

The Fog Test

Diamonds disperse heat quickly. To perform this test, hold the diamond close to your mouth and breathe on it as you would a mirror. A real diamond will clear up almost instantly, while a fake diamond, such as cubic zirconia, will hold the condensation for a few seconds.

The Water Test

This method relies on a diamond’s density. Fill a glass with water and gently drop the stone in. A real diamond will sink due to its high density, whereas many imitations—such as glass or quartz—will float or sink more slowly.

The UV Light Test

Many natural diamonds exhibit fluorescence under ultraviolet (UV) light. Place the diamond under a UV light or black light and look for a blue glow. While not all real diamonds fluoresce, a strong blue glow can be an indicator of authenticity. However, a lack of fluorescence doesn’t mean the diamond is fake.

The Dot Test

This test checks for a diamond’s ability to refract light. Place a white piece of paper on a flat surface and draw a small dot with a pen. Lay the diamond flat over the dot and look through the stone. If you can see the dot clearly, the diamond is likely fake. A real diamond bends light so intensely that you shouldn’t be able to see the dot at all.

The Sandpaper Test

Diamonds are the hardest naturally occurring material, ranking 10 on the Mohs hardness scale. To check durability, gently rub the stone against a piece of sandpaper. A real diamond will remain unscratched, while softer imitations like cubic zirconia or glass will show signs of wear.

While these tests provide quick ways to assess a diamond’s authenticity, they are not definitive. Some high-quality diamond simulants, such as moissanite, may pass certain tests. For more accurate verification, advanced testing or professional evaluation is recommended.

More Advanced Diamond Tests

If basic at-home tests leave any uncertainty, more advanced methods can help distinguish a real diamond from an imitation. These techniques require closer examination and, in some cases, specialized tools.

Thermal Conductivity Test

Diamonds are excellent conductors of heat, which means they disperse heat almost instantly. This property is the basis for diamond testers, handheld devices that measure thermal conductivity. When placed against the stone, a real diamond will allow heat to dissipate quickly, triggering a positive reading on the tester. Most diamond simulants, except moissanite, fail this test.

Electrical Conductivity Test

While diamonds conduct heat well, only certain types conduct electricity. Moissanite is one of the few materials that can conduct both heat and electricity, making it one of the hardest simulants to differentiate from real diamonds. Professional testers designed to measure electrical conductivity can distinguish between moissanite and a natural diamond.

Magnification Test

Under 10x magnification, a real diamond typically shows natural inclusions—tiny imperfections formed during its growth. These can appear as small crystals, pinpoints, or feather-like structures. Simulants such as cubic zirconia are often flawless or contain air bubbles, which never occur in natural diamonds.

A jeweler’s loupe or a microscope can also reveal facet edges. Real diamonds have sharp, clean-cut edges, while fakes often display rounded or worn facets due to their softer nature.

Newspaper or Read-Through Test

Place the diamond flat side down on a printed newspaper or book page. If the text underneath is readable, the stone is not a real diamond. A diamond’s high refractive index bends light so intensely that it prevents clear visibility of objects through it. This test is particularly useful for verifying larger diamonds with a table large enough to cover text.

These advanced tests provide more reliable results, but some high-quality simulants, particularly moissanite, may still pass certain assessments. For definitive verification, professional evaluation is recommended.

Professional Diamond Verification Methods

If at-home tests are inconclusive, a professional jeweler or gemologist can perform expert verification using specialized tools.

Using a Diamond Tester

Jewelers use diamond testers to measure heat conductivity, which quickly separates diamonds from cubic zirconia and glass. More advanced testers also measure electrical conductivity to distinguish between diamonds and moissanite.

Checking with a Jeweler or Gemologist

A trained gemologist can assess a diamond’s authenticity using specialized equipment, such as:

• Gemological Microscopes – Revealing inclusions, facet sharpness, and polishing marks.
• Spectroscopy Tools – Analyzing how a diamond interacts with light to detect synthetic or treated stones.
• X-ray Fluorescence (XRF) – Distinguishing between real and imitation diamonds based on atomic structure.

Certifications and Laser Inscriptions

Authentic diamonds from reputable grading labs such as the GIA, IGI or GCAL come with certificates detailing their cut, color, clarity, and carat weight. These reports also confirm whether a diamond is natural or lab-grown.

Many certified diamonds have a laser inscription on the girdle—an engraved microscopic number corresponding to their certification report. Jewelers can use a loupe or microscope to check for this inscription as an added verification step.

Professional testing offers the most accurate results, ensuring that diamonds are correctly identified and valued.

Common Diamond Imitations and How to Spot Them

While diamonds have unique optical and physical properties, several materials closely resemble them. Understanding the most common diamond imitations and how to differentiate them can help prevent mistaken purchases.

Cubic Zirconia (CZ)

Cubic zirconia is one of the most common diamond simulants. It is mass-produced, inexpensive, and widely used in costume jewelry.

How to spot it:

• Lower hardness – Scratches more easily than a real diamond.
• Higher dispersion – Produces excessive rainbow-like flashes compared to a diamond’s balanced brilliance.
• Perfect clarity – Unlike real diamonds, CZ stones typically lack inclusions.
• Warm to the touch – Diamonds feel cold due to their high thermal conductivity, while CZ warms up quickly.

Moissanite

Moissanite is the most convincing diamond alternative due to its high hardness and brilliance. It has a higher refractive index than diamonds, which can make it appear even sparklier.

How to spot it:

• Double refraction – When viewed under magnification, moissanite shows a double-image effect along its facet edges.
• Different brilliance pattern – Displays more colorful flashes, while diamonds produce a sharper, balanced sparkle.
• Electrical conductivity – Conducts electricity, whereas most diamonds do not (except Type IIb).

Glass and Quartz

Glass and quartz are softer, lower-cost materials sometimes used in fake diamond jewelry.

How to spot them:

• Scratches easily – A real diamond can scratch glass, but glass cannot scratch a diamond.
• Lacks brilliance – Lacks the high refractive index and sparkle of a diamond.
• Visible bubbles – Glass stones often contain tiny air bubbles, which do not occur in real diamonds.

Lab-Grown Diamonds

Lab-grown diamonds are real diamonds with the same chemical composition as natural diamonds. However, they are created in a controlled environment rather than forming naturally over millions of years.

How to spot them:

• Growth patterns – Often show distinct growth structures under magnification.
• UV fluorescence – Some lab diamonds exhibit unusual fluorescence patterns compared to natural stones.
• Certification – Most reputable lab diamonds are graded separately from natural diamonds and come with specific certification from GIA, IGI, or GCAL.

While many diamond simulants are easy to identify, moissanite and lab-grown diamonds require advanced testing or professional verification to differentiate from natural diamonds.

Final Thoughts on Diamond Testing

Verifying whether a diamond is real requires a combination of tests. Basic at-home methods like the fog test, water test, and dot test provide quick clues, while advanced techniques such as thermal and electrical conductivity testing offer more accuracy.

For definitive verification, a professional jeweler or gemologist can assess the stone using magnification, spectroscopy, and certified grading reports. Checking for a GIA, IGI, GCAL certification and laser inscription also ensures authenticity.

With the increasing quality of lab-grown diamonds and simulants, distinguishing between real and imitation diamonds is becoming more complex. Understanding the unique properties of each type of stone helps buyers make informed decisions and avoid costly mistakes.