How to Tell If a Diamond Is Real: Simple Tests You Can Do At Home

Are you considering purchasing diamond jewelry? Whether it’s a gift for yourself or a special someone, ensuring you’re buying a genuine diamond is crucial. Diamonds represent a significant investment, and the last thing you want is to pay for something that isn’t the real deal.

Fortunately, determining if a diamond is real doesn’t require professional tools or expertise. While jewelers have advanced methods, several simple tests can be performed at home to help you verify a diamond’s authenticity. Here are some practical tips to help you distinguish a real diamond from a fake.

1. The Luster Test

Luster refers to how light interacts with the surface of a gemstone and reflects back to the eye. A diamond’s luster is described as “adamantine,” meaning it’s exceptionally bright and reflective, like a mirror. This high refractive index is a key characteristic of real diamonds.

To perform a luster test:

Clean the diamond: Ensure your diamond is clean and free of oils or dirt, as these can affect light reflection.
Observe light reflection: Hold the diamond under a normal light source, like a lamp, and observe how light reflects off its facets.
Real Diamond Luster: A real diamond will exhibit a brilliant luster, reflecting light intensely. The facets should appear sharp and distinct, radiating brightness.
Fake Diamond Luster: Fakes, like cubic zirconia (CZ) or glass, often have a less intense luster, sometimes described as glassy or dull. Their facets may not be as sharp, and the overall brilliance will be lacking.

While luster alone isn’t definitive proof, a noticeably dull luster is a strong indicator that the stone might not be a real diamond.

2. Check the Color

Diamond color grading is based on the absence of color, ranging from D (colorless) to Z (light yellow or brown). While completely colorless diamonds (D-F range) are the most prized and expensive, slight color variations are common in natural diamonds.

Color Scale: Diamonds are graded on a color scale from D to Z, with D being colorless and Z having a light yellow or brown tint.
Common Grades: Most diamonds used in jewelry fall within the J to M range, exhibiting slight tints of color.
Desirable Color: Many people prefer diamonds that appear white or colorless, typically found in the D to H color range.
Fancy Colored Diamonds: Diamonds also occur in vibrant colors like yellow, pink, blue, and red. These “fancy colored diamonds” are graded on a separate scale and can be incredibly valuable.

When assessing color for authenticity:

Slight Color is Normal: A slight tint of yellow or brown doesn’t necessarily mean a diamond is fake. Many real diamonds have subtle color.
Look for Excessive Colorlessness in Larger Stones at Low Prices: Be wary of large diamonds marketed as perfectly colorless (D-F) at unusually low prices. These could be synthetic or simulants.
Consider the Setting: The setting can influence perceived color. For example, yellow gold settings can make slightly tinted diamonds appear whiter.

3. The Reflection Test (Brilliance Test)

A diamond’s brilliance, or reflection, is a key indicator of its quality and authenticity. Diamonds are cut to maximize light reflection, allowing light to enter, bounce around internally, and exit in a dazzling display.

To assess reflection:

Hold the diamond face-up: Position the diamond under a direct light source.
Observe light return: Look at the amount of light reflected back to your eye.
Real Diamond Reflection: A real diamond exhibits high brilliance, reflecting a significant amount of light. You should see bright white light (brilliance) and colorful flashes of light (fire or dispersion).
Fake Diamond Reflection: Simulants like CZ or glass often lack the same level of brilliance and fire. They may appear sparkly but less vibrant, with less contrast between light and dark areas.

The “Read-Through” Test:

Place the diamond on a newspaper: If you can clearly read the print through the stone, it’s likely a fake.
Real Diamond Refraction: A real diamond bends light so strongly that you shouldn’t be able to clearly see print through it. It will appear blurry or distorted.

4. Weight and Density

Diamonds are dense materials due to their carbon structure. While you can’t determine authenticity by weight alone, density differences can offer clues when comparing stones of similar size.

Diamond Density: Diamonds have a relatively high density compared to many simulants.
Weight Comparison: If you have two stones of similar size and appearance, the real diamond will likely feel heavier.

This test is less precise at home without calibrated tools but can be a subtle indicator when comparing stones side-by-side.

5. The Fog or Breath Test

This simple test relies on diamond’s excellent thermal conductivity. Diamonds disperse heat rapidly, unlike some simulants.

To perform the fog test:

Breathe on the diamond: Exhale on the diamond, fogging it up like you would a mirror.
Observe the fog dissipation: Time how quickly the fog disappears.
Real Diamond Response: The fog on a real diamond should dissipate almost instantly (in 1-2 seconds).
Fake Diamond Response: On a fake like CZ or glass, the fog will linger for several seconds (3-5 seconds or longer) because they retain heat longer.

This test is a quick and easy way to differentiate diamonds from materials with lower thermal conductivity.

6. Hardness and Scratch Test (Use with Caution!)

Diamonds are the hardest naturally occurring substance, scoring a 10 on the Mohs Hardness Scale. This exceptional hardness is a defining characteristic.

Mohs Scale: Diamonds are at the top of the Mohs scale, meaning they can scratch almost any other material.
Scratch Test (Caution Advised): Traditionally, a diamond could scratch glass (Mohs 5.5). However, this test is risky and not recommended for valuable or potentially real diamonds. It can damage both the diamond (if misidentified as a softer stone) and the item being scratched.
Modern Simulants: Some modern diamond simulants, like moissanite, are also very hard and can scratch glass, making this test less reliable.

Safer Hardness Assessment:

Check for Scratches on the Diamond: A real diamond should be very resistant to scratches. If you see surface scratches, it might be a softer simulant. However, even diamonds can chip or get surface blemishes over time, so this isn’t foolproof.

Due to the risk of damage and the availability of better tests, the scratch test is generally discouraged.

7. The Thermal Conductivity Probe (Diamond Tester)

For a more definitive at-home test, a diamond tester (thermal conductivity probe) is a worthwhile investment if you frequently buy or assess diamonds.

How it Works: These handheld devices measure the rate at which heat passes through a stone. Diamonds are exceptional thermal conductors.
Using a Diamond Tester: Simply touch the probe to the stone. A real diamond will register a high thermal conductivity reading, usually indicated by lights or a sound on the tester.
Testing Moissanite: More advanced testers can also differentiate diamonds from moissanite, another popular simulant that can sometimes pass basic diamond tests.

Limitations:

Not Foolproof on Lab-Grown Diamonds: Some older testers may not distinguish between natural and lab-grown diamonds, as both are real diamonds with identical properties. However, newer, more sophisticated testers can often identify lab-grown diamonds.

8. The UV Fluorescence Test

Some diamonds fluoresce under ultraviolet (UV) light, meaning they emit a visible glow.

UV Light Reaction: When exposed to UV light (like a blacklight), some diamonds will emit a blue fluorescence. Others may fluoresce yellow or green, or not at all.
Fluorescence as an Indicator: A strong blue fluorescence can be an indicator of a real diamond, but its absence doesn’t necessarily mean it’s fake.
Not Definitive: Some fake diamonds can be treated to fluoresce, and many real diamonds don’t fluoresce strongly or at all. This test is best used in conjunction with other methods.

How to Perform a UV Test:

Use a UV Light Source: A blacklight or UV flashlight is needed.
Observe in a Dark Room: Examine the diamond under UV light in a darkened room.
Look for Fluorescence: Check for a blue, yellow, or green glow.

9. The Fire Test (Extreme Caution!)

This test is potentially damaging and should be performed with extreme caution and only as a last resort on stones you are highly suspicious of.

Diamond’s Heat Resistance: Diamonds are incredibly resistant to heat.
The Fire Test (Risky): Heat the stone with a lighter flame for about 30-40 seconds and then immediately drop it into cold water.
Real Diamond Result: A real diamond should withstand this extreme temperature change without damage.
Fake Diamond Result: Many simulants, like CZ or glass, will shatter or crack due to thermal shock from rapid heating and cooling.

Risks and Warnings:

Potential Damage: Even though diamonds are durable, extreme thermal stress could potentially cause damage, especially to stones with existing inclusions or weaknesses.
Safety Precautions: Handle heated stones with care and use appropriate safety measures.
Not Recommended for Valuables: Do not perform this test on diamonds you are certain are real or are of significant value.

This test is only for verifying very questionable stones where other methods are inconclusive.

Conclusion: Combine Tests and Seek Professional Verification

While these at-home tests can provide strong indications, no single test is completely foolproof. For valuable diamonds or when you need absolute certainty, professional verification is always recommended.

Jeweler Appraisal: A qualified jeweler has the expertise and tools to accurately assess a diamond’s authenticity and quality.
Gemological Labs: For high-value diamonds, consider sending them to a reputable gemological laboratory (like GIA, AGS, or IGI) for certification. A diamond certificate provides a detailed report of the diamond’s characteristics, including whether it is natural or lab-grown.

Key Takeaway: When purchasing diamonds, especially significant investments, buy from reputable jewelers and ask for certification. For existing diamonds you’re unsure about, use these tests cautiously as preliminary checks, but always prioritize professional evaluation for definitive confirmation.

Are you uncertain about the authenticity of your diamond? Bring it to London Gold for expert inspection and testing. For diamonds over 0.5 carats, we can also assist in sending your diamond to an internationally recognized lab for certification.

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