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How to Test a Diamond at Home

Understanding the materials and characteristics unique to real diamonds and synthetic diamonds can help you to determine if the diamond in question is real or synthetic. 

Diamond: Naturally occurring mineral composed of pure carbon found geologically in kimberlite pipes, alluvial gravel, and glacial tills.

Cubic Zirconia: Cubic zirconia (CZ) is Zirconium Dioxide (ZrO₂) in its cubic crystalline form.  It a gemstone simulant, which means it is laboratory grown and has a similar appearance to the diamond but possesses different visual, physical, and chemical properties. ["Gemstones - Synthetic and Simulant" usgs.gov]

Moissanite: Also known as silicon carbide, moissanite was originally a naturally occurring mineral that looked very similar to the diamond.  Because of its scarcity, today all silicon carbide is made from synthetic materials. ["What Is Moissanite?" moissanite.com]

Refractive Index

The ability of a substance to bend or refract light is measured by the refractive index.  The diamond's unique anatomical structure in conjunction with the other natural minerals occurring within the rock bend light as it passes through even though it appears to be transparent.  This gives the diamond its unique fire and brilliance. Cubic zirconias are cut to mimic this light refraction but usually cannot come close.

How to Use This Property at Home: According to Fred Cuetter best-selling author of How to Buy Diamonds you can tell if your diamond is real by turning it upside down and placing it on top of printed material, such as a magazine or newspaper.  You should not be able to see the print through a diamond.

Thermal Conductivity

 An object's ability to transfer heat is known as thermal conductivity.  The cubic zirconia, like most transparent objects, does not conduct heat well, whereas the diamond is an extremely efficient thermal conductor.  Jeweler's instruments use this fact to distinguish between a real and a fake diamond. ["World of Carbon", invsee.asu.edu]

How to Use This Property at Home: You can test this property at home with the fog test.  Breathe onto your stone and observe how quickly the fog dissipates.  The diamond should conduct the heat immediately leaving no fog behind.  An imitation will not be able to conduct the heat as efficiently leaving the stone foggy for a few seconds.

Scratch Hardness

In theory, you can use the Moh's scale of mineral hardness to determine if your diamond is real or fake.  The Moh's scale is a classification system to determine a mineral's hardness based on the ability of harder materials to scratch softer materials.

Diamond: A diamond is the hardest naturally occurring material at 10 on the Moh's scale.  Harder than both the cubic zirconia and moissonite means that either can be scratched by a real diamond.

Cubic Zirconia: A cubic zirconia has a hardness of 8.5, which means that though it is hard it can still be cut by gems that are higher on the Moh's scale such as the diamond, ruby, or sapphire . [Weathers, cornell.edu]

Moissanite: With a 9.25 on the Moh's scale, moissanite is at the upper end of the Moh's hardness scale.  Though particularly hard, it can still be scratched by a real diamond. [Weathers, cornell.edu]

How to Use This Property at Home: The problem with this method of detection is that you run the risk of ruining a perfectly good stone if it's not real diamond.  You also run the risk of damaging the diamond because though it may not scratch, it's setting may.  In addition, a diamond can be scratched by another diamond. [Aber, emporia.edu]

Professionals Are Best

Though the methods you use at home may give you some indication if your diamond is real, nothing can replace taking it a professional who has the correct equipment and knowledge to determine a gem's authenticity.