It is the question every new Moissanite owner secretly asks: If I take this ring to a jeweler, will their machine tell them it’s not a diamond?
The short answer is: Yes, Moissanite will pass almost all standard diamond testers.
If you touch a standard thermal tester to a Moissanite stone, it will light up green and beep, identifying the stone as a Diamond.
But why does this happen? Is the machine broken? Is Moissanite actually a diamond? —No.
At La Pretti, we believe knowledge is power. Today, we are diving into the science of gemology to explain why Moissanite is the ultimate impostor to technology, and the one specific tool that can actually tell them apart.
Why Moissanite Tricks the Tester Science
To understand why Moissanite passes, you have to understand how those little black testing pens work.
✍️Most standard diamond testers like popular Diamond Selector II found on Amazon are Thermal Conductivity Probes.
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How they work: Tip of the pen heats up. When it touches a gemstone, it measures how fast that heat travels through the stone.
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Diamonds: Are excellent conductors of heat. They pull heat away from the tip instantly.
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Glass/CZ: Are insulators. They hold the heat.
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Moissanite: Here is the kicker—Moissanite is extremely similar to Diamond in thermal conductivity.
Because Moissanite is composed of Silicon Carbide, it conducts heat almost exactly like a carbon Diamond. The tester feels the cold, fast transfer of heat and assumes, This must be a diamond!
Takeaway: Moissanite passes the tester not because it is fake, but because it shares the same high-performance physical properties as a diamond.
So, Can Anything Tell Them Apart?
Yes😼While standard heat pen will be fooled, professional jewelers in 2026 often use a more advanced device called a Multi-Tester.
This device measures two things:
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Thermal Conductivity: Heat
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Electrical Conductivity: Electricity
This is where Moissanite gets caught.
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Natural Diamonds generally do not conduct electricity well.
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Moissanite does conduct electricity because it is a semiconductor.
When a jeweler uses a Multi-Tester, that machine sends a tiny electrical current through the stone. If the stone conducts the electricity, that machine knows it is Moissanite, not a Diamond.
🎭Why Cubic Zirconia /CZ Fails Immediately
This is important to note. If you buy a cheap Cubic Zirconia ring, it will fail standard diamond tester every time.
CZ is an insulator just like glass. It does not conduct heat. The moment tester touches a CZ stone, the machine will stay silent or buzz to indicate Simulant.
The fact that Moissanite passes thermal test is proof of its superior quality. It proves that Moissanite is a hard, dense, high-quality gemstone, far superior to glass or plastic simulants.
Can You Test It at Home?—Fog Test
If you don't have a tester pen, there is an old-school trick you can try: Fog Test.
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Clean your stone perfectly.
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Hold it close to your mouth and breathe on it like fogging a mirror.
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Watch how fast the fog disappears.
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Diamond & Moissanite: Because they conduct heat so well, the fog should disappear instantly almost before you can look at it.
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Cubic Zirconia: Fog will sit on the surface for a few seconds because the stone holds the heat.
Note: This isn't scientific, but it’s a fun party trick!
Wear It With Confidence
The fact that Moissanite passes a diamond tester shouldn't be a source of anxiety—actually it should be a source of pride🩷.
It confirms that you are wearing a gemstone that is physically closer to a diamond than any other stone on earth. It is hard, it is heat-resistant, and it is ethically brilliant.
Unless someone walks around with a laboratory-grade electrical conductivity meter in their pocket which they don't, your secret is safe.
Ready to own the gem that fools the experts? Explore La Pretti collection of tester-passing, VVS1 Moissanite.
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