Yes. Lab-grown diamonds pass a diamond tester. A standard tester measures how well a stone conducts heat, and because a lab-grown diamond is made of the same carbon as a mined diamond, it conducts heat the same way and reads as diamond. A tester confirms a stone is a diamond. It does not, and cannot, tell you whether that diamond was grown in a lab or mined. If you own a pen-style tester, or you are worried a jeweler’s test might expose a lab-grown stone as not a real diamond, this guide explains what the test checks, why lab-grown diamonds pass, and where the common testers actually get confused.
How a diamond tester works
A common diamond tester is a thermal probe. Diamond conducts heat better than almost any other material used in jewelry, so the tester sends a small amount of heat into the stone and measures how fast it moves through. If the heat disperses the way it does in diamond, the tester signals “diamond.” That is the entire test: thermal conductivity, not origin.A lab-grown diamond has the identical carbon crystal structure as a mined diamond, so its thermal conductivity is identical. The tester has no way to separate the two, because there is nothing thermally different to detect.A diamond tester answers one question: is this a diamond? For a lab-grown stone, the answer is yes.
Why lab-grown diamonds pass every standard tester
A lab-grown diamond passes because it is a real diamond, chemically and physically. Thermal testers, and the newer combined thermal-and-electrical testers, are built to sort diamonds from lookalikes such as cubic zirconia and glass. Lab-grown stones are not lookalikes. They are the genuine material, so they clear the test the same way a mined diamond does.This is worth stating plainly, because the fear behind the question is that a lab-grown diamond will fail and be revealed as fake. It will not. Passing a diamond tester is evidence the stone is a real diamond, which a lab-grown diamond is. A passing result is reassurance, not a risk.
Where testers do get confused: moissanite
The one lookalike that fools older testers is moissanite. Moissanite is silicon carbide, and it conducts heat well enough that a basic thermal-only tester can misread it as diamond. This is a moissanite problem, not a lab-grown-diamond problem. To handle it, many modern testers add an electrical conductivity probe, because moissanite conducts electricity and diamond does not.
Here is how the common results shake out on a combined tester:
| Stone | Thermal test | Electrical test | Reads as |
|---|---|---|---|
| Lab-grown diamond | Passes as diamond | Non-conductive | Diamond |
| Mined diamond | Passes as diamond | Non-conductive | Diamond |
| Moissanite | Can pass on thermal alone | Conducts | Moissanite (modern testers) |
| Cubic zirconia | Fails | Fails | Not diamond |
The practical point: a combined tester tells lab-grown and mined diamonds apart from moissanite and cubic zirconia. It still does not separate lab-grown from mined, because on both the thermal and electrical checks they behave identically.
What actually identifies a lab-grown diamond
If a tester cannot reveal origin, what can? Two things:
- The certificate. A report from the GIA or the IGI states whether the stone is laboratory-grown, and reputable lab-grown diamonds carry a laser inscription of the report number on the girdle, readable under magnification.
- Specialized lab instruments. Grading labs read growth features and fluorescence to confirm origin, which is how they classify a stone as lab-grown in the first place.
So the honest answer to “can anyone tell it is lab-grown” is: not with a pocket tester, and not by eye, but yes with the certificate or with lab equipment. The catch? A pen tester was never designed to answer the origin question. It answers “is this a diamond,” and for a lab-grown stone the answer is yes.
The bottom line
A diamond tester confirms your lab-grown stone is a real diamond, because it is one. It cannot expose it as fake, and it cannot reveal that it was grown rather than mined. Only the certificate and the laser-inscribed report number do that, and a good seller gives you both up front.At Candor Diamonds, every stone is lab-grown, clearly disclosed, and IGI or GIA certified with the report available to you. There is nothing to catch out, because you already know exactly what you own, down to the report number laser-inscribed on the diamond. Add a lifetime warranty, free insured shipping, and 30-day returns, and you can buy with full confidence.
Frequently asked questions
Do lab-grown diamonds test as real diamonds?
Yes. A standard diamond tester reads a lab-grown diamond as diamond because it is one. The tester measures thermal conductivity, which is identical for lab-grown and mined diamonds.
Can a diamond tester tell lab-grown from mined?
No. A diamond tester confirms a stone is a diamond but cannot tell where it was grown. Separating lab-grown from mined takes a grading lab, or reading the certificate and laser inscription.
Why does moissanite sometimes pass a diamond tester?
Older thermal-only testers can misread moissanite as diamond because it conducts heat reasonably well. Modern testers add an electrical check, which flags moissanite, since moissanite conducts electricity and diamond does not.
Will a jeweler’s tester expose my lab-grown diamond?
No. It will confirm your stone is a real diamond, which it is. If you want origin confirmed, the certificate and the laser-inscribed report number do that.
Is a stone that fails a diamond tester fake?
A stone that fails a thermal tester is not diamond, so it is likely a simulant such as cubic zirconia or glass. A lab-grown diamond does not fail, because it is a genuine diamond.
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