Lab-Grown Guide · Updated June 2026
Do Lab-Grown Diamonds Pass a Diamond Tester?
Yes — lab-grown diamonds pass a diamond tester. A standard thermal tester reads them as “diamond” because they are diamond: pure crystalline carbon with identical heat conductivity to a mined stone. The catch is the opposite of what most people expect — a tester confirms the stone is a real diamond, but it cannot tell whether that diamond was grown in a lab or mined from the earth.
Why they pass: how a diamond tester actually works
A handheld thermal diamond tester doesn’t detect “realness” — it measures thermal conductivity, how quickly a material draws heat away from a warmed probe tip. Diamond conducts heat better than almost any other material, which is what sets it apart from cubic zirconia and glass. Because a lab-grown diamond is the same material — carbon arranged in the same cubic crystal lattice — it conducts heat identically and trips the “diamond” reading every time.
The U.S. FTC formally recognizes lab-grown diamonds as diamonds, and they share every physical property that matters to a tester: Mohs 10 hardness, the same refractive index, the same density. There is nothing for a conductivity probe to find that would flag them as different.
What a tester can’t do
A pocket tester answers one question — is this diamond? — and stops there. It cannot:
- Separate lab-grown from natural. Both are diamond, so both pass. Origin is invisible to a conductivity probe.
- Grade the stone. It says nothing about color, clarity, cut, or carat.
- Always catch moissanite. Thermal-only models can misread moissanite as diamond; a combination tester with an electrical probe corrects that.
Telling lab-grown from natural requires lab equipment — photoluminescence and spectroscopy that read the trace growth signatures left by CVD/HPHT versus geological formation. That’s why every reputable lab-grown stone ships with an IGI or GIA report and a laser inscription on the girdle.
How to actually confirm origin
If you need to know lab-grown from natural — for insurance, resale, or peace of mind — rely on the paperwork, not a tester:
- Read the report. A lab-grown grading report is explicitly headed “Laboratory-Grown Diamond Report.”
- Check the girdle inscription under magnification — it carries the report number and, for lab-grown, a “laboratory-grown” note.
- Have a gemologist verify it with spectroscopic screening. We do this in our Snellville showroom and can source either type to spec.
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Not Sure What's in Your Ring?
Bring it to our Snellville showroom near Atlanta. We'll test the stone, confirm whether it's diamond, and — with the right equipment — tell you lab-grown from natural.