Do Lab Grown Diamonds Pass a Diamond Tester?

Short answer: yes. A lab grown diamond passes a standard diamond tester, every time, because it is a diamond.

The longer answer is more useful, because it explains what these tools can and cannot tell you.

What a diamond tester measures

Most handheld testers measure thermal conductivity. Diamond conducts heat better than almost any other material, so the probe reads how fast heat moves away from the tip.

A lab grown diamond has the same carbon crystal structure as a mined one, so it conducts heat identically and reads as diamond. There is no test a jeweler can perform with a handheld tool that separates the two. Distinguishing them requires laboratory equipment that looks at growth patterns and trace elements.

Where moissanite comes in

Moissanite is silicon carbide, not carbon, but its thermal conductivity is close enough to diamond that older thermal-only testers read it as diamond too. That is why dual testers exist: they add an electrical conductivity check, and moissanite conducts electricity while diamond does not.

So:

• Thermal tester alone: diamond passes, lab diamond passes, moissanite often passes too

• Thermal plus electrical tester: separates moissanite from both diamonds

• Neither: separates a lab grown diamond from a mined one

What this means when you buy

If someone tells you a stone "passed the diamond tester," that tells you it is probably diamond or moissanite. It does not tell you whether it was grown or mined, and it says nothing about quality.

The document that matters is the grading report. Lab grown diamonds are certified by IGI and other labs on the same cut, color, clarity and carat scale as mined stones, and the report states plainly that the stone is laboratory grown.

Why this question comes up so often

Buyers worry that a lab grown diamond will be "found out" — by a jeweler, an insurer or a relative. It won't, because there is nothing to find out. It is a diamond. The only difference is where it formed and what it cost.

Frequently asked questions

Can a jeweler tell a lab grown diamond by eye?

No. Neither can a gemologist with a loupe. Identification needs specialist instruments, which is why lab grown stones carry a laser inscription on the girdle.

Will insurance treat a lab grown diamond differently?

Insurers cover it at its appraised value, which is lower than a comparable mined stone. Get an appraisal and keep the certificate.

Does moissanite fail a diamond tester?

On a modern dual tester, yes, it is identified as moissanite. On older thermal-only testers it frequently reads as diamond.

Are lab grown diamonds graded like mined diamonds?

Yes, on the same scale, typically by IGI. The report states that the stone is laboratory grown.

Browse lab grown diamond jewelry in solid gold, or compare the two stones in lab grown diamonds vs moissanite.