If you own a lab-grown diamond, or you're thinking of buying one, you may wonder what happens when a jeweler checks it with a diamond tester. The short version is reassuring, with one technical exception worth knowing about. Here's how diamond testers work, what they can and can't tell you, and how lab-grown diamonds are actually identified.
Do lab-grown diamonds pass a diamond tester?
Yes. Lab-grown diamonds pass standard diamond testers because they're the same material as mined diamonds and conduct heat the same way. A thermal tester can't tell lab-grown from natural. One exception: some HPHT-grown diamonds containing traces of boron can read as moissanite on testers that also check electrical conductivity. Gem labs use specialized equipment to identify lab-grown stones.
How does a diamond tester work?
Most handheld diamond testers measure one or both of these properties:
- Thermal conductivity. Diamond moves heat away from a heated probe tip much faster than almost any other gemstone. Glass, cubic zirconia, white sapphire and most simulants fail this test.
- Electrical conductivity. Moissanite also conducts heat well, so it can fool a thermal-only tester. Multi-testers add an electrical check because moissanite conducts electricity and most diamonds don't.
Diamond tester results by stone
| Stone | Thermal tester | Multi-tester (thermal + electrical) |
|---|---|---|
| Natural (mined) diamond | Diamond | Diamond |
| Lab-grown diamond (CVD) | Diamond | Diamond |
| Lab-grown diamond (HPHT) | Diamond | Usually diamond; some boron-containing stones read as moissanite |
| Moissanite | Often reads as diamond | Moissanite |
| Cubic zirconia | Not diamond | Not diamond |
| White sapphire, glass, crystal | Not diamond | Not diamond |
Why do some lab-grown diamonds test as moissanite?
Some lab-grown diamonds grown by the HPHT (high pressure, high temperature) method absorb small amounts of boron as they form. Boron makes a diamond slightly electrically conductive. That's exactly the property a multi-tester uses to flag moissanite, so the tester can call a diamond "moissanite". The stone is still a diamond; the tester simply can't account for it. If you get this result, an independent grading report or a gem lab will confirm what the stone is. Learn more about growth methods in our CVD vs HPHT guide.
Can a jeweler tell if a diamond is lab-grown?
Not with a standard tester, a loupe or the naked eye. Lab-grown and mined diamonds look the same and test the same on handheld thermal testers. Telling them apart requires specialized screening instruments, which detect tiny differences in growth patterns, trace elements and how the stone reacts to ultraviolet light. Gem labs such as IGI and GIA, and many larger jewelers, use these instruments. The simplest check is often the stone's paperwork. Lab-grown diamonds graded by IGI or GIA usually carry a report that identifies them as laboratory-grown, and many have the report number laser-inscribed on the girdle (the thin outer edge), visible under magnification.
How can you verify a lab-grown diamond?
- Check the grading report. It should state that the diamond is laboratory-grown and list its 4Cs grades.
- Look up the report number on the issuing lab's website (IGI or GIA) to confirm the report is genuine and matches your stone.
- Match the laser inscription. Ask a jeweler to view the girdle under magnification and compare the inscribed number with the report.
- For certainty, use a gem lab. If a tester result is unexpected, a gemological lab can identify the stone definitively.
Frequently asked questions
Will a lab-grown diamond pass a jeweler's diamond tester?
Yes. A lab-grown diamond tests as diamond on a standard thermal tester, because it's the same material as a mined diamond. A small number of HPHT stones may read as moissanite on multi-testers because of trace boron.
Does moissanite pass a diamond tester?
It often passes a basic thermal tester, because moissanite conducts heat similarly to diamond. A multi-tester with an electrical check identifies it as moissanite. See moissanite vs lab-grown diamond.
Do cubic zirconia stones pass a diamond tester?
No. Cubic zirconia fails a diamond tester. Read more in lab-grown diamond vs cubic zirconia.
Can a diamond tester tell lab-grown from natural?
No. Standard handheld testers can't distinguish them. That takes specialized screening equipment or a gem lab, which is why independent certification matters.
Are MIRA Studio's lab-grown diamonds certified?
Yes. Every lab-grown diamond we sell is IGI or GIA certified, with the grading details listed on the product page. Learn the difference between the two labs in IGI vs GIA certification.
Explore certified lab-grown diamonds
Browse certified loose lab-grown diamonds or Lab Diamond Rings, or learn how diamonds are graded in the 4Cs explained.
