Can a Lab-Grown Diamond Pass a Diamond Tester?

ZKZ Editorial TeamMain answer · Product & gemmology desk

Usually yes. A lab-grown diamond is diamond, so it passes a thermal tester the same way a mined diamond does. But a pass only says “diamond-like material”; it says nothing about origin. And a minority of lab-grown stones, mainly HPHT-grown ones containing trace boron, can read “moissanite” on electrical or multi-testers. That reading is a reason to escalate, not proof of a fake.

Why the two readings can differ

Fact Thermal testers measure how fast heat leaves a probe tip. Natural and lab-grown diamond share the same thermal conductivity, so both read as diamond. IGI notes that thermal testers make no distinction between the two.

Fact Electrical testers were added because moissanite also conducts heat well. Diamond normally does not conduct electricity, but boron does make it conductive. GIA reported that more than 80% of colourless HPHT-grown diamonds it examined since 2020 contained detectable boron. Metallic flux remnants from HPHT growth can also affect readings (IGI). A conductive diamond can therefore trigger the “moissanite” alert.

What to do with a mixed result

1. Clean and dry both stones and repeat the test at the correct probe angle. Oil, dirt and very small stones cause unreliable readings.
2. Check the paperwork: an independent report number and any girdle inscription can be looked up on the lab’s website.
3. Have a gemmologist look under magnification. Moissanite is doubly refractive, so facet edges look doubled at certain angles. Diamond is singly refractive.
4. If doubt remains, ask a laboratory for identification. Only lab-grade instruments separate natural from lab-grown diamond reliably.

Where the limits are

Our advice Treat any handheld result as a screen. It can rule out glass and cubic zirconia, it usually flags moissanite, and it cannot judge origin at all. Do not use a tester result to decide whether a seller disclosed origin correctly. Under the FTC Jewelry Guides, a laboratory-grown diamond should be described with a qualifier such as “laboratory-grown” placed immediately before “diamond”, so the disclosure should already be on the listing and invoice.

Uncertain Tester models differ in sensitivity. We cannot say how any specific device will respond to a specific stone, so a repeat “moissanite” result needs a lab check rather than an assumption either way.

Sources

• IGI: Diamond detection and handheld testers
• GIA, Gems & Gemology (Summer 2024): Laboratory-Grown Diamonds, an update on identification
• FTC: In the Loupe, advertising diamonds, gemstones and pearls
• 16 CFR 23.12, FTC Jewelry Guides: definition of "diamond"

Fact = stated by the cited source. Our advice = editorial recommendation. Uncertain / it depends = limits of what can be said in general.