Can a Diamond Tester Detect a Lab-Grown Diamond?

Short answer: The diamond testers jewellers use can tell whether a stone is a diamond, but not whether it is natural or grown in a laboratory. A lab-grown diamond is a real diamond and conducts heat the same way, so the tester shows it as “diamond” too. Telling natural from lab-grown diamond takes advanced instruments in gemmological laboratories, which is why the stone’s report is decisive.

How does a diamond tester work?

Thermal conductivity

Diamond conducts heat extremely well. A heat-measuring tester (thermal tester) measures how fast heat spreads when its tip touches the stone. Cubic zirconia, glass and most imitation stones do not conduct heat well, so the tester picks them out at once. Cubic zirconia versus diamond.

The moissanite problem and electrical conductivity

Moissanite also conducts heat well, so a tester that only measures heat may mistake it for diamond. That is why “multi-testers” also measure electrical conductivity: moissanite conducts electricity, while most diamonds do not. What is moissanite?

What does a lab-grown diamond show on a tester?

A lab-grown diamond shows as diamond on heat testers, because it is a real diamond. On multi-testers it usually shows as diamond too. There is a rare exception: some diamonds with trace amounts of boron in their crystal (some natural blue diamonds and some lab-grown diamonds) can conduct electricity slightly, and simple testers may wrongly show them as moissanite. This does not mean the stone is not a diamond; it is a limit of the tester.

How do you tell natural from lab-grown diamond?

This distinction is made by looking at very fine differences in the stone’s crystal: growth patterns, trace elements and patterns under ultraviolet light. The tools used for this are:

• Spectroscopy: Measures how the stone absorbs light and determines the diamond’s “type”.
• Ultraviolet imaging: Shows growth patterns under short-wave UV light; natural and lab-grown stones have different patterns.
• Screening devices: Quickly scan large numbers of small stones and set aside those that need further examination.

These instruments are found mostly in gemmological laboratories. The result is written on the stone’s report as “laboratory-grown” or “natural”. How to read a certificate.

Can you test at home?

Home tests such as fog, water and read-through tests are not conclusive, and telling a lab-grown diamond from a natural one at home is impossible. The surest way to know a stone is real is its report, and the report number matching the laser inscription on the stone’s girdle. How to tell if a diamond is real.

When having a stone tested at a jeweller

• Ask which tester is used: heat only, or heat and electricity?
• Remember that the tester saying “diamond” does not mean the stone is natural.
• If you want to know the origin, have the stone examined by an independent gemmological laboratory.

Frequently asked questions