A generation ago, a thermal diamond tester answered the counter’s big question in two seconds. Then moissanite arrived… a stone that passes thermal testing… and the two-second answer became a two-part discipline. If your counter buys, appraises, or takes in trade, your testing equipment needs to reflect the market that actually exists in 2026.
Why thermal alone is no longer enough. Classic testers read thermal conductivity, and diamond’s is famously exceptional… but moissanite’s is close enough to pass. With moissanite now everywhere (sold honestly and otherwise), a thermal-only pass proves a stone is diamond OR moissanite. That is not an answer you can buy on.
The two-step counter standard. Step one: thermal test separates diamond/moissanite from glass, CZ, and most simulants. Step two: a moissanite tester (reading electrical conductivity) separates diamond from moissanite. Multi-testers combine both readings in one probe and have become the sensible default for busy counters… one device, one workflow, a trustworthy answer.
Technique still matters. Clean the stone (skin oils skew readings), test on the table facet, keep the probe perpendicular, let the device warm up, and test mounted stones with the metal-alert function in mind… touching a prong reads as metal, not stone. And know the limits: lab-grown diamond IS diamond to every conductivity tester. Distinguishing natural from lab-grown is a different tier of equipment and a different conversation with your customer.
Buying right. A quality multi-tester is not a place to save forty dollars… it is the device standing between your counter and an expensive mistake. We stock trade-grade diamond and moissanite testers, and we will happily talk you through which model fits your volume.
Equip the counter properly… browse our gem testing tools or call (210) 341-7783 for a recommendation.