Gem Tester II

The Presidium Gem Tester II is a contact instrument, not a metal detector: you touch a retractable thermoelectric probe to the stone and the needle settles on a calibrated analogue scale that reads relative heat conduction. Because every gem species conducts heat at its own rate, a single reading is enough to separate up to 16 common coloured stones and to place diamonds and moissanites at the high end of the dial. Presidium's probe tip measures 0.6 mm — the thinnest in the industry by the maker's own claim — so it reaches stones as small as 0.02 ct, including melee already set in a mounting, and the spring-loaded mount holds probe pressure constant so readings repeat instead of drifting. It is built for jewellers, gold-souk buyers, pawnbrokers and stone dealers who need a fast opinion across the counter. It handles polished, rough and surface-treated material, and needs no waiting time between tests. Glass and Calibration (CAL) reference discs are built into the housing so you can re-check a reading on the spot, and a metal alert buzzer confirms the probe has made proper contact. Two limits are worth stating plainly: thermal conductivity cannot separate diamond from moissanite — the dial groups them together — and Presidium states the instrument does not differentiate natural from synthetic coloured gemstones. Treat it as a fast screening and sorting tool that narrows the field before a laboratory report, not as a substitute for certification. It runs about three hours on two AA batteries, or off the supplied mains adaptor, and weighs 220 g.