How to use a Presidium gem tester to identify diamonds and gemstones
The gem tester can be powered by battery or AC adapter. Insert the probe pen into the socket at the side of the tester machine and switch the unit on. A simulant test disc on the machine can be used to ensure the tester is functioning correctly and is ready to go.
Make sure the gemstone you are testing is clean and dry. Clean it by lifting carefully with tweezers and rubbing it on to a tissue or clean cloth. Ensure the gemstone is at room temperature (or between 18 and 27 degrees).
Hold mounted jewellery in one hand and the tester pen in the other hand. Place loose gemstones on the metal stone rest, securing it with one hand while holding the probe pen in the other.
Gently place the probe pen's retractable tip against the gemstone. Apply light pressure so the tip fully compresses into the probe pen. For accurate results, make sure the probe tip is held at a right angle or is perpendicular to the gemstone face. A warning signal will sound if the pen comes into contact with a metal mount.
After around two seconds, the reader on the machine's LED screen will reach its highest position, then will fall back down. The reading should be taken at the highest position.
How to read a Presidium gem tester
Presidium gem testers have a specially calibrated, semi-circular dial that shows the heat conductivity of the stone. The display will have two zones, one smaller green section and a larger red section. If the indicator dial stops in the green zone, the gemstone is diamond or moissanite. If the needle reaches its top point within the red band, a simulant has been identified. A number of simulant options may be revealed during the reading, but the machine will help to distinguish between, among many others, emerald and jadeite, topaz and citrine, and topaz and aquamarine.
Several models of Presidium gem tester are available at Maddisons of Durham including the Presidium Diamond Mate Pocket Tester, the Digital Gem Indicator for Coloured Gemstones and the Presidium Duo Tester II, which identifies diamonds and gemstones based on two different testing methods. Not only does it assess thermal conductivity, it also evaluates reflective indexes too, giving accurate results both indoors and out.