Instructions for a Gem Tester

Loose diamonds next to a jeweler's loupe ready to be tested

If you are in the business of selling and buying jewelry, it is imperative that you be able to distinguish between real diamonds and simulants and between gemstones and glass.



Gem testers work on the principle of heat conductivity. Diamonds conduct heat better than any known material. Therefore, a gem tester is internally calibrated to measure the heat conductivity of diamonds and other gems, each with distinctive heat conductivity.

Things You'll Need

• Calibrated gem tester
• Lint-free, chemical-free cloth
• Mild detergent
• Paper towels
• Water

Instructions

1. Clean the gemstone to be tested. Dunk it in warm, soapy water, using mild detergent. Do not leave the gemstone soaking in the water for more than a few seconds. Most gemstones on the market today have treatments to enhance color, and some treatments can be affected if left in water too long.

2. Dry the gemstone thoroughly with a paper towel or lint-free cloth. Ensure the gemstone surface to be tested is dry and clean with no fingerprints that could contain oily residue. Do not use chemicals to clean or dry gemstones to be tested, as any residue could cause the gem tester to give an inaccurate reading.

3. Turn on the gem tester. If batteries are being used, instead of electrical power through the included adaptor, ensure that there is enough power in the unit to perform an accurate test. Allow the unit to warm up for a minimum of 20 seconds.

4. Uncap the heat probe "pen" carefully, and hold the probe point gently but firmly on the surface of the gemstone to be tested. If it is a diamond, be sure to gently depress the probe point entirely into the pen. Hold the probe in place until the indicator needle on the gem tester scale stops moving.

5. Read the gem tester scale to determine the type of gemstone being tested. Make note of the reading obtained. Turn the unit off unless you will be testing other stones. Repeat Steps 1 through 5.

6. Carefully inspect the heat probe "pen" tip. If it has lint or debris after testing, wipe carefully with a lint-free cloth. Do not use any liquid to wipe it off. Carefully replace the probe pen cap.

Tips & Warnings

• Make sure the gem tester is properly calibrated. Follow the manufacturer's instructions to verify calibration. If you don't have calibration instructions, test a gemstone you know to be real to verify the unit is working properly before testing a gemstone of unknown composition.

• Each time you test a gemstone with the thermal probe, the gemstone's temperature rises. Therefore, accurate test results should be obtained only by allowing the stone to return to room temperature prior to each probe.

• A gem tester can be used to identify mounted or loose stones. Just be sure to keep the heat probe squarely on the gemstone in question, not on the metal prongs or findings.

• The gem tester probe tip can be easily damaged, so handle the probe with care and take care not to inadvertently bend it, especially when replacing the protective cap.

• Certain gemstone treatments can interfere with the accuracy of a heat conductivity gem tester.

• The heat conductivity of diamonds and Moissanite is relatively close, so gem testers are not a reliable means to differentiate the two gemstones. Visual inspection under a jeweler's loupe is the best way to distinguish Moissanite from diamonds.

References

• Star Struck, LLC: Presidium Gem Tester User Handbook
• Gemologyonline.com: How Accurate Is the Presidium Gem Tester?
• Gemworld International, Inc.: Moissanite Detection