Diamond is an extremely effective thermal conductor and usually an electrical insulator. The former property is widely exploited in the use of an electronic thermal probe to separate diamonds from their imitations. These probes consist of a pair of battery-powered thermistors mounted in a fine copper tip. One thermistor functions as a heating device while the other measures the temperature of the copper tip: if the stone being tested is a diamond, it will conduct the tip's thermal energy rapidly enough to produce a measurable temperature drop. As most simulants are thermal insulators, the thermistor's heat will not be conducted. This test takes about 2–3 seconds. The only possible exception is moissanite, which has a thermal conductivity similar to diamond: older probes can be fooled by moissanite, but newer Thermal and Electrical Conductivity testers are sophisticated enough to differentiate the two materials. Latest development is nano diamond coating, a nano layer of diamond material. If not tested properly it may show the same characteristics as a diamond Diamond Testing.
A diamond's electrical conductance is only relevant to blue or gray-blue stones, because the interstitial boron responsible for their color also makes them semiconductors. Thus a suspected blue diamond can be affirmed if it completes an electric circuit successfully.
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