corundum, properties.3, gems

The Gemtek Gemmologist is evaluated as a thermal probe intended to distinguish not only diamond from its simulants but also gemstones with much smaller differences in thermal response. The report questions the customary description of such instruments as thermal conductivity testers, noting evidence that their responses relate to thermal inertia. The Gemmologist measures the time taken for its heated probe tip to cool between two predetermined temperatures after contact with a specimen, converting this interval into a digital count; lower readings indicate more rapid heat transfer. Reliable operation requires calibration for the working environment, a restricted ambient temperature range, specimens warmed to near body temperature, and consistent perpendicular probe contact and pressure. Tests were conducted after calibration, with specimens initially warmed against the wrist and measured ten times in succession. Most stones weighed between 0.75 and 4 ct, and supplementary tests across a wider size range indicated no size effect under the conditions examined. Results demonstrated separation of ruby from garnet, aquamarine from blue spinel and topaz, and sapphire from blue tourmaline. The natural emerald and Gilson flux-grown synthetic emerald tested also gave clearly different readings. However, many materials produced overlapping ranges, reflecting both similar thermal properties and limited repeatability. The manufacturer’s suggestion that heat-treated stones should read 10–15 points higher than untreated stones could not be confirmed with the available samples. Specimen temperature proved especially important for materials of medium or low thermal conductivity: garnet and cubic zirconia gave substantially lower readings at room temperature than at body temperature, while insufficiently warmed corundum could produce readings within the diamond range. Diamond and the metals tested were comparatively insensitive to this temperature difference. Construction and operating procedures are described, including the spring-loaded probe, indicator lamps, audible signal and user-accessible calibration adjustments. The instrument is judged capable of supplying useful supplementary identification data, particularly for diamond, its simulants and small mounted stones inaccessible to conventional optical measurements. For gemstones within its measurable range, the standard refractometer offers greater precision. The report concludes that the Gemmologist’s demanding operating conditions can produce misleading results for inexperienced users, despite its intended accessibility to people with limited gemmological knowledge.