corundum, properties.3, gems

The Alpha-Test electronic gemstone identifier is evaluated as a thermal-probe instrument capable of assisting identification of diamonds, diamond simulants and selected coloured gemstones. Its operation is compared with that of the earlier Gemtek Gemmologist. Both instruments measure the time taken for a heated probe tip to cool between two predetermined temperatures after contact with a gemstone; lower readings indicate faster heat removal. Because thermal differences among non-diamond materials are comparatively small, repeatable measurements require a draught-free environment at 18–25 °C, a stone first warmed to body temperature, and controlled probe pressure with the tip perpendicular to the tested surface. The Alpha-Test simplifies operation through automatic display resetting and thermostatic regulation of probe temperature, with a ready indicator and an off-scale warning above its maximum numerical reading of 999. Separate sapphire and emerald calibration adjustments provide two-point calibration across the measuring range. A permanently attached probe is identified as a servicing disadvantage because damage would require returning the complete instrument. Following calibration with sapphire and natural emerald, Read tested each specimen ten times and recorded average readings and their spread. Repeatability was better for materials with higher thermal conductivity: diamond, corundum, topaz, high zircon and spinel showed relatively narrow spreads, whereas lower-conductivity materials produced substantially wider variation. The author stresses that repeat measurements on one specimen do not represent the full range expected among different stones of the same species. The instrument is considered particularly useful for diamonds and their simulants, and for very small mounted coloured stones that cannot readily be examined with a refractometer or reflectivity meter. With care, useful separations include ruby from garnet, sapphire from tourmaline, and natural emerald from some flux-grown synthetic emeralds. Natural and synthetic spinel give appreciably different readings, while high and low zircon differ markedly. However, readings for topaz, high zircon and natural spinel overlap too closely for reliable differentiation. The report therefore presents thermal testing as a practical supplementary method whose value depends on controlled operating conditions and sufficient separation between the thermal responses of the materials under consideration.