![]() Heat-treatment temperatures were pushed higher as furnace technology improved with the advent of electricity, reaching temperatures of 1500°–1800☌ (corundum melts at 2040☌). With ruby and sapphire, records of heat treatment go back more than a thousand years (Al-Beruni, 1989). Raman analysis of calcite and spinel inclusions also proved valuable in providing complementary evidence of low-temperature heat treatment.ĭue to the value and rarity of fine gems, early pioneers developed techniques to treat lower-quality material, including fracture filling and heat treatment. Microscopic examination provided useful visual indications of heat treatment, even at lower temperatures. Many of those were found to be sensitive to heat treatment with regard to morphology and phase transition their reactions varied depending on a number of factors such as size, distance from the surface, and species. The samples were documented using macrophotography, photomicrography of inclusions, ultraviolet fluorescence imaging, and spectroscopic analysis (Raman, ultraviolet/visible/near-infrared, and infrared) to record any changes, with a focus on features that could help detect heat treatment.Ī wide variety of solid inclusions, including calcite, mica, spinel, and zircon, were found in Mogok ruby. ![]() In this study, the authors heated Burmese ruby samples from Mogok, Myanmar, at temperatures ranging from 600° to 1500☌. ![]() ABSTRACTĭetection of heat treatment below 1200☌ in ruby and sapphire can present challenges to gemologists, as alterations to the material are often subtle. Photo by Wimon Manorotkul faceted ruby courtesy of Kiarttichatra Intarungsee. The striking appearance of Mogok ruby is highly sought after. A faceted heated ruby from Mogok, Myanmar, weighing more than 3 ct, stands out against a backdrop of untreated ruby rough from the same origin. Comprehensive CAD/CAM For Jewelry Certificateįigure 1.
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