corundum, Madagascar.12, gems

gems, corundum, treatments.6, Burma.12, ruby, Mong Hsu, heat treatment

Mong Hsu rubies have been heat treated in air at 1100, 1200, 1300, 1400, 1500, and 1600 °C, with their visual appearance and surface composition (via XPS) monitored at each stage. The distinctive blue cores seen in untreated stones begin to fade at 1100 °C and vanish completely above 1500 °C. Initially, trace Na, Ca, Si, and Fe were detected on untreated surfaces, while Ti first appeared after heating to 1100 °C. Surface concentration plots show peak Fe at 1300 °C, and Ti peaks near 1300 and 1500 °C. These changes indicate that both the oxidation of Fe²⁺ to Fe³⁺ and the temperature-dependent diffusion of Fe and Ti ions reduce Fe²⁺–Ti⁴⁺ charge transfer, driving the observed color change.

gems, jade, jadeite, fei cui, Mesoamerica, Mexico, Guatemala, Costa Rica, Mayans, Olmecs, Aztecs, archaeology, history, archaeogemology

corundum, Thailand.12, gems

corundum, Malawi.12, gems

corundum, treatments.6, gems

Blue color enhancement of sapphire by surface-diffusion processes at high temperatures has been reported since the 1980s. However, most treatment processes are based on “trial and error.” In this article, the diffusion coefficients of Fe and Ti ions in sapphire crystals calculated during various treatment conditions are presented. Colorless and light blue sapphires were treated with (unspecified) Fe- and Ti-containing chemicals in an aluminum oxide crucible at a temperature of 1,800–1,900 °C for up to 72 hours at a Thai jewelry company. The thickness of the diffusion layer was measured from samples cut into 0.8 mm thick plates. The concentrations of Fe and Ti in different layers, starting from the outer surface of the samples, were determined by electron-microprobe analysis. The diffusion coefficients of Fe and Ti in sapphire are mainly controlled by temperature, duration of the treatment, thickness of the diffused layer, and the initial concentrations of Fe²⁺ and Ti⁴⁺ ions in the chemical additives. However, at certain temperatures, the diffusion coefficients of Fe and Ti ions were essentially constant, regardless of variations in the duration. The diffusion coefficient of Ti ions was much greater than that of Fe ions, being 6.57 × 10⁻⁹ cm²·s⁻¹ and 1.62 × 10⁻⁹ cm²·s⁻¹, respectively. Using these coefficients in conjunction with specified temperatures and duration times, it is possible to control the thickness of the diffusion layer in sapphire. These coefficients may also be useful toward lightening dark-colored sapphires, such as those from Shandong, China.

corundum, Laos.12, gems

corundum, Tajikistan.12, spinel, gems

corundum, Burma.12, quality.10, gems

gems, corundum, History.1, archaeology, archaeogemology, Central Asia, Afghanistan, corundum, ruby, Ai Khanoum, Greek, Kushan, Iran

Presented here is the publication of a great many objects from the Indo-Iranian borderlands, dating primarily from the period between the Greeks and the Kushans, but more broadly covering the entire pre-Islamic history of the region. Especially well represented are coins and Buddhist representations from India or Afghanistan. The illustrations are of very high quality. Priority is given to the object entries over the accompanying texts, which are concise and written by leading specialists, ranging from “The Civilization of Central Asia in the Bronze and Iron Ages” (H.-P. Francfort) to “Christianity in Herat” (Ph. Gignoux), including “Indo-Greeks, Indo-Scythians, Indo-Parthians” (O. Bopearachchi) and “The Coinage of the ‘Iranian Huns.’” Contains ruby and two diamonds in ring from Ai Khanoum.