![]() ![]() Heating at high temperatures will damage most inclusions in ruby and sapphire and is often detectable by trained gemologists. The border between high- and low-temperature heat treatment has been defined by Emmett (in Hughes et al., 2017) as the temperature needed to dissolve second-phase microcrystals, which is somewhere between 1200° and 1350☌. Various parameters such as temperature, heating and cooling time, and oxidizing or reducing atmosphere will affect the final color (Emmett and Douthit, 1993 Emmett et al., 2003 Hughes et al., 2017). Heat treatment has been used to improve the color and/or clarity of corundum for more than a thousand years. This study also showed that Fourier-transform infrared (FTIR) spectroscopy, specifically the peak at 3232 cm –1, is a useful technique to detect low-temperature heat treatment in pink sapphires from Madagascar. The results showed that the width decreased around 5 cm –1 after heating at 1000☌. We measured full width half maximum at ~976 cm –1 (ν 1, related to the PO 4 group of monazite) after all annealing steps. While the Raman spectra of zircon remained unchanged, except in the region of 1000 cm –1 after heating at 1000☌, the Raman peaks of monazite crystals became sharper with increasing temperature. Raman spectroscopy was used to detect the effect of heat treatment on zircon and monazite crystals. Interestingly, the monazite crystal inclusions changed color from orange-brown to near-colorless after heat treatment. Other common inclusions such as needles, particles, etch tubes, and mica and zircon crystals remained unaffected. ![]() Only slight alterations of monazite inclusions and iron stains in fissures were observed following these heating conditions. This study showed that after heat treatment at 800✬, a subtle blue tint was removed, making the color a purer pink. Therefore, characterizing Madagascan pink sapphire before and after heat treatment helps laboratories develop criteria for treatment detection. ![]() ![]() Pink sapphires from Madagascar, one of the most important sapphire-producing countries, are no exception. Low-temperature heat treatment is often applied to gem corundum to improve its appearance. Photo by Robert Weldon/GIA courtesy of Jeff Hapeman, Earth’s Treasury. From top to bottom, they weigh 1.16 ct, 1.17 ct, and 1.06 ct. These pink sapphires from Ilakaka, Madagascar, underwent low-temperature heat treatment. Comprehensive CAD/CAM For Jewelry Certificateįigure 1. ![]()
0 Comments
Leave a Reply. |