Heat treatment of Corundum from Barra Velha Region, SC
DOI:
https://doi.org/10.22456/1807-9806.135817Keywords:
rubi, coríndon, tratamento térmico, gemologia, barra velhaAbstract
Ruby is the variety of corundum with the highest commercial value due to its intense red color caused by the presence of chromium in its chemical composition. The most valuable rubies are pure red, without secondary shades of pink or orange. Due to the rarity of high-quality gemstones, the gem industry has developed various treatment techniques to enhance the appearance and quality of gems, making them more attractive and valuable. Gem treatments are essential to provide quality gems to a broader market. Controlled heating of gems improves the color and transparency of various gem minerals, including ruby, sapphire, and topaz. This form of treatment is widely accepted in the international market. Since discovering the factors that cause color change in minerals, technological advancements have enhanced treatment methods to adhere to certain conditions to make the results increasingly predictable and stable. Originating from the Barra Velha deposits in Santa Catarina, Brazil, these rubies are characterized as low-quality stones. This study aimed to evaluate whether heat treatment of this material could offer the potential for these gems to be included in the national context of producing quality rubies. The treatment was performed on 10 ruby samples in an electric furnace at temperatures of up to 1600°C with controlled heating, cooling rates, and atmosphere to create a unique set of parameters for all treated samples and achieve stable conditions for the creation of crystal defects, oxygen diffusion in the crystal structure, and changes in charge compensation. In addition to conventional thermal treatment, flux healing was performed on two samples, which changed the color and improved the crystals' transparency. The change in color and improvement in the gemological quality of the crystals is visually identified by changes in light absorption patterns quantified through spectrophotometer analysis.
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