Development of Green Colour in Topaz Using Diffusion Method

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dc.contributor.authorShamal, Y.P.N.
dc.contributor.authorJaliya, R.G.C.
dc.date.accessioned2022-10-05T05:54:07Z
dc.date.available2022-10-05T05:54:07Z
dc.date.issued2021
dc.description.abstractTopaz is one of the abundant gem varieties in Sri Lanka with the chemical formula of Al2SiO4(F, OH)2, which has a hardness of 8 on the Moh’s hardness scale. The colourless Topaz varieties have less market value compared to the coloured Topaz varieties. Irradiation and other methods are used traditionally to improve the appearance of Topaz. Nevertheless, conventional methods have drawbacks such as high manufacturing cost, less operational safety due to radioactivity related processes. Hence, the present study tested the diffusion effect of Chromium (II) chloride on colourless topaz with the aid of heat treatment. Seventy-two colourless Topaz samples were treated with Chromium (II) chloride. The selected stones were heated under reduced and oxidizing conditions with the Chromium (II) chloride at different temperatures (600 0C, 700 0C, 800 0C, and 900 0C ) and different soaking times (1, 2, and 3 hours). In both reduced and oxidizing conditions Chromium (II) chloride, diffused into the topaz by producing a shade of pale green to dark green colour. Colour shade becomes strong with the increase of the temperature. Produced colours created a desirable appearance on the stones. At 900 0C the produced green colour was identified as ‘GB/BG 7/2’ in the GIA colour grading system. The durability of the coating was tested for acidic conditions (with HNO3 and H2SO4 acids) and sonication. The produced surface coating was stable under acidic conditions as well as under the sonication. Oxidizing conditions in electrically operated furnace is economically beneficial over gas furnace in producing colours. Finally, colourless Topaz could develop the green colour by diffusion with the optimum temperature of 900 0C with the soaking time of 1 hour under oxidizing conditions. Keywords: Diffusion Treatment; Topaz Enhancement; Colour development of gemstonesen_US
dc.identifier.isbn978-624-5856-04-6
dc.identifier.urihttp://www.erepo.lib.uwu.ac.lk/bitstream/handle/123456789/9736/Page%20300%20-%20IRCUWU2021%20-%20150%20-%20Y.P.N.%20Shamal%20-%20Development%20of%20Green%20Colour%20in%20Topaz%20using%20Diffusion%20Method.pdf?sequence=1&isAllowed=y
dc.language.isoenen_US
dc.publisherUva Wellassa University of Sri Lankaen_US
dc.subjectMineral Sciencesen_US
dc.subjectMaterials Sciencesen_US
dc.subjectGemstonesen_US
dc.subjectApplied Earth Sciencesen_US
dc.subjectGeochemistryen_US
dc.titleDevelopment of Green Colour in Topaz Using Diffusion Methoden_US
dc.title.alternativeInternational Research Conference 2021en_US
dc.typeOtheren_US
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