Browsing by Author "Wijesuriya, G."

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    Enhancement of the Colour of Natural Greenish Yellow Chrysoberyl Using Heat Treatment Techniques
    (Uva Wellassa University of Sri Lanka, 2019) Ekanayaka, E.M.D.K.; Jaliya, R.G.C.; Wijesuriya, G.
    Sri Lanka is one of the greatest gem sources and trading place in the world and has a rich, almost unparalleled tradition and remains vitally important to the global gemstone market. Chrysoberyl (BeAl2O4) is a variety of gemstone which is predominantly greenish, yellow, yellowish green, brown or rarely green in colour. The most common colour of chrysoberyl in Sri Lanka is transparent greenish yellow which less appealing than the yellowish green colour. The exposure of a gem to high temperatures for the purpose of altering its colour and/or clarity was a common practice for centuries and research on chrysoberyl seldom carried out in Sri Lanka. Thus, the study based on heat treatment of chrysoberyl in order to enhance the colour and the clarity. 10 samples were collected from Ratnapura, Eheliyagoda and Rakwana area and samples were cut into two pieces along C axis (Optic axis) using a lapidary sawing machine. Heat treatment was done in both oxidizing and reducing atmospheric conditions and by varying the temperatures from 700 °C to 1200 °C, with the soaking time of 15 minutes to 2 hours. Untreated and treated stones were analyzed using Raman spectroscopy. Best colour and clarity enhancement were obtained when treating the stones under reducing atmosphere and greenish yellow colour chrysoberyls transformed into an apple green colour. Furthermore, with the increase in temperature, the colour change from greenish yellow to light green appeared more dominantly. In prospect of clarity during the heat treatment got enhanced the clarity by dissolving the colloidal impurities inside the stone. The greenish yellow chrysoberyl which has an unappealing colour could be converted into a more desirable green colour under reducing condition with the maximum temperature of 1200 °C. Raman spectroscopy has indicated peaks at 100 cm-1, 400 cm-1 due to OH bond stretching. Analyzing the Raman spectroscopy of the heat treated Chrysoberyl samples, some peaks got increase and some peaks got decrease significantly. Therefore, the Raman spectroscopy could use to identify the heated chrysoberyls from the unheated.
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    Identification of Heat Treated Natural Blue Spinel Using Raman Spectroscopy
    (Uva Wellassa University of Sri Lanka, 2019) de Silva, A.D.C.; Jaliya, R.G.C.; Wijesuriya, G.
    Sri Lanka is well known to the world for its vast potential of gem minerals. It is known in the ancient times as “Rathna Dhweepa”– “The Island of Gems”. Almost 75% of the landmass of Sri Lanka is composed of ancient gem-bearing rocks. Sri Lanka produces more than 75 species and varieties of gem minerals. The gem mineral Spinel is found in greater abundance in Sri Lanka as compared to other gem minerals. Most of the naturally occurring blue spinel is dark blue in color. These dark blue spinels have no demand and have a very low market price. Therefore, this study was focused on heat treatment of this low value material, under specific temperatures and atmospheric conditions for certain durations to reduce its color intensity, dissolve colloids and develop methods to identify treated stones from untreated natural stones. Samples of dark blue spinels were heat treated under both reducing and oxidizing atmospheric conditions at a temperature ranging from 600 °C to 1200 °C for 20 minutes to 2 hours. Both treated and untreated samples were then analyzed using Raman Spectroscopy. When the spinels were treated under reducing conditions no changes were observed. Color reduction and clarity enhancement were observed when the stones were treated under oxidizing atmosphere conditions. Dark blue spinel turned into greyish blue in colour with enhanced clarity. Heat treated spinels could be easily identified by Raman Spectroscopy by the width of the 405 m-2 Raman line. A wider and less intense peak could be observed for treated stones whereas in untreated stones a sharp peak of greater intensity could be observed. The results of this research have proved that dark blue spinels could be lightened and clarified by low temperature heat treatment and identification of treated stones from untreated stones could be done by analyzing through Raman Spectroscopy.
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    Investigation of the Use of Paddy Husk Silica as a Compound for Polishing Gem Minerals
    (Uva Wellassa University of Sri Lanka, 2019) Bandara, R.W.M.D.D.; Jaliya, R.G.C.; Wijesuriya, G.
    This research is focused on the use of paddy husk ash as a compound for the polishing purposes of gem materials. Most of the gemstones in the present day are polished by using diamond powder which often produces scratches and uneven surfaces on the facets on the surfaces on the facets owing to the greater hardness of the polishing medium which decreases the quality and value of the gemstones. Diamond is the hardest of all natural substances act as a cutting medium rather than a polishing medium. In this research, a spherical balls prepared by mixing paddy husk ash and cooked rice with an excess amount of water. This ball is eventually dried under the sun for four days. A special suspension medium was used to polish the gemstones with the paddy husk ash polishing agent. This polishing oil bonds the polishing powder to the polishing disk and retains the polishing powder intact during polishing. The polishing powder was embedded into a copper disk and was it used as the polishing plate. The silica based polishing paste were subjected to an XRF (X-ray Florescence) analysis to determine the elemental composition. XRF analysis shows that there were 92.1% of silica present as the major element. Remaining oxides are MgO, Al2O3, K2O, SO3, MnO and TiO2 presents as minor elements in the sample. XRD (X-ray Diffraction) analysis shows that the bulk of the sample is amorphous. FTIR (Fourier Transform Infrared Spectroscopy) shows that the O-H, Si-OH, H-O-H and Si-O-Si bonds in the sample. Optically flat surfaces were produced when a gemstones were polished using this compound. This polishing compound has proved to be an excellent product to polish species and varieties of gems. It is an ideal substitute for diamond powder which very costly and less effective.