EXPERIMENTAL HEAT TREATING OF TRAPICHELIKE BLUE SAPPHIRE OF SOUTHERN VIETNAM
Keywords:
Heat treatment, blue sapphire, trapiche, southern Vietnam, corundumAbstract
Twenty-seven rough trapiche-like blue sapphire samples from southern Vietnam were heat treated to investigate the effect of heat on their properties and to find the appropriate heat treatment schemes. In the heat treating experiments, the samples were divided into 2 batches. The first batch, consisting of 22 samples, was heated under an oxidizing condition to lighten the dark blue color of the samples, while the 5 samples in the second batch were heated under a reducing condition to intensify the blue color. The results show that heating at 1200oC can lighten the dark blue color and heating at 1400oC can change brown to blue colors. Heating the samples at a temperature higher than 1400oC can intensify the blue color in the samples. However, the trapiche appearance still persisted after the heat treatment. The UV-Vis-NIR absorption spectra of all samples exhibit Fe3+ absorption peaks, Fe2+/Ti4+ intervalence charge transfer (IVCT), and Fe2+/Fe3+ IVCT absorption bands. The more bluish color can be intensified after heating corresponding to the stronger intensity of Fe2+/Ti4+ and Fe2+/Fe3+ IVCT absorption bands. Chemical compositions reveal iron (Fe) and titanium (Ti) are the most significant minor and trace elements which affect colors in the studied samples. The high iron contents are related to the brown color especially in the dark tone of the brown color.
References
Abraham, J.S.D. (1982). Heat treating corundum: The Bangkok operation. Gems Gemol., 18(2):79-82.
Bgasheva, T.V., Ahmetshin, E.A., and Zharikov, E.V. (2012). Heat treatment enhancement of natural orange-red sapphires. Advances in Materials Science, 12(2):31-44.
Coldham, T. (1985). Sapphires from Australia. Gems Gemol., 21(3):130-146.
Emmett, J.L. and Douthit, T.R. (1993). Heat treating the sapphires of Rock Creek, Montana. Gems Gemol., 29(4):250-272.
Emmett, J.L., Scarratt, K., McClure, S.F., Moses, T., Douthit, T.R., Hughes, R., Novak, S., Shigley, J.E., Wang, W., Bordelon, O., and Kane, R.E. (2003). Beryllium diffusion of ruby and sapphire. Gems Gemol., 39(2):84-135.
Ferguson, J. and Fielding, P.E. (1971). The origins of the colours of yellow, green and blue sapphires. Chem. Phys. Lett., 10(3):262-265.
Ferguson, J. and Fielding, P.E. (1972). The origins of the colours of natural yellow, green, and blue sapphires. Aus. J. Chem., 25:1371-1385.
Fritsch, E. and Rossman, G.R. (1987). An update on color in gems. Part 1: introduction and colors caused by dispersed metal ions. Gems Gemol., 23(3):126-139.
Fritsch, E. and Rossman, G.R. (1988). An update on color in gems. Part 2: colors involving multiple atoms and color centres. Gems Gemol., 24(1):3-15.
Guo, J., Wang, F., and Yakoumelos, G. (1992). Notes and new techniques: sapphires from Changle in Shandong Province, China. Gems Gemol., 28(4):255-260.
Häger, T. (2001). High temperature treatment of natural corundum. Proceedings of the International Workshop on Material Characterization by Solid State Spectroscopy; April 4-10, 2001; Hanoi, Vietnam, p. 24-37.
Hughes, R.W. (1997). Ruby and Sapphire. RWH Publishing, Boulder, CO, USA, 511p.
Keller, A.S. and Keller, P.C. (1986). Notes and new techniques: the sapphires of Mingxi, Fujian Province, China. Gems Gemol., 22(1):41-45.
Khoi, N.N., Thuyet, N.T.M., Nam, N.V., and Duong, N.T. (2011). Three main types of corundum gem deposits in Vietnam. Proceedings of the International Gemmological Conference; July 14-17, 2011; Interlaken, Switzerland, p.102-105.
Khotchanin, K., Thanasuthipitak, P., and Thanasuthipitak, T. (2009). The structure and chemical composition of trapiche blue sapphire from southern Vietnam and Cambodia. J. Gemmol. Assoc. Hong Kong, 30:25-35.
Khotchanin, K., Thanasuthipitak, P., and Thanasuthipitak, T. (2010). Characteristics of trapiche blue sapphire from southern Vietnam. Chiang Mai J. Sci., 37(1):64-73.
Koivula, J.I., Kammering, R.C., and Fritsch, E. (1992). Gems News: Update on Vietnam gems. Gems Gemol., 28(4):274-275.
Li, J. (2006). The adverse impact of scatter on the tone of Shangdong Sapphire. Australian Gemmologist, 22(9):408-412.
Maxwell, M. (2002). The processing and heat treatment of Subera (Queensland) sapphire rough. Australian Gemmologist, 21(8):279-286.
McKague, H.L. (1964). Trapiche emeralds from Colombia. Gems Gemol., 11(7):210-213, 223.
Nassau, K. and Jackson, K.A. (1970). Trapiche emeralds from Chivor and Muzo, Colombia. Am. Mineral., 55(3-4):416-427.
Nassau, K. (1981). Heat treating ruby and sapphire: technical aspects. Gems Gemol., 17(3):121-131.
Nassau, K. (1994). Gemstone Enhancement, History, Science and State of the Art. 2nd ed. Butterworth- Heinemann, Oxford, UK, 252p.
Newman, R. (2000). Ruby, Sapphire & Emerald Buying Guide: How to Evaluate, Identify, Select and Care for These Gemstones. International Jewelry Publications, Los Angeles, CA, 164 p.
Schmetzer, K., Hänni, H.A., Bernhardt, H.J., and Schwarz, D. (1996). Trapiche rubies. Journal of Gemmology, 26(5):65-85.
Smith, C.P., Kammerling, R.C., Keller, A.S., Peretti, A., Scarratt, K.V., Khoa, N.D., and Repetto, S. (1995). Sapphires from southern Vietnam. Gems Gemol., 31(3):168-186.
Sunagawa, I., Bernhardt, H.J., and Schmetzer, K. (1999). Texture formation and element partitioning in trapiche ruby. J. Cryst. Growth., 206:322-330.
Suwa, Y. (1999). Gemstones Quality & Value: Vol. 1. Sekai Bunka Publishing Inc., Tokyo, Japan, 143p.
Themelis, T. (1992). The Heat Treatment of Ruby and Sapphire. 1st ed. Gemlab, Inc., Clearwater, FL, USA, 236p.
Tombs, G.A. (1982). Heat treatment of Australian blue sapphires. Z. Deut. Gemmol. Ges., 31:41-48.
Van Long, P., Quang Vinh, H., Garnier, V., Giuliani, G., Ohnenstetter, D., Lhomme, T., Schwarz, D., Fallick, A., Dubessy, J., and Trong Trinh, P. (2004). Gem corundum deposits in Vietnam. J. Gemmol., 29(3):129-147.
Vichit, P. (1987). Gemstones in Thailand. Journal of the Geological Society of Thailand, 9:108-133.
Wang, F. (1988). The sapphires of Penglai, Hainan Island, China. Gems Gemol., 24(3):155-160.
