Color Enhancement of Natural Sapphires by High Pressure High Temperature Process

  • Song, Jeongho (Department of Materials Science and Engineering, University of Seoul) ;
  • Noh, Yunyoung (Department of Materials Science and Engineering, University of Seoul) ;
  • Song, Ohsung (Department of Materials Science and Engineering, University of Seoul)
  • Received : 2014.12.02
  • Accepted : 2015.02.02
  • Published : 2015.03.31


We employed the high-pressure high temperature (HPHT) process to enhance the colors of natural sapphires to obtain a vivid blue. First, we analyze the content of the coloring agent $Fe_2O_3$ using the wavelength dispersive X-ray fluorescence (WD-XRF) method. The HPHT procedure operates under 1 GPa at various temperatures of 1700, 1750, and $1800^{\circ}C$ for 5 minutes using a cubic press. We determine the color changes using the optical microscopic images, UV-VIS near-infrared (NIR) spectra, micro-Raman spectra, and Fourier transform-infrared (FT-IR) spectra for all sapphire samples before and after the treatment. The optical microscopic results indicate that the HPHT process can enhance the sapphire color to a vivid blue at temperatures above $1750^{\circ}C$. The UV-VIS-NIR spectra identify the color changes explicitly and quantitatively through providing the Lab color scales and color differences. Both results demonstrate that the colors of natural sapphires can be enhanced to a vivid blue using the HPHT process above $1750^{\circ}C$ under 1 GPa for 5 minutes.


Sapphire;Color enhancement;HPHT;WD-XRF;FT-IR


Supported by : National Research Foundation of Korea (NRF)


  1. Y. Chiang, D. Birnielll, and W. Kingery, Physical Ceramics; pp. 133-35, John Wiley & Sons Inc., Canada, 1996.
  2. Y. K. Ahn, "Color Change by the Beryllium Diffused and Heat Treated Corundum from Various Deposits," pp. 48-58, Ph. D. Thesis, Hanyang University, Seoul, 2013.
  3. T. Themelis, Beryllium-Treated Rubies & Sapphires; pp. 6-7, A&T Publishing, LA, 2003.
  4. S. F. McClure and C. P. Smith, "Gemstone Enhancement and Detection in the 1990s," Gems Gemol., 36 [4] 337-38 (2000).
  5. R. E. Kane, R. C. Kammerling, and J. I. Koivula, "The Identification of Blue Diffusion-Treated Sapphires," Gems Gemol., 26 [2] 115-33 (1990).
  6. K. Chemetzer, H. A. Hanni, E. P. Jegge, and E. J. Chupp, "Dyed Natural Corundum as a Ruby Imitation," Gems Gemol., 28 [2] 112-15 (1992).
  7. J. H. Song, S. H. Moon, G. W. Jang, and O. S. Song, "Property Change of Sri-Lanka Milky Geudas with Heat Treatment," J. Korean Gems and Jewelry, 7 [3] 129-36 (2013).
  8. J. H. Song and O. S. Song, "Color Enhancement of the TypeII and TypeIaB Brown Diamonds into Colorless by HPHT Process(in Korean)," J. Korean Ceram. Soc., 49 [3] 221-24 (2012).
  9. J. H. Song and O. S. Song, "Surface Graphite Formation of the Brown Colored Type I Diamonds During High Pressure Annealing(in Korean)," J. Korean Ceram. Soc., 49 [6] 614-19 (2012).
  10. E. Fritsch and G. R. Rossman, "An Update on Color in Gems. Part 3:Colors Caused by Band Gap and Physical Phenomena," Gems Gemol., 24 [2] 81-102 (1998).
  11. L. V. Nikolskaya, V. M. Terekhova, M. I. Samoilovich, "On the Origin of Natural Sapphire Color," Phys. Chem. Minerals, 3 213-24 (1978).
  12. M. Kadleikova, J. Breza, and M. Vesely, "Raman Spectra of Synthetic Sapphire," Microelectron. J., 32 955-58 (2001).