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The Journal of the Royal Institute of Thailand Vol. 27 No. 3 Jul.-Sept. 2002 A Ruby Grading System ˜Û¯ A Ruby Grading System Set up by the Gem and Jewelry Institute of Thailand (GIT) for the Gemstone Industry + * Sakda Siripant Fellow, the Academy of Science, the Royal Institute + GIT Academicians: 1. Prof. Sakda Siripant, 2. Assoc. Prof. Dr. Visuth Pisutha-Arnond, 3. Dr. Pornsawat Wathanakul, 4. Ms. Wilawan Adichart, 5. Dr. Phongchan Chanthayos, 6. Mr. Thanong Leelawattanasuk, 7. Mr. Yongyut Khankaew, and 8. Mr. Sutas Singhabumrung. Thai Gem and Jewelry Trader Association Representatives: 1. Mr. Pornsert Sriorathaikul, 2. Mr. Porkuang sae Tang, 3. Mr. Pittiya Tiasuwan, 4. Mr. Chirayuth Vajanathavornchai, 5. Mr. Vichian Veerasaksri, 6. Ms. Chanida Chairanant, 7. Mr. Parks Satienrapat, 8. Ms. Nippaporn Amorpongchai, 9. Mr. Narain Suradejvibul, 10. Mr. Mohan Sachdeva, 11. Mr. Achakij Nawawatanasub, 12. Mr. Montree Udomrattanamanee, 13. Ms. Janet Ann Russell, 14. Mr. Somkiat Weerawuttiwong, and 15. Mr. Pongphan Tunyakijja. * Paper presented at the Academy of Science, The Royal Institute, February 6, 2002. The beauty of rubies is a combination of their attractive color, brilliance and transparency. These factors were the fundamental criteria used to select standard ruby sets. Two sets each of Thai, Mogok, Mong Hsu and Madagascar rubies were obtained. Each set was carefully selected so that each had five red color levels varying from dark to light; these were now considered standard sets. Each stone has a color code based on the Munsell system (hue value/chroma), including a specific color name. An extensive research effort regarding the subjective ruby color preferences of Thais, Japanese, Americans, Europeans and Indians was conducted. The result was that people from different countries expressed different preferences regarding hue, tone and color saturation. In order to effectively evalu- ate the most important factors (color, brilliance and transparency) that contribute to the beauty of ru- bies, a quantitative approach under the heading quality was used. The quality grading of a ruby de- pends on four independent criteria, namely, color grading, clarity grading, cut grading and carat weight. Color notations used in color grading are dark red (5R 2/8) deep red (5R 3/10), vivid red (2.5R 4/14) strong red (5R 4/12) pinkish red (8.75R 4/12) and purplish red (7.5RP 5/8). Clarity gradings are excellent (minute inclusions), fine (minor inclusions), very good (noticeable inclusions), good (moderate inclu- sions) and fair (significant inclusions). The cutting gradings are excellent, fine, very good, good, and fair. First, it must be determined whether the gemstone is of natural or synthetic origin. This is a two- stage procedure. Second, it must be determined whether the gemstone’s color and clarity are natural or have been altered artificially. Key words : ruby grading, color grading of a gemstone, quality level of ruby, ruby standard