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The Journal of the Royal Institute of Thailand Vol. 27 No. 3 Jul.-Sept. 2002 A Ruby Grading System ˜ÙÚ in the following tables. (Fig. 5-8) In order to evaluate three of the important factors contributing to the beauty of a ruby more pre- cisely we used quantitative meth- ods grouped under the heading “Quality”. 2. Quality The quality of a ruby is based on four independent criteria: color, clarity, cut grading and carat weight. 2.1 Color grading The color of a ruby determines at least 50 per cent of its final market value. The color grading of rubies is very difficult and more subjec- tive than the grading of diamonds. The GIT method has been de- signed to provide a meaningful grading system that is easily under- stood and used. This system can be directly related to market prices. The color grading of a ruby be- comes complicated because three separate components that are both independent and interrelated, namely hue, tone, and saturation (color intensity). Hue describes the domi- nant and additional colors in a gemstone that are visible to the naked eye. In our example, a pur- plish/red (PR) ruby has red as the dominant color and purple as the secondary color. Value or tone -This refers to the lightness or darkness of a color sensation. Saturation or chroma is best described as the strength or intensity of the hue sensation. The GIT Color Grading System is based on the Munsell Color Chart. Each ruby was matched to the appropriateMunsell color chip and viewed under a standard 5,000 -degree Kelvin light source (1,500 lux illuminant). Each stone in the standard sets was assigned a Munsell color code and name. The results were compared with the ISCC-NBS of Janpanese prefer Burmese (Mogok) rubies, accord- ing to a sample test of 55 persons. Thai ruby (40%) Mong Hsu ruby (27%) Mogok ruby (49%) Madagascar ruby (27%) Fig. 8 Fig. 9 Color matching between a ruby and a Munsell color chip. Fig. 11 Sample of rubies with Munsell color codes and names. Fig. 10 Munsell color charts.