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«“√ “√ √“™∫— ≥±‘µ¬ ∂“π ªï ∑’Ë Ú˜ ©∫— ∫∑’Ë Û °.§.-°.¬. ÚıÙı Sakda Siripant ˜Û˘ One of the most important challenges facing gem dealers is how to grade rubies into various categories. The most important problem in trying to develop an effective ruby-grading termino- logy is the lack of understanding among gem dealers about color terminology as used by color sci- entists. As a matter of fact, the principal difference between a fine ruby and a lower graded stone is the color saturation or chroma and intensity of the hue (dominant color) rather than a color or hue shift. (Fig. 1) The Gem and Jewelry Insti- tute of Thailand (GIT) in coopera- tion with the Thai Gem and Jew- elry Traders Association (TGJTA) has decided that Thailand, as the world’s largest exporter of rubies, should have an efficient and inter- nationally recognized grading sys- tem that satisfies both traders and the Tourism Authority of Thai- land. Thus, a working committee of academicians from GIT and gem traders from the TGJTA was established. This committee then created a ruby grading system. The working committee held more than 10 meetings between October 2000 and October 2001, and the results of their extensive work follows: Methods used for ruby grading and results In general there are three fac- tors governing the assessment of a ruby. Its beauty, quality and value (natural or synthetic origin). (See the flowchart showing criteria used to assess a ruby’s grading; Diagram 1). 1. Beauty This is the most important easily seen aspect of a gemstone and a strong factor in de- termining its value. Beauty is sub- jective. In fact, the word “beauty” is a collective term; with regard to assessing a ruby or, for that matter, any gemstone, the term combines the concepts of color, brilliance and transparency. 1.1 The attractive color of a ruby usually depends on personal taste. The key to its attractive color is not merely the gemstone’s simple two-dimensional color, but the bal- ance of light and dark tones in a mosaic-like pattern that gives the gem a wonderful three-dimen- sional appearance. This is the ef- fect of reflection and refraction caused by good and proper faceting. 1.2 The brilliance of a ruby is caused by light refracted and re- flected from a properly faceted gem. As the brilliance increases, rubies become more valuable. (Fig. 2) 1.3 Transparency and the lack of inclusions and blemishes combined with its brilliance are what make a ruby so beautiful. (Fig. 3) Three criteria, attractive color, brilliance, and transparency, were used by GIT to select eight sets of standard rubies weighing from 0.75 to 1 carat from four different geographic regions. Included were two sets of Thai, Mogok, Mong Hsu andMadagascar rubies. Each set has five tone levels rang- ing from dark to light. (Fig. 4) These standard ruby sets were used to conduct the color prefer- ence survey. The participants in Fig. 1 Fig. 3 Fig. 2