Ruby And Sapphire Quality Grading

Till today there are no consensus on grading rubies and sapphires. The reasons may be political, geographical and other technical factors. There is love/hate relationship among gem dealers and lab gemologists and it will be there forever. No one has done research on the side effects of color graders from short/long term use of soft drugs, medical status, color blindness/defectiveness, color descriptions and perceptions in various languages and much more. The common belief is it is better to have an imperfect system than no system at all.

Wilawan Atichat, Visut Pisutha Arnond, Sakrapee Saejoo, Chotima Kunwisutpan, Boontawee Sriprasert and Chakkaphant Sutthirat writes:

Grading systems for color, clarity and cut have been developed by the Gem and Jewelry Institute of Thailand Gem Testing Laboratory (GIT-GTL) to improve the overall quality grading of ruby and sapphire from various global sources. These quality grading systems are used for communication in the gem and jewelry trades in Thailand and Japan (currently for ruby).This ongoing research has been expanded from the ruby and sapphire grading systems previously established by GIT-GTL.

Ruby and sapphire quality factors were determined from the results of a questionnaire that was given to gem traders in Thailand. These data were then used as a basis to establish eight preliminary sets of master stones that included ruby and various sapphires (blue, orange pink, purple, pink, orange, yellow, and green). Each set contained 15 stones of varying quality. These master stone sets were then sent to gem traders to solicit opinions. The outcome data were then integrated into the color, clarity, and cut grading systems. Eight final standard (master stone) sets were then developed, composed of 25 oval shaped, 0.75ct stones covering five quality grades (Excellent, Very good, Good, Fair, and Poor).

For color grading, the stones were placed 15-25cm from the standard light source (Macbeth 5000 K with an intensity of 1200 lux), and were visually graded face-up at a distance of 30cm and viewed perpendicular to the table surface. The hue, tone, and saturation of the stones were considered: dispersion and scintillation were excluded.

For clarity grading a Dialite Flip light source was positioned to the side of the stones (1cm away), which were placed on a dark background and graded using a 10x loupe. For confirmation purposes, the clarity of the stones was graded again with the unaided eye at 30cm distance (and 15-20cm from the light source) in the face-up position against a white background. The clarity grading was evaluated by using the GIT-GTL scoring system. As for the cut grading, factors for brilliance, face-up proportions, profile proportions, and finish were taken into consideration. The overall quality grading was usually peformed by at least three experienced gemologists.

The final evaluation of these corundum standard sets by gem traders in Thailand revealed that they are generally compatible with the quality grading being used in the trade. GIT-GTL is currently using these master stone sets for ruby/sapphire grading for some clients in Thailand and Japan.