Assessing Color of Gemstones

A precise and shared description of gemstones color could greatly help their classification and market evaluation, and the key to develop an efficient color evaluation system for gemstones is the creation of a common descriptive language and assessment method. Nowadays, there is a lack of standards for the determination of color of gemstones and traditional color assessment is exclusively based on the direct visual observation, in some cases with lenses and microscopes. The underlying problem is that light impinging gemstones, due to their physical characteristics, produces scattering and multiple reflecting phenomena. This puts the process of gemstone color assessment out of the scope of classic colorimetry. What needs to be assessed is the overall appearance of the gemstone and this explain why, so far, it is realized mainly by visual inspection. In this work, we investigate the relationship between the use of color measuring instruments and the visual inspection method, for the determination of gems color appearance. We set up a perceptual experiment involving 21 participants to correlate the measured and the perceived colors of a set of gemological samples. Results report the correlations between instrumental measures and the visual assessment of gemstones color appearance and can be a potential base for a future standard method for gemstones color assessment.