Traditionally, color grading at gemological laboratories is carried out by the human eye. A gemologist will line up a master-set of diamonds (featuring a D to Z color) to which the diamond’s color is compared to. The master-set of stones and the diamond are placed on a dull white countertop. The master-set is lined up with lightest (the top color) first, becoming progressively darker. The diamond’s color is then compared to the color of each stone of the master-set until the grader perceives its color to be the same.
Several problems arise when a human observer grades a diamond: every eye has a different "color deficiency". This means that every grader has deficiencies for certain colors. Further, the color and intensity of illumination influences the eye’s perception. This results in deviations in color grading of large (a few carats) and small diamonds (a few tens of points) as most master-sets feature diamonds of around one carat in size. Finally, larger labs will use two different master-sets with inevitably slightly different colors. As such, color grading within the same lab or between its branches may vary.
International Diamond Laboratories has developed ground-breaking technology enabling diamond color grading to be executed to an exact standard. It is not based upon the personal perception of a grader and a non-regulated set of master stones, but the result of an automated process. The International Diamond Laboratories Color MeterTM determines the precise color value of a diamond with accuracy far above existing color grading capabilities and in a 100% consistent manner.
International Diamond Laboratories cutting-edge technology measures the spectrum of the diamond (the amount of light absorbed by the diamond as function of color of the light itself). A mathematical method called the trisimulus method, assigns a coordinate in the 1931 CIE (Comission International d'Eclarage; International Illumination Comittee) diagram, which is associated to the measured spectrum. This can be converted in a saturation value and dominant wavelength.
Saturation determines the color intensity (the saturation value increases from D to Z color) while the color of the diamond is determined by the dominant wavelength (dominant wavelength determines if the diamond is orange, yellow, blue etc.).This characterizes the color of a diamond in a unique way. And a theoretical and experimentally verified framework, which describes color, supports this method.
The International Diamond Laboratories SatbarTM is a new, unique scale to grade the exact color of a diamond, fully respecting the existing D to Z color grades but more accurate and scientifically based.
The saturation value of the color of each diamond is determined and the region between two colors is divided in three parts. The saturation value of the color of a diamond is then placed in the appropriate region. That is the exact color grade of the diamond.