The Master Stone is a special diamond used to define another diamond’s color during its grading process. The definition of the diamond’s color is a delicate and complex task. Simple gauges are incapable of providing the required level of accuracy – this is why Master Stones are customarily used for examination and comparison purposes.
This comparison between the color of the examined diamond and that of the Master Stone is conducted against a white paper background (or any other white background that is non-florescent), and under ordinary artificial light.
There are several criteria for a diamond to serve as a Master Stone: It must be round and have a clarity level of SI and above, weigh at least 70 points, and possess pre-defined proportions according to a special table. In addition, Master Stones must be colored according to color grading defined by the Gemological Institute of America (GIA).
