Diamonds are graded by four qualities known as the 4Cs: color, clarity, cut and carat weight. According to the Gemological Institute of America (GIA), “prior to 1940, however, there were no standard terms or factors that defined diamond quality.” Merchants “used many different and inconsistent terms.”
Robert M. Shipley, a former retail jeweler, founded GIA in 1931. He “standardized the diamond value terms to color, clarity, cut and carat weight and called them the 4Cs.” With GIA’s grading standards, the institute writes, diamond quality “can be communicated in a universal language so diamond purchasers know exactly what they are buying.”