Synthetic Diamonds

   The first proved manufacture of synthetic diamonds was announced on Feb. 15, 1955, by the General Electric Company. The diamonds were produced by compressing graphite under pressures of 800,000 to 1,800,000 pounds per square inch and temperatures above 5000 °F. The diamonds were tiny and not of gem quality. Synthetic diamonds weighing less than one thousandth of a carat are used as industrial abrasives.
   Research on diamond synthesis continued at Gen­eral Electric, and in 1970 that company announced the successful synthesis of gem-quality diamonds. The diamonds were clear and large, some weighing more than one carat.