Diamond treatment

A method for reducing the color of type 1B diamonds containing dispersed nitrogen, which dispersed nitrogen imparts to said diamonds a color ranging from yellow to green, the method includes the step of heat treating said diamonds at a temperature in the range of 1,600.degree. C. to 2,200.degree. C. under a pressure at which said diamonds are crystallographically stable at the particular temperature employed, said heat treatment being continued so as to effect aggregation of the dispersed nitrogen and thereby reduce the color of said diamonds, the improvement comprising in combination with said heating step the additional step of:

• reducing the time required for said heat treatment step to achieve said color reduction by employing an exposing step prior to said heat treatment step, said exposing step comprising exposing the diamond to irradiation of sufficient strength to cause atomic displacements in said diamond and continuing said irradiation until atomic displacement occurs, the flux of said irradiation being such as to produce at least 10.sup.+18 vacancies per cubic centimeter in said diamond.