Yellow and brown diamonds are somtimes bombarded with radiation, or irradiated, to produce colored diamonds. Usually the radiation treatment is followed by heating to 1000° to improve the color. Irradiated diamonds usually retain their new color, however they can change color if heated by a jeweler's torch.

Because fancy color diamonds (any color other "white") are rare and expensive, irradiated diamonds cost a fraction of the price of a natural colored diamond.

Radiation treatment can sometimes be detected under magnification. appearing as concentrations, or zones of color.