The physical properties of a diamond are altered by: applying a cationic elemental plasma to a diamond at a plasma temperature of less than 300° C.; allowing the cationic plasma to chemically bond with atoms in defects within the diamond; and removing the plasma from the diamond. The cationic elemental plasma may exemplary be selected from the group consisting of as H+, Na+, Li+ and K+. It is preferred that no plasma is projected from a source at the diamond and that the plasma is provided as an environment surrounding the diamond.