A PROTECTIVE OXIDE FILM MAY BE LOCATED ON THE SURFACE OF A COBALT NICKEL MAGNETIC ALLOY BY TREATING THE SURFACE OF SUCH AN ALLOY WITH AN AQUEOUS SOLUTION OF AN INORGANIC OXIDIZING AGENT AND AN ORGANIC CHELATING AGENT CAPABLE OF BUFFERING THE SOLUTION SO AS TO OXIDIZE THE SURFACE. SUCH TREATMENT IS PREFERABLY CARRIED ON FOR SUFFICIENTLY LONG PERIODS TO FORM AN ADHERENT, SUBSTANTIALLY CONTINUOUS OXIDE LAYER FORM METAL IN THE ALLOY. THE CONCENTRATION OF THE INGREDIENTS IN THE TREATMENT SOLUTION CAN BE VARIED DEPENDING UPON THE SPECIFIC INGREDIENTS USED, THE REATTIVITY OF THE PARTICULAR ALLOY BEING TREATED, THE TEMPERATURE OF THE TREATMENT SOLUTION AND THE THICKNESS OF THE OXIDE FILM DESIRED. AFTER SUCH TREATMENT THE ALLOY SURFACE IS PREFERABLY WASHED SO AS TO REMOVE ENTRAINED INGREDIENTS AND THEN IS PREFERABLY HEATED AT A TEMPERATURE OF FROM 230 TO 280*C. FOR A PERIOD OF FROM ONE-HALF TO FOUR HOURS IN EITHER AN INERT ATMOSPHERE, AN OXYGEN ATMOSPHERE OR AN ATMOSPHERE CONTAINING OXYGEN AND ONE OR MORE INERT OR SUBSTANTIALLY INERT GASES.