method for coating a rectifier metal with alkali metal molybdenate / alkali metal silicate or alkali metal tungstenate / alkali metal silicate comprises immersing a rectifier metal and a cathodic metal in an electrolytic solution and imposing voltage potential between the two electrodes . the voltage is first raised to about 240 to about 260 volts during an oxidation stage , and thereafter to about 380 - 420 volts to form the desired coating . unique electrolytic solutions are provided for the electrodeposition method .