Parkerizing is a process Harley-Davidson started using in the 1920's to put an anti-corrosive finish on bolts and various other parts. Parkerizing was a more simple process than Cadmium Plating, as The Cad process required the use of cyanide. Parkerizing is a fairly simple hand process, using a Manganese or a Zinc phosphate solution to produce either a black or a gray finish. Parkerizing can only be done on Ferrous metals; will not work with metals such as Stainless, Brass, Copper or Aluminium. The Parkerized color is also affected by the hardness of the steel. Any good gun shop will sell Parkerizing materials. Parkerizing is also known as Phosphating and has been around since the 1800's.