A covering for an exterior rear view mirror assembly for motor vehicles includes a plurality of covering parts defining a contact point between each of the plurality of covering parts. The anode body is formed, by pressing together finely divided powder, flakes or fibers of a sacrificial anode material such as zinc to define a porous body having pores therein. Control and uniformity are insured by use of conductive rapid thermal annealing in hot wall reactors, with massive heated plates closely spaced from the substrate surfaces. The state control circuit is coupled to the power source unit, and includes a pulse width modulator, a sensing coil, and a control transistor coupled electrically in series.