Here is a close up pic of the black zinc and wash (rainbow hue) after resto. When i looked close at the original plating on the wiper it appeared to be a low quality black zinc and did not appear to have a phosphate finish. there was a lot of inconsistencies between original pieces in terms of finish quality. good luck

i might be starting a small operation redoing this stuff myself but i am still in the R&D stage. Stay tuned.... Dont want to rush into something without being able to give a high quality of work.