Corrosion, platings, metals, colors


#1

when corrosion occurs, can the color tell you what the original plating was? my reading of the information on the internet was unclear on this point.

example: got some brake calipers, totally corroded. red/orange color. if water droplets are fresh on the piece, the color can be a bit brighter. the color is like the side of railroad tracks. When most people see this color corrosion, the overwhelming thought is that it is “rust”, which specifically is iron oxide.

when brass-brushed down, the pieces have a shiny silver appearance.

sounds like cadmium plating, which corrodes to red cadmium oxide - but also, because if it were in fact zinc plating, the corrosion would be a white powder (?). If the plating was expired, the steel below would presumably make a red/orange color corrosion.

I know zinc plating can be yellow or silver colored - come to think of it, some yellow-zinc bolts I have also have red/orange corrosion.

so do these observations say anything about what metals are on the piece?


#2

Cadmium plating is extremely thin and corrosion shouldn’t result in anything you could wire brush off, I think.