Howdy! I've come across several shields and 3CN nickels over the years with this exact dull pinkish to pink-brown staining. Does anyone know exactly what it is?
There are so many things that can stain a coin it's hard to tell. It could have been subjected to any number of environmental contaminants over it'd many years of life. Bruce
Nickel is more reactive than copper, so if anything starts attacking the coin's surface, it can leave areas with more copper, which of course is pink or red. Copper can oxidize to copper(1) oxide, Cu2O, which is red or brown. There could be other stuff going on, but I think that's likely the most common cause.
So these could be areas devoid of nickel? It's definitely not a stain in the traditional sense. It's inorganic and not a residue. If that's true there's really nothing that can be done except polishing off the whole top layer. Definitely not going to do that. Mostly curious if it was some kind of copper or nickel +iron oxide that could be conserved.
