Pre 1900 Nickel Corrosion Staining

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?

 

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Both have copper in them.

 

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.

 

If it's copper oxide, it could possibly be removed, but I imagine it would leave a mark on the coin. If it's an area depleted of nickel, nope, nothing to be done.

I have a 1912-S nickel with very heavy orange staining. @BadThad, the creator of VerdiCare, indicated that that product might make a little headway against the staining, but he seemed to think it was a long shot. I haven't tried it yet.

(Edit: tagging BadThad on the off chance that he'd like to comment about the coin in the OP. He's a metallurgist, and probably forgets daily more than I've ever learned on the topic.)

 

It very well might be, but I'd like to see angle Pics first. I was thinking it was "staining" of some sorts.

 

I was thinking it possibly could be a Improperly mixed alloy AKA Woodie. Both sides usually streak in the same direction.
This is an MS60

 

I agree, appears to be stained from God knows what. It's had a long,hard life. It's always good to rule out surface residues:

The first steps to conservation are always to follow the polarity ladder: water>acetone>xylene (24 hr each)

 

Love the toning on the Buffalo. I've had coins that had the same characteristics.

Bruce