Haze On A Jefferson Proof Nickel: Fixable?

I would try the sudsy ammonia again. It works well on 40% Ikes.

From the OP's picture, it looks like the "milk-spot" has already been scrubbed before. (Milk spots on a coin are there for good).

These are cupronickel coins. That is an early stage, complex copper-nickel type verdigris. It is very resistant to conservation in my experience. Often, hydrogensulfide can join the party to form very tough nickel and copper sulfides which become complexed with the copper verdigris. Generally, that stuff is like 100x harder than regular copper verdigris.

You're only hope is that the layers are very thin and not a lot of metal was removed. However, this is a proof, usually the smallest amount of metal loss ruins the surface finish. If you do manage to remove those spots, you'll still be able to see where they were....at least in my experience.

Did you try VERDI-CARE™? Maybe a little on a Q-tip? I don't like using VC on proofs but it is only a $5 coin.

Good Luck!

Well, Thad has basically confirmed my worries. I will give it a soak in some acetone, and tuck it away in a flip. Who knows, it a decade, that toning might be really cool? Or maybe we do the cigar box thing on this coin.

After a few hours in acetone, with axial pictures. I think axial covers up a lot of surface condition sins like bad toning and luster loss, but amplifies others like scratches.

Any thoughts on whether those spots are long term stable?

Looking good!