I've got this beautifully toned Buffalo nickel, but I can't figure out the grade. I'm thinking it's MS64, but I'll leave it to the experts here. And why would a nickel tone like this? I was not aware that nickel was so reactive...
Actually from a chemical standpoint, nickel is quite reactive, much more so than copper, which is only moderately more reactive than silver...however when it comes to toning...my chemistry fails to account for it.
My chemistry's pretty, um, informal, but I imagine it has to do with passivation -- forming a layer that's sturdy and impermeable, which slows further chemical attack. If not for passivation, we wouldn't be able to use aluminum for much of anything -- water would corrode it away to hydrogen and dust. Same thing with magnesium.
