Ooh I love these damage ID threads! I'll guess either a poor attempt at trying to copper plate it or it came in contact with a chemical and it reacted/got stained.
The composition of the Liberty nickel was 75% copper and 25% nickel. It could be circulation wear, but more than likely, it is PMD. Chris
It got in contact with some chemicals that would cause that? I have electroplated and I admit, it looks quite like that, maybe electroplating then.
These metals were alloyed; they were homogenously mixed. These coins were not clad or in layers. The coin shown has been stained or plated in some manner.