Barber Nickel cleaning?

[HawgBonz]

While rummaging for points around one of the cutovers at the club I found what I believe to be a Barber Liberty Series Nickel.
It was right beside a fallen over chimney on an old homeplace.
Anybody know what to do that may clean it up. I scrubbed it with water and a toothbrush.
But that's about it.

 

[Flashpoint]

I wonder would electrolysis work on that? If that's rust it must have some iron in it.

 

[beamernc]

Looks like it was burned.

 

[HandyDave]

Maybe try some vinegar. Vinegar will clean all sorts of stuff.