I always have had a fondness for war nickels, ever since I was a little kid collecting coins.
I think it was the easy to read mint-mark on the back.
Out here we get that same type of corrosion on them, or a weird almost tar-like encrustation.
Carl
Nice war nick.I'de try soaking in olive oil just to bust up that crud.It's worked for me in the past.
Personaly I don't clean up coins more then soaking overnight in soapy water then rinse under running water unless I can't make out a date or mm.
But to each their own. Good luck.........................................