Hello BBking!
I am not into maces but can tell you that I have seen similar pieces on Hermann Historica auctions going as "Historism from the 19th century". I cannot rate this sadly.
As for the "Patina": I would leave it as it is to be honest. If it indeed is in any kind rust-preventing, then you would end up with a blank steel mace without any pitting which would look very artificial. My opinion.
If you still would want to go for revealing the plain steel, you could age it artificially afterwards with acid or (brace yourself) mustard to give it a older look after cleaning the black stuff, whatever it is.
A nice piece for hanging over the fireplace at home nethertheless
