An axe ... what type ?

[kronckew]

black oil based paint was commonly used for corrosion protection both civilian and military, lots of armory & field grade weapons, armour, helmets etc. were blackened for storage between wars or protection in the field. i'd not remove it. i might even redo it (black rustoleum?). there are also acrylic based tannic acid products (find under auto products) that turn nasty red rust into a stable black form while priming the metal for a top coat. if t were a valuable antique weapon i might just oil it occasionally (and put a stained ash or hickory haft on it.

p.s. - i'm a dummy. just noticed this is actually, as lee said, a side axe, the blade offset to one side and the chisel grind is is used in woodworking to flatten and square timbers for beams - typically used by standing on or along the trunk and swinging the edge along the side, thus a bit heavy helps. it may have gone to war with an engineer for constructing siege engines & fortifications, but they were mostly civil carpentry tools. also called a broad axe.

see https://www.youtube.com/watch?v=EpB4zvoTV1c

and

https://www.youtube.com/watch?v=O2R_ZyPqwfo