They're blades, aren't they? Black blades are not formed by fighting other users of the same weapon. It happens when their user leaves them permanently black with their Haki. It's unknown if this is some advanced form of Armament Haki or if it happens when someone uses a blade for a long time.

I had a feeling the answer would be something like that. But I wish we would see more users with black blades that aren't just swords you feel me? It's always been swords that have become a black blade. Nowhere in history as far as I know has someone achieved a black blade that isn't a sword/katana of some sort.

Probably.

Yeah I guess

Maybe gaban did it!?!? (I remember he uses axes right)

WB used a Naginata and it’s a Supreme Grade so it’s likely that any bladed weapon can become a black blade

Yeah but I doubt Gaban has permanent black blades. Maybe he does and it's to early. I'd hope so because not only does it confirm other bladed weapons can become a black blade, but also that his armament haki is top notch.