Perhaps only quality and damanage: I.e. a sword rusts a bit, it only would be damanaged a bit. This can be easilly be undone by cleaning. But if the sword rust to much the general quality of the sword lowers and that can only be repaired by a blacksmith.
So:
Quality: You need a blacksmith to improve it.
Damanage: Yo can repair it yourself, but if there is to much dmg the quality lowers.
I know you can improve like this the quality of the sword even higher then it was before, but that is not impossible in rl, so I wouldn\'t forbid that.