Damn, looking at the comments here I realize sometimes I DO have more knowledge on some topics than other people. If you guys don't know that's a bronze sword, bronze is a metal that's well known due to its corruption-resistant properties. When bronze develops that green patina you see on the sword it also creates a sort of protective layer that shields the rest of the metal from oxygen and prevents it from rusting away.
Quick note meant to say corrosion not corruption lmao.