A rusty sword is a broken sword that can be repaired by bringing it to Tindel Marchant in Port Khazard and paying 100 coins or repaired on a whetstone or on an armour stand in a Player-owned houseworkshop.[1] All three options have a chance to break the sword, however the chance of it breaking on the whetstone or armour stand decreases with Smithing level.[2] Successfully repairing a rusty sword yields 25 Smithingexperience.
^Jagex. Mod Ash's Twitter account. 14 February 2017. Archived from the original on 19 December 2021. Mod Ash: "Your Smithing level controls the chance of breaking it, but has no bearing on what sword it becomes if you succeed."