Rusted Blade

One weapon you touch corrupts under your grasp, growing dull and pitted with a rustline patina covering it. For the duration, any Living creature damaged by the weapon must succeed on a Constitution saving throw or contract Filth Fever. Despite the change in appearance, this spell has no ill effect on the target weapon.
 

Transmutation Level: Assassin 3, Druid 3, Sorcerer 4, Wizard 4, Wu Jen 4 (metal), Components: V, S, Casting Time: 1 standard action Range: Touch Target: One weapon touched Duration: 1 round/level (D) Saving Throw: Will negates (object, harmless) and Fortitude negates Spell Resistance: Yes (object, harmless)   Your touch corrupts the substance beneath your fingers. Where once it gleamed, it now grows dull and pitted. You cause a rustlike patina to temporarily cover the target weapon. (Despite its name, the spell can affect any kind of weapon regardless of material). For the duration of the spell, any living creature damaged by the weapon must succeed on a Fortitude save or contract filth fever (DMG 292). Use the spell's normal save DC for the initial saving throw, but use filth fever's normal DC 12 for later saves. Multiple applications of the disease do not stack, but even a creature that succeeds on one or more saves must continue to save each time it takes damage from the weapon. Despite the change in appearance, this spell has no ill effect on the target weapon.