Transmutation
Level: Arcane 3
Components: V, S
Casting Time: Attack action
Range: Close (25 ft. + 5 ft./2 levels)
Target: One weapon or 50 projectiles, all of which must be in contact with each other at the time of casting
Duration: 10 minutes/level
Saving Throw: Will negates (harmless, object)
Spell Resistance: Yes (harmless, object)

This transmutation doubles the threat range of the weapon. A threat range of 20 becomes 19-20. A threat range of 19-20 becomes 17-20. A threat range of 18-20 becomes 15-20. The spell can be cast only on piercing or slashing weapons (and it does not stack with itself). If cast on arrows or crossbow bolts, the keen edge on a particular projectile ends after one use, whether or not the missile strikes its intended target.

This spell cannot be cast on a natural weapon, such as an unarmed strike.