Stone of Sharpening

Any sword or edged weapon struck against this temporarily enchanted rock has its edge perfectly sharpened and oiled, giving it a +3 damage bonus against the next target struck, +2 against the second, and +1 against the third. After the third blow has been struck, there are no other special effects. The stone can sharpen metal, obsidian, and bone weapons, as many as the caster has levels. To prepare the spell, the caster wraps a cloth around the stone, which can be no more than 2 feet in diameter, and soaks it with oil. The cloth is set on fire and allowed to burn until it disintegrates. The stone can then be used to sharpen as many weapons as the caster has levels of experience.