Powder of Sympathy (3.5e Equipment)
From D&D Wiki
The Powder of Sympathy: This alchemical substance is made by crushing Roman Vitriol (copper(II)sulphate), filtering it through a sieve, covering it, and allowing it to air-dry in the hot sun. It is plentiful and cheap to produce, even for amateur alchemists.
To make good use of the powder, apply it to a weapon that has harmed someone. The wound made by the weapon will begin to heal, at the rate of 1 hitpoint per day, as long as the weapon remains covered by the powder.
This powder also gives a +1 alchemical bonus to Heal checks when the weapon that made the wound is in the healer's possession.
One vial costs 2 gp and weighs 1/2 lb.
Wikipedia: Powder of Sympathy