Infusion Stone of Poison

Toxic Pebble. You can put this tiny stone into a vial of water to infuse it with poison. If it remains in the vial for one week, the stone is fully dissolved and the water turns into a vial of Alchemist’s Poison. You can use the poison in this vial to coat one slashing or piercing weapon or up to three pieces of ammunition. Applying the poison takes an action. Once applied, the poison retains potency for 1 minute before drying. A creature hit by the poisoned weapon or ammunition must make a Constitution saving throw (DC 12). On a failed save they take 2d4 Poison damage. On a successful save they take half damage.   If the vial remains closed for longer durations after the stone has been put in it, the strength of the poison increases. After one month,the DC becomes 14, and the damage 4d4. After one year, the DC becomes 16, and the damage 8d4, and after ten years, the DC becomes 18, and the damage 16d4.