Alchemist's Rack

Alchemist's Rack or "stone rot" is typically stored in an airtight leather wineskin cured with rare preservative unguents, alchemist's rack is a powerful alchemical sealant with special deteriorative properties. When squeezed out of its container and exposed to air, bone paste quickly hardens, so in order to apply it to a surface or object one must typically squeeze the paste directly onto the material to be affected. One wineskin of Alchemist's Rack is a single use, one dose item. As an action, you may apply Alchemist's Rack onto an object or restrained, paralyzed, unconscious, or incapacitated creature and when your turn ends, it will harden into a brittle cast that is as hard as stone. If the creature starts a turn encased in Alchemist's Rack they may try to make a DC 18 Strength check to escape. It may repeat this check once per minute. Another creature may free a creature bound in Alchemist's Rack if they use a bludgeoning or piercing weapon to try to break the cast off of them (Strength check DC 15). For each minute that Alchemist's Rack is applied to an object or creature, it deals 1d6 acid damage. When applied to stone structures it deals this damage ignoring the damage threshold to the structure it is being applied to as it continues to spread throughout the stonework of the structure. The chemicals in alchemist's rack last for 2 days, at which point the chemicals become inert and it becomes indiscernible from regular stone.

Alchemist's rack is magical only for the purposes of ignoring magical resistances. It is otherwise a mundane item crafted through mundane methods. 
One wineskin full of alchemist's rack may be crafted with a DC 20 Intelligence check plus your proficiency bonus with Alchemist's Supplies. Crafting this difficult to make item takes 1500 gp worth of rare materials and 8 hours worth of work. If you fail the check, then all the supplies you tried to use to create the Alchemist's rack are wasted.

Notes: Damage: Acid