When you combine these two reagents, one chalky and one viscous, a billow of expanding foam quickly forms in the area and then soon afterward hardens.
Alchemical ItemFormula Cost: 70 gp
Key Skill: Arcana or ThieveryTime: 30 min.
Utility Power Consumable (Standard Action)
Effect: You mix the plaster. Once before the end of the encounter, you can use a minor action to create an impression in the wet plaster of a footprint, a key, or a similar small object. Giving the hardened plaster to someone else allows that person to identify the footprint, duplicate the key, and so on as if he or she had the original item.
If the plaster is not used by the end of the encounter, it hardens into a lump.
Published in Mordenkainen's Magnificent Emporium, page(s) 131.