Snix's Float Salve
This is an unguent that, 40-60 seconds after it's removed from its potion bottle, is much, much lighter than air.
When spread on an object, it forms a strong bond with the object -- one that makes it nearly impossible to remove while the unguent remains potent. (Note: sages will generally be careful to apply this unguent without touching it for this reason.) The unguent from a single potion vial is capable of compensating for as much as 600 pounds of heavier-than air mass.
The material that makes this potion will gradually lose its potency after being applied, weakening in potency over the course of two to three hours.