Something's Rotten in Faerun
Oil of Etherealness
This potion is actually a light oil that is applied externally to clothes and exposed flesh, conferring etherealness. In the ethereal state, the individual can pass through solid objects in any direction—sideways, upward, downward—or to different planes. The individual cannot touch non-ethereal objects.
The oil takes effect three rounds after application, and it lasts for 4 + 1d4 turns unless removed with a weak acidic solution prior to the expiration of its normal effective duration. It can be applied to objects as well as creatures. One potion is sufficient to anoint a normal human and such gear as he typically carries (two or three weapons, garments, armor, shield, and miscellaneous gear). Ethereal individuals are invisible.