This potion is actually a light oil which is applied externally
to the dress and exposed flesh.

It then confers etherealness. In the
ethereal state the individual can pass through solid obiects - sideways,
upwards, downwards - or to different plones. Naturally, the individual
cannot touch non-ethereal objects.
The oil takes effect 3 rounds after application and it lasts for 4 + 1-4 turns unless removed with a weak acidic solution prior to the expiration of its normal effective duration.
It can be applied to obiects as well as creature one potion is sufficient to anoint a normal human and such gear as he or.she typically carries (2 or 3
weapons, garments, armor, shield, and the usual miscellaneous gear carried).
Ethereal individuals are invisible.
(Cf. phase door spell, and TRAVEL IN THE KNOWN PLANES OF EXISTENCE hereafter.)