Dust of Appearance
This plain pouch holds a single handful of sparkling dust, which it periodically renews.
Wondrous Item 17,000 gp
Power Encounter (Standard Action)
Pull a handful of dust from the pouch and throw it into the air (close blast 3). Doing this creates a zone that lasts until the end of the encounter. Invisible creatures and objects within or entering the blast become visible and can't become invisible again until the end of the encounter.
Published in Player's Handbook, page(s) 253.