You designate a vertical plane made up of no more than one 10-foot square per your level. This is the "wall" itself. You also choose a side of the wall. Each 10-foot square of the wall emanates out to that side, filling five 10-foot cubes in a straight line. These cubes are the "warded area." The wall is invisible, except from creatures inside the warded area, who perceive it as a transparent shimmer in the air.
Creatures looking through the wall perceive creatures in the warded area as if they were under the effect of an invisibility spell. Creatures may pass through the wall or otherwise enter and exit the warded area at will and without destroying the spell. However, if any creature in the warded area attacks a viewer, the attacker is no longer affected by that wall of invisibilty, and is therefore visible through the wall.
Material component: Ten eyelashes encased together in gum arabic.