This black, tarry substance can be used to paint a single black doorway on a flat surface. A pot contains enough paint to create one doorway. While painting, you must concentrate on a plane of existence other than the one you currently occupy. If you are not interrupted, the doorway can be painted in 5 minutes. Once completed, the painting opens a two-way portal to the plane you imagined. The doorway is mirrored on the other plane, often appearing on a rocky face or the wall of a building. The doorway lasts for 1 week or until 5 gallons of water with flecks of silver worth at least 2,000 gp is applied to one side of the door.