The Dip is a greenish, ghastly chemical seen in Who Framed Roger Rabbit. Loved by no toon (except Doom), and feared by all toons (and Doom at the end). It is Judge Doom's preferred method of Toon execution. According to Lieutenant Santino, it's a mixture of turpentine, acetone, and benzine, all of which are paint-thinners. While relatively harmless to humans, any toon that comes in contact with it will melt instantly, and is apparently the only surefire way to kill a toon (although Eddie Valiant gets most of The Toon Patrol members to laugh themselves to death). Ironic enough, Judge Doom ends up being dipped himself near the end of the film, after revealing himself to be actually a toon.
The dip is used in the historical toon incident as a way for Judge Doom to eradicate Toon-kind from existence. It was long since destroyed but its evidence is still avaliable in the foresnics lab.