Abstract: In this paper we deal with paint-on-glass animation, which is a technique for making animated films by pushing slow-drying paints from frame to frame directly under the camera. As artwork is continuously destroyed upon creating new frames, the animator is not able to rehearse or refine the animation afterwards. Furthermore, due to impracticable issues like how to stack up layers containing wet paint or how to overlay masks on the wet medium, one has to take both creative as technical decisions for each shot. Our approach consists of an interactive paint setup that physically simulates paint media. Together with a set of digital tools the artist is relieved from the difficult task of sustaining a constant frame-to-frame coherence while animating and is given the possibility to modify or undo earlier paint modifications. Regarding the interaction part, the artist stays in full control by employing a tangible interface. This allows artists to push pigment with their fingers, use special-purpose digital brushes, or even to employ real life tools like paper tissue. Feedback from artists confirms the real-life behaviour of stretching and smudging the paint as well as interacting with the setup, resulting in a natural and reality-based methodology.