Basically, my technique was to paint on a piece of glass fixed to a light box. I would paint on the glass with oil so that it wouldn’t dry, and I could play with it for hours.
The single light source came from beneath the glass, revealing the textures and details of brushes movements.
I worked a lot with transparency. The more paint, the darker the image, and therefore the animation becomes about gesture, and the texture of brushstrokes; it’s a very physical, organic process.