Using coloured pencil on frosted cels was a practical solution, since the drawing and colouring could be done in one step. Drawing only the essential elements accelerated the process and became Frédéric Back's signature technique. The relative transparency of the frosted cel made it possible to use multiple layers over an unchanging background, whereas with paper everything had to be redrawn. Overlaying cels not only created a multiplane effect but also produced a certain image density. To bring out the colour of the chalk-pastel backgrounds, Back would apply a coat of fixative. Since the quick-drying product he used was highly toxic, he would usually wait until he was alone in the studio. Unfortunately, this would ultimately cost him the use of his right eye, irreparably damaged while fixing a drawing for Crac!.
Drawing from the film Crac!.