Directors Norman McLaren and Evelyn Lambert hung some of the film to dry in windows of their work space in Montreal. Because of the pollution, dirt ended up drying onto the film as well. Lambert suggested projecting the film to see what it looked like. They ended up using this "dirty film" in parts of the finished work.
The technique used to create the images in the film is called camera-less animation. Images are painted directly on blank film stock or, in some instances, etched from the black emulsion of exposed film stock.