 Eastman, Agfa, Gevaert, and DuPont all manufactured bipack film stocks for use in colour processes from the 1920s onwards.Two strips of film, one orthochromatic and having a very thin and superficial red dye layer on its emulsion, and one panchromatic, would be exposed together with their emulsions pressed into close contact, the orthochromatic one nearest the lens.The orthochromatic negative ended up reversed from the normal handedness, but as the two negatives were often contact-printed onto one duplitized film for subsequent colour-toning, as in the Prizma process, this often worked to the advantage of the laboratory.