"Cross processing (sometimes abbreviated to Xpro) is the procedure of deliberately processing photographic film in a chemical solution intended for a different type of film. The effect was discovered independently by many different photographers often by mistake in the days of C-22 and E-4. Traditionally, cross processing color slide film in negativ-film process chemicals is most common.

Color cross processed photographs are often characterized by unnatural colors and high contrast. The results of cross processing differ from case to case, as the results are determined by many factors such as the make and type of the film used, the amount of light exposed onto the film and the chemical used to develop the film. It produces different colour-effects, that cannot be fully controlled." Wikipedia