Duplitized film stock was a type of film available through various companies used in color photography

Color photography

Color photography is photography that uses media capable of representing colors, which are traditionally produced chemically during the photographic processing phase...

 and special effects. It was introduced in the early 1910s. The stock was of standard gauge and thickness, but carried an emulsion on each side of the base.

For color film processes such as Cinecolor

Cinecolor

Cinecolor was an early subtractive color-model two color film process, based upon the Prizma system of the 1910s and 1920s and the Multicolor system of the late 1920s and 1930s. It was developed by William T. Crispinel and Alan M...

 or Prizma

Prizma

The Prizma Color system was a technique of color motion picture photography, invented in 1913 by William Van Doren Kelley and Charles Raleigh. Initially, it was a two-color additive color system, similar to its predecessor, Kinemacolor...

, red and blue or red and green negatives would be exposed, one to each emulsion. Yellow dye in the emulsion would slow the exposure light from the negative down from exposing both sides. When processed to black and white, the dye was washed out, and the respective images were converted from black and white to color by means of toning

Film tinting

Film tinting is the process of adding color to black-and-white film, usually by means of soaking the film in dye and staining the film emulsion...

both emulsions their appropriate color.