It might surprise some to know that blue screens were used as far back as the 1930s in black-and-white films. In the 1933 film King Kong, the scene where Kong comes pounding through the gates was shot with blue behind the set. Because of the black-and-white film’s color sensitivity, it was possible to add filters so that the blue area did not receive any exposure. Thus, it was “simple” to reexpose the blue-screened parts of the film with the stop-motion of Kong. Other systems besides bluescreen systems were developed to create traveling mattes for films. Like many of the techniques to create color images on film, and the many film formats, most of these now lie in obscurity. Systems that used ultraviolet light or infrared-sensitive emulsions in two-strip motion picture cameras were experimented with and even used but eventually were abandoned due to technical hurdles in their implementation. A very successful technique, used with great success by the Walt Disney Studio in the 1950s and into the 1960s and 1970s, was the “sodium vapor” process (named for the lamp used to light the screen). This method generated mattes by simultaneously exposing, through prisms in modified Technicolor three-strip cameras, both the live-action footage and footage on a second strip of film that had an exposure only where it captured light from the yellow screen. The filmmakers were able to generate first-generation mattes for much of their work using this technique. Disney used this process to great result in films such as Mary Poppins (1964) and Bedknobs and Broomsticks (1971). In the 1980s, modification of older techniques mentioned above using ultraviolet lights to expose some or all portions of the subject (by now, miniatures painted with ultraviolet-sensitive paint) came into use. These techniques were used with success on films such as FireFox (1982). It was the groundbreaking work by Petro Vlahos in developing technology for creating color difference mattes that made all of these advances possible.