<P> However, all of these were glass - based plate products . Panchromatic emulsions on a film base were not commercially available until the 1910s and did not come into general use until much later . Many photographers who did their own darkroom work preferred to go without the seeming luxury of sensitivity to red--a rare color in nature and uncommon even in man - made objects--rather than be forced to abandon the traditional red darkroom safelight and process their exposed film in complete darkness . Kodak's popular Verichrome black - and - white snapshot film, introduced in 1931, remained a red - insensitive orthochromatic product until 1956, when it was replaced by Verichrome Pan . Amateur darkroom enthusiasts then had to handle the undeveloped film by the sense of touch alone . </P> <P> Experiments with color photography began almost as early as photography itself, but the three - color principle underlying all practical processes was not set forth until 1855, not demonstrated until 1861, and not generally accepted as "real" color photography until it had become an undeniable commercial reality in the early 20th century . Although color photographs of good quality were being made by the 1890s, they required special equipment, long exposures, complex printing or display procedures and highly specialized skills, so they were then exceedingly rare . </P> <P> The first practical and commercially successful color "film" was the Lumière Autochrome, a glass plate product introduced in 1907 . It was expensive and not sensitive enough for hand - held "snapshot" use . Film - based versions were introduced in the early 1930s and the sensitivity was later improved . These were "mosaic screen" additive color products, which used a simple layer of black - and - white emulsion in combination with a layer of microscopically small color filter elements . The resulting transparencies or "slides" were very dark because the color filter mosaic layer absorbed most of the light passing through . The last films of this type were discontinued in the 1950s, but Polachrome "instant" slide film, introduced in 1983, temporarily revived the technology . </P> <P> "Color film" in the modern sense of a subtractive color product with a multi-layered emulsion was born with the introduction of Kodachrome for home movies in 1935 and as lengths of 35 mm film for still cameras in 1936 . During the next several decades, color remained much more expensive than black - and - white and required much more light, factors which combined to delay its widespread adoption . Decreasing cost and increasing sensitivity gradually overcame these impediments . By the 1970s color film predominated in the consumer market, while the use of black - and - white film was increasingly confined to photojournalism and fine art photography . </P>

Film is sensitive to which of the following