negative films of the same era, having been produced in ISO 4 to ISO 20,000. Current instant film formats typically have an ISO between 100 and 1000. Two companies currently manufacture instant film: Fujifilm, with Instax integral film for its Instax cameras, and Polaroid (previously The Impossible Project) for older Polaroid cameras (600, SX-70, and 8×10) and its I-Type cameras. How it works Instant positive film (which produces a print) uses diffusion transfer to move the dyes from the negative to the positive via a reagent. The process varies according to the film type. Roll/pack film In 1947 Edwin H. Land introduced the Polaroid-Land process. The first instant films produced sepia tone photos. A negative sheet is exposed inside the camera, then lined up with a positive sheet and squeezed through a set of rollers which spread a reagent between the two layers, creating a developing film "sandwich". The negative develops quickly, after which some of the unexposed silver halide grains (and the latent image it contains) are solubilized by the reagent and transferred by diffusion from the negative to the positive. After a minute, depending on film type and ambient temperature, the negative is peeled away to reveal the picture which was transferred to the positive receiving sheet. True black and white films were released in 1950 after problems with chemistry stabilization were overcome. With that being said, photographers and enthusiasts still practice with this limited, special and discontinued film, with both older Polaroid stocks or Fujifilm FP-100C or FP-3000B varieties. Multiple companies made film backs that would adapt camera to use this film with a specific detachable back. Film Photography Project is a website and store dedicated to providing film and analogue photographic and motion picture medium to those who need it. In an article, they talked about the use of packfilm specifically adapting it to large format cameras. Subtractive color films Color film is much more complex due to multiple layers of emulsion and dye. The negative consists of three emulsion layers sensitive to the primary colors (red, green, and blue) each with a layer of developing dye beneath it of the complementary color (cyan, magenta, and yellow). Once light exposed the negative, the reagent is spread between the negative and positive and the developing dye layer migrates though diffusion to the positive surface where it forms the photo. Emulsion layers exposed to their respective color block