that the negative image would look positive, and was popular in America until around 1870. 1855: Gum printing Orange colored dichromate has photosensitivity when it is mixed with colloids such as gum arabic, albumen, or gelatin. Using that feature, Alphonse Poitevin invented the gum printing process. It gained in popularity after 1898, and again in 1960s and 1970s because of its unique look. 1858: Tintype (also called Ferrotype and Melainotype) In this photographic process the emulsion was painted directly onto a japanned (varnish finish) iron plate. it was much cheaper and sturdier than the Ambrotype and Daguerreotype. 1861: RGB additive color modelApplied physician James Clerk Maxwell made the first color photo by mixing red, green, and blue light. 1871: Gelatin dry plateRichard L. Maddox discovered that gelatin could be a carrier for silver salts. By 1879, the gelatin dry plate had replaced the collodion wet plate. It was a revolutionary innovation in photography since it needed less light exposure, was usable when dry, meaning photographers no longer needed to pack and carry dangerous liquids, and could be standardized because it could be factory produced. 1873: Platinum printing (Platinotype)William Willis patented platinum printing in Britain. The process rapidly spread and became a dominant method in Europe and America by 1894 since it had a visibly different color tone compared to albumen and gelatin silver prints. Late 1880s: Gelatin silver printThis has been the major photograph printing process since the late 1880s up to the present. Prints consist of paper coated with an emulsion of silver halide in gelatin. The surface is generally smooth; under magnification, the print appears to sparkle. 1889: KallitypeDr. W. W. J. Nicol invented and refined the Kallitype. Vandyketype, or Single Kalliitype, is the simplest type of Kalltype and creates beautiful brown images. 1889: Film negativesCellulose nitrate film was developed by Eastman Kodak in 1889 and refined in 1903. It is made of silver gelatin on a cellulose nitrate base. The negatives are flammable and therefore can be dangerous. Nitrate sheet film was used widely though the 1930s, while nitrate roll film was used through the 1950s. The nitrate base was replaced with cellulose acetate in 1923. By 1937, Cellulose diacetate was used as the base, and beginning in 1947 Cellulose triacetate was used. Polyester film was introduced around 1960. 1935: Color photographsKodak introduced color film and transparencies in 1935. The first process was called Kodachrome. Ektachrome, introduced