A C-Print (chromogenic print), also known as a silver halide print, or a dye coupler print, is a photographic print made from a color negative, transparency, or digital image, and developed using a chromogenic process. They are composed of three layers of gelatin, each containing an emulsion of silver halide, which is used as a light-sensitive material, and a different dye coupler of subtractive color which together, when developed, form a full-color image. Developing color by using oxidized developers was first suggested by German chemist Benno Homolka who, in 1907, successfully developed insoluble indigo-blue and red dyes on a latent image by oxidizing indoxyl and thio-indoxyl respectively. He additionally noted these developers could create beautiful photographic effects. The potential of oxidized developers in a color photographic process however, was first realized by another German chemist, Rudolf Fischer, who, in 1912, filed a patent describing a chromogenic process to develop both positives and negatives using indoxyl, and thio-indoxyl-based color developers as dye couplers in a light-sensitive silver halide emulsion. The following year he filed a patent listing various color developers and dye couplers, which have historically been used in Agfachrome and are still in use today in Fujichrome Velvia and Provia, and Ektachrome. In spite of this, Fischer never created a successful color print due to his inability to prevent the dye couplers from moving between the emulsion layers.
This first solution to this problem, found by Agfa workers Gustav Wilmanns and Wilhelm Schneider, who created a print made of three layers of gelatin containing subtractive color dye couplers made of long hydrocarbon chains, and carboxylic or sulfonic acid. This turned the dye couplers into micelles which can easily be scattered in the gelatin while loosely tethering to it. Agfa patented both the developer for this print and its photographic process and promptly developed and released Agfacolor Neu, the chromogenic print, a color print film that could be developed using a transparency, in 1936.
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