Common Use Dates: 1963-2012
Alternate Names: Dye Destruction, Cibachrome, Ilfochrome
Mistaken For: Chromogenic
Process Family(s): Photographic, Silver, Subtractive Color, Dye, Gelatin Binder, Print
Silver dye bleach is a subtractive color photographic process. It is also a direct positive process in which prints were made directly from positive color transparency film; most photographic printing processes are printed from negatives. Silver dye bleach is based on the ability of metallic silver to act as a catalyst for the destruction, or bleaching, of dyes. At the height of its popularity, processing was simple taking about twelve minutes and requiring only three solutions: developer, bleach, and fixer. However the chemistry of the process was very complex.
Azo dyes were used, which are significantly more stable than dyes used in chromogenic color photographs. The print and transparency materials basically consist of three superimposed light sensitive silver gelatin emulsions, each spectrally sensitive to either red, green or blue light; this is called a monopack or integral tripack. They are also chromolytic meaning the dyes are incorporated into the emulsions during manufacturing—the red sensitive layer contains cyan azo dye, the green sensitive layer contains magenta azo dye, and the blue sensitive layer contains yellow azo dye. The support is a either triacetate, polyester, or resin coated paper support. This description is simplified; most silver dye bleach materials contain six or nine layers in total.
The exposure was made through positive color transparency film resulting in a negative silver image in each emulsion layer after development. The print was then placed in a bleach bath which was composed of a variety of ingredients including a strong acid, a silver ligand, and a bleach catalyst. The ligand lowered the reduction potential of the silver and the catalyst bounced back and forth between the silver particles and surrounding dye molecules in a complex oxidation reduction reaction, bleaching the dye surrounding the silver particle. In this reaction, the silver acted as a reducing agent in the presence of the bleach catalyst. The catalyst traveled to the dye molecule and reduced the azo dye adjacent to the silver forming a colorless water-soluble compound. The catalyst traveled back to the silver and the cycle continued until all the dye surrounding the silver was bleached forming a colorless halo around the silver particle. The halo is the image forming element. As the dye was bleached, the silver was also bleached; it was converted to silver iodide. The dye and silver bleaches were separate solutions initially, but were combined into a single bath in the 1970s. The amount of dye removed was directly related to the amount of silver present in the negative image resulting in a positive color image. Finally, the fixing solution removed the colorless dye compounds and silver iodide formed during the bleaching.
The most commercially successful silver dye bleach product was Cibachrome. Ciba and Ilford entered into a legal agreement to share information and jointly produce and market products beginning in 1963. In 1967 Ciba took over Ilford. Initially Cibachrome was released as a print service to print amateur photographs in Switzerland in 1963, but only for a very brief time. It was reintroduced in 1967 for professional use and in 1969 as a transparency material. These early products had a cellulose triacetate base. In 1980, Cibachrome-A for the amateur photographer was introduced with great success. Cibachrome II for professional use was introduced that same year with a self-masking system producing better quality reproduction of color. Materials introduced in 1980 were produced on an opaque or transparent polyester base or a resin coated paper support. The height of Cibachrome popularity was in the 1970s and early 1980s. In 1989, Ciba sold Ilford to the International Paper Corporation of America. The name of the product was changed from Cibachrome to Ilfochrome in 1991 as part of the agreement of the sale. In the late 1990s the speed of the material was increased so it could be exposed from a digital file with a laser exposure unit. Resin coated paper was discontinued in 2005 and all Ilfochrome production was discontinued in 2012.