Dye transfer is a continuous-tone color photographic printing process. It was used to print Technicolor films, as well as to produce paper colour prints used in advertising, or large transparencies for display.
History
The use of dye imbibition for making full-color prints from a set of black-and-white photographs taken through different color filters was first proposed and patented by Charles Cros in 1880. It was commercialized by Edward Sanger-Shepherd, who in 1900 was marketing kits for making color prints on paper and slides for projection. Imbibition printing was initially in monochrome. The basic underlying principle is that bichromate development of a silver gelatine photographic emulsion results in the gelatine being differentially tanned or hardened in proportion to the exposure received, and blackening obtained. When washed in hot water a relief gelatine image is obtained which is then immersed in a dye bath, washed off in a 3% acetic acid solution then to the 1% acetic acid holding bath. Photographic paper was removed from the conditioner and matrix was rolled into contact with photographic paper consisting of a paper base, a baryta coating to improve light reflectance and a gelatine coating without the light sensitive silver salts in regular photographic bromide paper. The gelatine absorbs dye from the matrix. Finally, the print is dried between blotters, or by heat. The colour process depends on superimposing three images in the subtractive colours: cyan, magenta and yellow in exact register, facilitated by means of register pins mounted at the edge of a glass rolling bed, using a purpose designed punch to make holes at the edge of the matrix films. As three matrices are required for each print, which are the same size as the print, the process is relatively expensive. Colour separation negatives together with their high contrast highlight masks that keep specular highlights clear from fogging over by exposing the contrast reducing masks through them. Technicolor introduced dye transfer in its Process 3, introduced in the feature filmThe Viking, which was produced by the Technicolor Corporation and released by Metro-Goldwyn-Mayer. Technicolor's two previous systems were an additive color process and a physically problematic subtractive color process, the latter requiring two prints cemented together back-to-back. Process 3 used an imbibition process pioneered by the Handschiegl color process, which had been created in 1916 for Cecil B. DeMille's feature film Joan the Woman. Technicolor further refined the imbibition dye transfer process in its Process 4, introduced in 1932, which employed three simultaneously filmed negatives. In the 1940s, this process was popularized by the work of Jeannette Klute at Eastman Kodak for general-purpose graphic arts work, but not for motion picture work, which remained exclusive to Technicolor, and is sometimes referred to by such generic names as "wash-off relief printing" and "dye imbibition" printing. The graphic arts process requires making three printing matrices from three colour separation negatives made from a colour transparency original or at one time directly in a large format camera fitted with a sliding plate holder or film holder. The matrices, which are relief gelatine images on a film support absorb dye in proportion to the optical densities of the gelatin relief image. Successive placement of the dyed film matrices, one at a time, "transfers" each primary dye by physical contact from the matrix to a mordanted, gelatin-coated paper. It took a technician one whole day to produce one print. Firstly, three colour separation negatives were made using three high contrast highlight masks to produce three contrast reducing and colour correction unsharp masks. The unsharp masks were made with an oblique light source hole fitted onto the register pin, and then the right hole pressed down onto the pin. Then a rubber roller is taken and the matrix firmly rolled away from the operator into contact with the paper which is kept in a pile in a conditioning bath. The dye is absorbed by the paper for one minute after which the matrix is picked up by the farthermost corners and peeled off the paper. The same procedure is followed for the magenta and yellow matrices.
Status today
In 1994, Eastman Kodak stopped making all materials for this process. The dyes used in the process are very spectrally pure compared to normal coupler-induced photographic dyes, with the exception of the Kodak cyan. The dyes have excellent light and dark fastness. The dye transfer process possesses a larger color gamut and tonal scale than any other process, including inkjet. Another important characteristic of dye transfer is that it allows the practitioner the highest degree of photographic control compared to any other photochemicalcolor print process. A peculiar advantage of the process was that skilled Dye Transfer retouchers would use the same dyes the image was printed with to fill in blank white spaces between two or three separate colour photographs such as a background shot one or more human figures, and more often than not a product shot to produce a "strip in". Using the same dyes for photographically printing the images and for retouching meant that colour matching by eye would not show up differently when rephotographed.
