In 1855 Alphonse Louis Poitevin patented a carbon process to make prints from photographic negatives and positives by using an emulsion containing particles of carbon or colored, non-silver pigment to form the image. The original purpose of this process was not to make colored images but to provide a permanent solution to the fading and discoloration problems that plagued the early positive silver print processes. The carbro process, considered the most versatile of the carbon processes, evolved from Thomas Manly’s Ozotype (1899) and Ozobrome processes (1905). The name carbro was given to an improved version of the process in 1919 by the Autotype Company to signify that carbon tissue was used in conjunction with a bromide print (car/bro). [1|2|20|1476]Additional examples:
 
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Separation negatives were exposed through red, green, and blue filters and used to make a matched set of bromide prints. In the carbro process, the image is formed by chemical action when the pigmented carbon tissue is placed face-to-face with a fully processed black-and-white print on bromide paper. When the print and the tissue are held in contact, the gelatin of the tissue becomes insoluble in water in proportion to the density of the silver on the bromide print. After soaking, this sandwich is separated. The tissue is transferred onto a paper support, where it is washed until only a pigment image remains. This is repeated for each of the three-pigmented tissues, and the final print is an assemblage of cyan, magenta, and yellow (CMY) carbon tissues in register, producing a full-color print. Autotype’s tricolor carbro process produced splendid color prints from the CMY pigmented tissues. Using a bromide print created numerous advantages, including the following: (1) enlargements could be made from small-format negatives; (2) ordinary exposure light sources could be used instead of high-intensity ultraviolet; (3) contrast was determined by the bromide print; and (4) regular photographic printing controls such as burning and dodging could be used. The perfecting of the carbro process demonstrated it was possible to make full-color images from black-and-white materials and was an important step on the path towards a practical chromogenic method for making color images (see the following section, Subtractive Film and Chromogenic Development). Other variations of this three-color subtractive assembly printing method, such as the affordable Vivex process (1931 – 1939), followed. [1|2|20|1477]

The first color images to receive widespread viewing were not made by direct photographic means. They were created indirectly by applying the subtractive principles of color photography on William Kurtz’s photoengraver’s letterpress in New York in 1892. Using an early halftone process, a scene of fruit on a table was photographed, screened, and run through the press three times (a separate pass for each of the three subtractive colored inks: cyan, magenta, and yellow). The halftone process is a printing method that enables a photographic image to be reproduced in ink by making a halftone screen of the original picture. The screen divides the picture into tiny dots that deposit ink in proportion to the density of the original image tones in the areas they represent. Kurtz’s color reproductions were bound into the January 1, 1893, issue of Photographische Mittheilungen, published in Germany. Even though it still was not possible to obtain color prints from color film in an ordinary camera, this printing procedure pointed to a way in which color images could be photographically produced. [1|2|21|1478]

In the imbibition process, a dye image is transferred from a gelatin relief image to a receiving layer made either of paper or film. Charles Cros described this method of “hydrotypie” transfer printing in 1880 and suggested it could be used to transfer three individual dye images in register. The Hydrotype (1881) and the Pinatype (1905) were examples of the early use of this process. One of the notable, though not widely used, relief matrix processes was developed by Dr Arthur Traube and introduced in 1929 as the Uvatype, which was an improved version of his earlier Diachrome (1906) and dye mordant Uvachrome (1916) processes. The Eastman Wash-off Relief process (1935) was a refinement of the imbibition process that was replaced by the improved Dye Transfer process (1946 – 1993). The widest commercial application of the imbibition process was the Technicolor process, originally introduced as a two-color system in 1916, for producing motion-picture release prints. [1|2|22|1479]

Between 1911 and 1914 Rudolf Fischer of Germany, working closely with Karl Schinzel of Austria, invented a color film that had the color-forming ingredients, known as color couplers, incorporated directly into it. This discovery, that color couplers could produce images by chromogenic development (see next paragraph), laid the foundation for most color film processes in use today. In this type of film, known as an integral tri-pack, three layers of emulsion are stacked one on top of another, with each layer sensitive to red, green, or blue. [1|2|23|1480]

Through the process known as chromogenic development, the color couplers in each layer of the emulsion form a dye image in complementary colors of the original subject. During chromogenic development, the dye image is made at the same time as the silver halide image is developed in the emulsion. The silver image is then bleached away, leaving only the dye, which is fixed to form the final image. The problem with the original RGB color tri-pack was that unwanted migration of the dyes between the three layers could not be prevented, causing color inaccuracies in the completed image. [1|2|23|1481]

Some black-and-white films, such as Ilford’s XP2 Super 400 or Kodak’s BW400CN, also make use of the chromogenic system to deliver various densities of black dye. Any lab that develops conventional color negative film (C-41 process) can process these products. For best results, these negatives can be printed on RA-4 paper or scanned and digitally printed. [1|2|23|1482]

In 1930, Kodak Research Laboratories hired Leopold Godowsky, Jr., and Leopold Mannes, musicians who had been experimenting with making color films in makeshift labs since they were teenagers. By 1935 they were able to overcome the numerous technical difficulties and produce the first truly successful integral tri-pack subtractive color reversal film. This film was called Kodachrome and first marketed as a 16mm movie film¹. It was said, only half jokingly, that it took God and Man (Godowsky and Mannes) to solve the problem of the color couplers’ unwanted migration between the emulsion layers. Their ingenious solution to this problem was to use the color couplers in separate developers during the processing of the film, rather than build them into the film emulsion itself. [1|2|23|1483]

In Kodachrome film, only one exposure was needed to record a latent image of all three primary colors. The top emulsion layer was sensitive only to blue. Under this was a temporary yellow-dye filter that absorbed blue light, preventing it from affecting the emulsion below. This temporary yellow filter, which dissolved during processing, allowed the green and red light to pass through and be recorded in the proper emulsions below. [1|2|23|1484]

Kodachrome was first developed into a negative and then, through reversal processing, into a positive. During the second development, the colors of the original subject were transformed into the complementary dyes of cyan, magenta, and yellow, which formed the final color image. Then the positive silver images were bleached away and the emulsion was fixed and washed. This left a positive color image that was made up of only subtractive colored dyes, with no silver. [1|2|24|1485]

In 1936 Kodachrome was made for the 35mm still photography market. Eastman Kodak was concerned that nobody would want a tiny slide that had to be held up to the light to be seen. In a shrewd move, by 1938 the company was returning each processed slide in a 2 × 2-inch cardboard “Readymount” so that it could be projected onto a screen. At this time Kodak also introduced the Kodaslide projector, reinvigorating the Victorian-era magic lantern slide exhibition, which had been in decline. By the late 1930s the union of the 35mm camera with Kodachrome launched the modern color boom and signaled the end of the additive screen processes such as Autochrome. [1|2|24|1486]

Kodachrome was the first film to achieve the dream of an accurate, inexpensive, practical, and reliable method for making color images. The major drawbacks of Kodachrome were its slow speed (the original ISO of 8 was eventually increased to 200), its complex processing that meant the film had to be sent to a special lab, and the difficulty and expense of making prints from transparencies. Kodachrome’s legendary characteristics, which were commemorated in the naming of Utah’s Kodachrome Basin State Park as well as the 1973 popular song by Paul Simon, allowed it to reign as the benchmark in color accuracy, rendition, contrast, and grain until it finally succumbed to improved and much faster chromogenic films and digital image capture. After a 74-year run as a photography icon, Kodachrome was “retired” in 2009. [1|2|24|1487]

In 1936 Agfa released Agfacolor Neu film, which overcame the problem of migrating the color couplers by making their moleculesvery big. In this manner, they would mix easily with the liquid emulsion during the manufacturing of the film. Once the gelatin that bound them together had set, the color coupler molecules were trapped in the tiny spaces of the gelatin and unable to move. This was the first three-layer, subtractive color reversal film that had the color couplers built into the emulsion layers themselves and employed a single developer to make the positive image. This simplified process allowed the photographer to process the film. Kodak countered Agfacolor with its own version of the process, Ektachrome, in 1946. [1|2|25|1488]

Agfa brought out a color negative film in 1939 from which positive color prints could be made directly on a special companion paper. Kodak followed suit in 1942 with Kodacolor, which is considered to be the first subtractive color negative film that completely solved the problem of the color couplers migrating from layer to layer in the emulsion. Color negative films, such as Kodacolor, overcame the limitation of each image being one-of-a-kind since any number of positive prints could be made from a color negative film. [1|2|26|1489]

The processing method created for Kodacolor is, with many improvements, the basis for all color negative film processes utilized today. In this process, currently called C-41, a single developer produces a negative silver image and a corresponding dye image in all three layers of the emulsion at the same time. Bleach is used to remove all the silver, leaving only the dye. The film is fixed, washed, and dried, which completes the process. [1|2|27|1490]

When making prints from a chromogenic negative with the subtractive method, the light is filtered in the enlarger before it reaches the negative. Correct color balance can thus be achieved in a single exposure. One of the three dye layers in the negative is usually left unfiltered. Printing is simplified because it is not necessary to use more than two filters at one time to make a print. The subtractive method also enables pictures to be made directly from transparency film in a reversal printing process, such as Ilfochrome Classic P3. [1|2|27|1491]

The silver dye-bleach (or dye-destruction) process is a method of making color prints from positives or negatives. Bleach is used to remove the unnecessary dyes from the emulsion, rather than using chromogenic development to produce dyes in the emulsion. In 1933 Hungarian chemist Bela Gaspar commercially introduced this method as Gasparcolor for use in color motion picture work. Today’s Ilfochrome Classic materials, introduced as Cibachrome in 1963, make use of this process to make prints directly from transparencies. [1|2|28|1492]

Modern “instant” photography, or, more accurately, selfprocessing film, began in 1948 with the marketing of Edwin Land’s first black-and-white Polaroid process. Polacolor, which Polaroid introduced in 1963 and was the first full-color, peel-apart print film, developed itself and produced a color print in 60 seconds. In 1976 Kodak launched its own line of instant products but 10 years later was forced to withdraw them when Polaroid won patent infringement suits against Kodak’s design. In 2008 Polaroid ceased its film production. However, in 2010 the owners of the Polaroid brand announced a newly designed version of the Polaroid OneStep camera that uses Polaroid Color 600 Instant Film, which is still being manufactured by the Impossible Project. Fuji continues to manufacture its own line of instant (Instax) films as well as an instant film camera. [1|2|29|1493]

Self-processing materials, such as Polaroid, use the internal dye diffusion-transfer process, often called the diffusion transfer process. It operates by causing the dye-formers to transfer out of the negative emulsions layer(s) to a single receiving layer (also in the material), where the visual positive image forms. The three phases of the process — negative development, transfer, and positive development — happen simultaneously, so that the positive images begin to form almost immediately. [1|2|29|1494]

The Polaroid SX-70 camera and film (1972 – 1981), and the later Spectra camera and film (1986 – present) called Time Zero, make use of the diffusion-transfer method. After the shutter is pressed, the motor drive, which is powered by a battery in each film pack, automatically ejects the film through a set of rollers that break a pod of reagent located at the bottom of each piece of film. Development is then automatic and requires no timing. Development can take place in daylight because the light-sensitive negative is protected by opaque dyes in the reagent. Both the positive and negative images are contained within each sheet of film. The diffusion transfer process was also the basis for Polaroid’s Polachrome, an additive color screen film. [1|2|30|1495]