Chromogenic photography is

photography Photography is the visual art, art, application, and practice of creating durable images by recording light, either electronically by means of an image sensor, or chemically by means of a light-sensitive material such as photographic film. It i ...

that works by a

chromogen In chemistry, the term chromogen refers to a colourless (or faintly coloured) chemical compound that can be converted by chemical reaction into a compound which can be described as "coloured". There is no universally agreed definition of the term. ...

forming a conventional silver image and then replacing it with a

dye A dye is a colored substance that chemically bonds to the substrate to which it is being applied. This distinguishes dyes from pigments which do not chemically bind to the material they color. Dye is generally applied in an aqueous solution and ...

image. Most films and papers used for color photography today are chromogenic, using three layers, each providing their own

subtractive color Subtractive color or subtractive color mixing predicts the spectral power distribution of light after it passes through successive layers of partially absorbing media. This idealized model is the essential principle of how dyes and inks are u ...

. Some chromogenic films provide black-and-white negatives, and are processed in standard color developers (such as the C-41 process). In this case, the dyes are a neutral color.

Description

Chromogenic film or

paper Paper is a thin sheet material produced by mechanically or chemically processing cellulose fibres derived from wood, Textile, rags, poaceae, grasses or other vegetable sources in water, draining the water through fine mesh leaving the fibre e ...

contains one or many layers of

silver halide A silver halide (or silver salt) is one of the chemical compounds that can form between the Chemical element, element silver (Ag) and one of the halogens. In particular, bromine (Br), chlorine (Cl), iodine (I) and fluorine (F) may each combine wi ...

(AgX) emulsion, along with

dye couplers Dye coupler is present in chromogenic film and paper used in photography, primarily color photography. When a color developer reduces ionized (exposed) silver halide crystals, the developer is oxidized, and the oxidized molecules react with d ...

that, in combination with processing chemistry, form visible

dyes A dye is a colored substance that chemically bonds to the substrate to which it is being applied. This distinguishes dyes from pigments which do not chemically bind to the material they color. Dye is generally applied in an aqueous solution and ...

. In processing, the silver image of each layer is first developed. In concert with the dye couplers in each layer, the process subsequently forms dyes only in those areas where silver is present. In full-color chromogenic materials, multiple layers of emulsion are sensitized to different wavelengths of

light Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 te ...

. Three layers are usually present, generally sensitive to red, green, and blue colored light. Cyan-colored dye is formed on the red-sensitive layer, magenta-colored dye is formed on the green-sensitive layer, and yellow-colored dye is formed on the blue-sensitive layer, following generally the CMY color model. Some chromogenic

black-and-white Black-and-white (B&W or B/W) images combine black and white in a continuous spectrum, producing a range of shades of grey. Media The history of various visual media began with black and white, and as technology improved, altered to color. ...

negative films also exist, mainly to exploit the wide availability of

C-41 process C-41 is a chromogenic color print film developing process introduced by Kodak in 1972, superseding the C-22 process. C-41, also known as CN-16 by Fuji, CNK-4 by Konica, and AP-70 by AGFA, is the most popular film process in use, with most photo ...

ing. These films have softer grain and less contrast than traditional

films. In these films, a single emulsion layer has

panchromatic Panchromatic emulsion is a type of black-and-white photographic emulsion that is sensitive to all wavelengths of visible light. Description A panchromatic emulsion renders a realistic reproduction of a scene as it appears to the human eye, altho ...

sensitivity. The dye image is typically slightly blue because of the choice of

. Examples of black-and-white chromogenic negative films are Ilford XP2 Super and Fujifilm Neopan 400CN, produced in partnership with Ilford. Kodak have ceased production of their

Kodak The Eastman Kodak Company (referred to simply as Kodak ) is an American public company that produces various products related to its historic basis in analogue photography. The company is headquartered in Rochester, New York, and is incorpor ...

BW400CN film. It is also possible to develop a standard black and white silver gelatine film or print using specially formulated chromogenic developers so that a colored dye image only remains after processing, the silver image being totally or partially bleached away during processing.The Master Photographer's Toning Book, Tim Rudman, Argentum, 2002, p146 et seq (Chromogenic Toners) Each microscopic point of chromogenic dye formation is called a dye cloud. After the formation of dyes is complete, the silver image is removed in processing by a specialty

photographic fixer Photographic fixer is a mix of chemicals used in the final step in the photographic processing of film or paper. The fixer stabilises the image, removing the unexposed silver halide remaining on the photographic film or photographic paper, leavi ...

called bleach fix or blix. A processing variation called skip bleach, most popular in motion picture negative processing, leaves the silver image partially or completely intact, yielding a type of contrast enhancement. The most common chromogenic processes are C-41 for color (and chromogenic

) negative film,

RA-4 RA-4 is Kodak's proprietary name for the chemical process most commonly used to make color photographic prints. It is used for both minilab wet silver halide digital printers of the types most common today in photo labs and drug stores, and for pr ...

for color negative paper (see

Type C print A chromogenic print, also known as a C-print or C-type print, 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 co ...

), and E-6 for

slide film In photography, reversal film or slide film is a type of photographic film that produces a positive image on a transparent base. Instead of negatives and prints, reversal film is processed to produce transparencies or diapositives (abbrevia ...

. A great deal of research effort has been placed by manufacturers, most notably

Fujifilm , trading as Fujifilm, or simply Fuji, is a Japanese multinational conglomerate headquartered in Tokyo, Japan, operating in the realms of photography, optics, office and medical electronics, biotechnology, and chemicals. The offerings from ...

Ilford Photo Harman Technology, trading as Ilford Photo, is a UK-based manufacturer of photographic materials known worldwide for its ILFORD branded black-and-white film, papers and chemicals. Historically it also published the ''Ilford Manual of Photograph ...

, and

, into controlling the color and tonal characteristics of their chromogenic film and paper. The sensitization of the

emulsions, the composition and mixture of the

, and the chemical interactions of layers upon one another during processing (called interlayer effects), are the subjects of numerous patents.

is apparently unique in its use of a fourth (cyan-sensitive) color layer in certain of its negative films. Like the traditional

process, the main hazardous waste product of chromogenic processing consists of silver compounds dissolved in the used fixer. This waste is usually processed to recover the valuable dissolved

silver Silver is a chemical element with the Symbol (chemistry), symbol Ag (from the Latin ', derived from the Proto-Indo-European wikt:Reconstruction:Proto-Indo-European/h₂erǵ-, ''h₂erǵ'': "shiny" or "white") and atomic number 47. A soft, whi ...

in metallic form, and to allow safe disposal of the remaining substance. A history of improper handling of waste fixer has led to environmental contamination. For example, the disposal of untreated waste fixer into the

sanitary sewer A sanitary sewer is an underground pipe or tunnel system for transporting sewage from houses and commercial buildings (but not stormwater) to a sewage treatment plant or disposal. Sanitary sewers are a type of gravity sewer and are part of ...

s and storm drains of

New York City New York, often called New York City or NYC, is the most populous city in the United States. With a 2020 population of 8,804,190 distributed over , New York City is also the most densely populated major city in the U ...

has led to high levels of dissolved silver in the

Hudson River The Hudson River is a river that flows from north to south primarily through eastern New York. It originates in the Adirondack Mountains of Upstate New York and flows southward through the Hudson Valley to the New York Harbor between Ne ...

References

* *{{cite web , url = http://notesonphotographs.eastmanhouse.org/index.php?title=Chromogenic_Print , title = Definition of Chromogenic Print on George Eastman House Notes on Photographs website , publisher = notesonphotographs.eastmanhouse.org , accessdate = 2009-10-31 , archive-url = https://web.archive.org/web/20101106224729/http://notesonphotographs.eastmanhouse.org/index.php?title=Chromogenic_Print , archive-date = 2010-11-06 , url-status = dead Photographic processes