Chromogenic
Encyclopedia
Chromogenic refers to color photographic processes in which a traditional silver image is first formed, and then later replaced with a colored dye
image.
or paper
contains one or many layers of silver halide
emulsion, along with dye couplers
which are capable of forming visible dyes in combination with processing chemistry. 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
. 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
negative films also exist, mainly to exploit the wide availability of C-41 process
ing. These films have softer grain and less contrast than traditional silver halide
films. In these films, a single emulsion layer has panchromatic
sensitivity. The dye image is typically slightly blue because of the choice of dye couplers
, and this tends to produce a dark sepia tone when printed on full-color chromogenic paper.
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
called bleach fix or blix. A processing variation called skip bleach, most popular in motion picture negative processing, allows the silver image to be left partially or completely intact, yielding a type of contrast enhancement.
The most common chromogenic processes are C-41
for color and black-and-white
negative film, RA-4
for color negative paper (see Type C print
), and E-6
for slide film.
A great deal of research effort has been placed by manufacturers, most notably Fujifilm
, Ilford Photo
, and Kodak, into controlling the color and tonal characteristics of their chromogenic film and paper. The sensitization of the silver halide
emulsions, the composition and mixture of the dye couplers
, and the chemical interactions of layers upon one another during processing (called interlayer effects), are the subjects of numerous patents. Fujifilm
is apparently unique in its use of a fourth (cyan-sensitive) color layer in certain of its negative films.
Like the traditional silver halide
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
in metallic form, and to allow safe disposal of the remaining substance. However 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
s and storm drain
s of New York City
has led to high levels of dissolved silver in the Hudson River
.
Dye
A dye is a colored substance that has an affinity to the substrate to which it is being applied. The dye is generally applied in an aqueous solution, and requires a mordant to improve the fastness of the dye on the fiber....
image.
Description
Chromogenic filmPhotographic film
Photographic film is a sheet of plastic coated with an emulsion containing light-sensitive silver halide salts with variable crystal sizes that determine the sensitivity, contrast and resolution of the film...
or paper
Photographic paper
Photographic paper is paper coated with light-sensitive chemicals, used for making photographic prints.Photographic paper is exposed to light in a controlled manner, either by placing a negative in contact with the paper directly to produce a contact print, by using an enlarger in order to create a...
contains one or many layers of silver halide
Silver halide
A silver halide is one of the compounds formed between silver and one of the halogens — silver bromide , chloride , iodide , and three forms of silver fluorides. As a group, they are often referred to as the silver halides, and are often given the pseudo-chemical notation AgX...
emulsion, along with dye couplers
Dye couplers
Dye coupler is present in chromogenic film and paper used in photography, primarily color photography. When color developer develops exposed silver-halide crystals, the developing agent molecules become oxidized, and the oxidized developer molecules react with dye coupler molecules to form dye in...
which are capable of forming visible dyes in combination with processing chemistry. 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
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...
. 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
CMY
CMY may refer to:*Sparta/Fort McCoy Airport in Sparta, Wisconsin*CMYK color model...
color model.
Some chromogenic black-and-white
Black-and-white
Black-and-white, often abbreviated B/W or B&W, is a term referring to a number of monochrome forms in visual arts.Black-and-white as a description is also something of a misnomer, for in addition to black and white, most of these media included varying shades of gray...
negative films also exist, mainly to exploit the wide availability of C-41 process
C-41 process
C-41 is a chromogenic color print film developing 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 photofinishing labs devoting at least one machine to this development process....
ing. These films have softer grain and less contrast than traditional silver halide
Silver halide
A silver halide is one of the compounds formed between silver and one of the halogens — silver bromide , chloride , iodide , and three forms of silver fluorides. As a group, they are often referred to as the silver halides, and are often given the pseudo-chemical notation AgX...
films. In these films, a single emulsion layer has panchromatic
Panchromatic
Panchromatic film is a type of black-and-white photographic film that is sensitive to all wavelengths of visible light. A panchromatic film therefore produces a realistic reproduction of a scene as it appears to the human eye. Almost all modern photographic film is panchromatic, but some types are...
sensitivity. The dye image is typically slightly blue because of the choice of dye couplers
Dye couplers
Dye coupler is present in chromogenic film and paper used in photography, primarily color photography. When color developer develops exposed silver-halide crystals, the developing agent molecules become oxidized, and the oxidized developer molecules react with dye coupler molecules to form dye in...
, and this tends to produce a dark sepia tone when printed on full-color chromogenic paper.
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
Photographic fixer is a chemical or 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, leaving behind the reduced metallic silver...
called bleach fix or blix. A processing variation called skip bleach, most popular in motion picture negative processing, allows the silver image to be left partially or completely intact, yielding a type of contrast enhancement.
The most common chromogenic processes are C-41
C-41 process
C-41 is a chromogenic color print film developing 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 photofinishing labs devoting at least one machine to this development process....
for color and black-and-white
Black-and-white
Black-and-white, often abbreviated B/W or B&W, is a term referring to a number of monochrome forms in visual arts.Black-and-white as a description is also something of a misnomer, for in addition to black and white, most of these media included varying shades of gray...
negative film, RA-4
RA-4 process
RA-4 is Kodak's proprietary name for the chemical process most commonly used to make color photographic prints. It is used for both digital printers of the types most common today in photo labs and drug stores, and for prints made with older-type optical enlargers and manual processing...
for color negative paper (see Type C print
Type C print
Chromogenic color prints are full-color photographic prints made using chromogenic materials and processes. These prints may be produced from an original which is a color negative, slide, or digital image. The chromogenic print process, was nearly synonymous with the 20th century color snapshot...
), and E-6
E-6 process
The E-6 process is a chromogenic photographic process for developing Ektachrome, Fujichrome and other color reversal photographic film....
for slide film.
A great deal of research effort has been placed by manufacturers, most notably Fujifilm
Fujifilm
is a multinational photography and imaging company headquartered in Tokyo, Japan.Fujifilm's principal activities are the development, production, sale and servicing of color photographic film, digital cameras, photofinishing equipment, color paper, photofinishing chemicals, medical imaging...
, Ilford Photo
Ilford Photo
Ilford Photo is a manufacturer of photographic materials known worldwide for its black-and-white film and papers and chemicals, as well as its range of Ilfochrome and Ilfocolor colour printing materials. Ilfochrome was formerly called Cibachrome, developed in partnership with the Swiss company...
, and Kodak, into controlling the color and tonal characteristics of their chromogenic film and paper. The sensitization of the silver halide
Silver halide
A silver halide is one of the compounds formed between silver and one of the halogens — silver bromide , chloride , iodide , and three forms of silver fluorides. As a group, they are often referred to as the silver halides, and are often given the pseudo-chemical notation AgX...
emulsions, the composition and mixture of the dye couplers
Dye couplers
Dye coupler is present in chromogenic film and paper used in photography, primarily color photography. When color developer develops exposed silver-halide crystals, the developing agent molecules become oxidized, and the oxidized developer molecules react with dye coupler molecules to form dye in...
, and the chemical interactions of layers upon one another during processing (called interlayer effects), are the subjects of numerous patents. Fujifilm
Fujifilm
is a multinational photography and imaging company headquartered in Tokyo, Japan.Fujifilm's principal activities are the development, production, sale and servicing of color photographic film, digital cameras, photofinishing equipment, color paper, photofinishing chemicals, medical imaging...
is apparently unique in its use of a fourth (cyan-sensitive) color layer in certain of its negative films.
Like the traditional silver halide
Silver halide
A silver halide is one of the compounds formed between silver and one of the halogens — silver bromide , chloride , iodide , and three forms of silver fluorides. As a group, they are often referred to as the silver halides, and are often given the pseudo-chemical notation AgX...
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
Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...
in metallic form, and to allow safe disposal of the remaining substance. However 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
Sanitary sewer
A sanitary sewer is a separate underground carriage system specifically for transporting sewage from houses and commercial buildings to treatment or disposal. Sanitary sewers serving industrial areas also carry industrial wastewater...
s and storm drain
Storm drain
A storm drain, storm sewer , stormwater drain or drainage well system or simply a drain or drain system is designed to drain excess rain and ground water from paved streets, parking lots, sidewalks, and roofs. Storm drains vary in design from small residential dry wells to large municipal systems...
s of New York City
New York City
New York is the most populous city in the United States and the center of the New York Metropolitan Area, one of the most populous metropolitan areas in the world. New York exerts a significant impact upon global commerce, finance, media, art, fashion, research, technology, education, and...
has led to high levels of dissolved silver in the Hudson River
Hudson River
The Hudson is a river that flows from north to south through eastern New York. The highest official source is at Lake Tear of the Clouds, on the slopes of Mount Marcy in the Adirondack Mountains. The river itself officially begins in Henderson Lake in Newcomb, New York...
.