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Photographic processing or photographic development is the chemical means by which
photographic film Photographic film is a strip or sheet of transparent film base coated on one side with a gelatin emulsion containing microscopically small light-sensitive silver halide crystals. The sizes and other characteristics of the crystals determine the ...
or
paper Paper is a thin sheet material produced by mechanically and/or chemically processing cellulose fibres derived from wood, rags, grasses or other vegetable sources in water, draining the water through fine mesh leaving the fibre evenly distribut ...
is treated after
photographic exposure A photograph of the sea after sunset with an exposure time of 15 seconds. The swell from the waves appears foggy. In photography, exposure is the amount of light per unit area (the image plane illuminance times the exposure time) reaching a f ...
to produce a negative or positive
image An SAR radar image acquired by the SIR-C/X-SAR radar on board the Space Shuttle Endeavour shows the Teide volcano. The city of Santa Cruz de Tenerife is visible as the purple and white area on the lower right edge of the island. Lava flows a ...

image
. Photographic processing transforms the
latent image {{citations needed, date=November 2015 A latent image is an invisible image produced by the exposure to light of a photosensitive material such as photographic film. When photographic film is developed, the area that was exposed darkens and forms a ...

latent image
into a visible image, makes this permanent and renders it insensitive to light.Karlheinz Keller et al. "Photography" in Ullmann's Encyclopedia of Industrial Chemistry, 2005, Wiley-VCH, Weinheim. All processes based upon the
gelatin-silver The gelatin silver process is the most commonly used chemical process in black-and-white photography, and is the fundamental chemical process for modern analog color photography. As such, films and printing papers available for analog photography ...
process are similar, regardless of the film or paper's manufacturer. Exceptional variations include
instant film Instant film is a type of photographic film that was introduced by Polaroid Corporation to produce a visible image within minutes or seconds of the photograph's exposure. The film contains the chemicals needed for developing and fixing the photogra ...
s such as those made by Polaroid and thermally developed films.
Kodachrome Kodachrome is the brand name for a color reversal film introduced by Eastman Kodak in 1935. It was one of the first successful color materials and was used for both cinematography and still photography. For many years Kodachrome was widely used f ...
required
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 incorpora ...
's proprietary
K-14 process K-14 was the most recent version of the developing process for Kodak's Kodachrome transparency film before its discontinuation (the last revision having been designated Process K-14M). It superseded previous versions of the Kodachrome process used ...
. Kodachrome film production ceased in 2009, and K-14 processing is no longer available as of December 30, 2010.
IlfochromeIlfochrome (also commonly known as Cibachrome) is a dye destruction positive-to-positive photographic process used for the reproduction of film transparencies on photographic paper. The prints are made on a dimensionally stable polyester base as oppo ...
materials use the
dye destructionDye destruction or dye bleach is a photographic printing process, in which dyes embedded in the paper are bleached (destroyed) in processing. Because the dyes are fully formed in the paper prior to processing, they may be formulated with few constrai ...
process. Deliberately using the wrong process for a film is known as
Cross processing Cross processing (sometimes abbreviated to Xpro) is the deliberate processing of photographic film in a chemical solution intended for a different type of film. The effect was discovered independently by many different photographers often by mista ...
.


Common processes

All photographic processing use a series of chemical baths. Processing, especially the development stages, requires very close control of temperature, agitation and time.


Black and white negative processing

File:Photographic processing.jpg, center, upright=3.0, Black and white negative processing is the chemical means by which photographic film and paper is treated after photographic exposure to produce a negative or positive image. Photographic processing transforms the latent image into a visible image, makes this permanent and renders it insensitive to light. # The film may be soaked in water to swell the gelatin layer, facilitating the action of the subsequent chemical treatments. # The photographic developer, developer converts the latent image to macroscopic particles of metallic silver. # A
stop bathStop bath is a chemical used for processing black-and-white photographic films, plates, and paper. It is used to neutralize the alkaline developer, thus halting development. Stop bath is commonly a 2% dilution of acetic acid in water, though a 2.5% ...
, typically a dilute solution of
acetic acid Acetic acid , systematically named ethanoic acid , is a colourless liquid organic compound with the chemical formula CH3COOH (also written as CH3CO2H, C2H4O2, or HC2H3O2). Vinegar is no less than 4% acetic acid by volume, making acetic acid ...

acetic acid
or
citric acid Citric acid is a weak organic acid that has the molecular formula C6H8O7. It occurs naturally in citrus fruits. In biochemistry, it is an intermediate in the citric acid cycle, which occurs in the metabolism of all aerobic organisms. More than ...
, halts the action of the developer. A rinse with clean
water Water is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a solvent). It is vita ...
may be substituted. # The fixer makes the image permanent and light-resistant by dissolving remaining
silver halide A silver halide (or silver salt) is one of the chemical compounds that can form between the element silver and one of the halogens. In particular, bromine, chlorine, iodine and fluorine may each combine with silver to produce silver bromide (AgBr) ...
. A common fixer is ''hypo'', specifically
ammonium thiosulfate Ammonium thiosulfate (ammonium thiosulphate in British English) is an inorganic compound with the formula (NH4)2S2O3. It is white crystalline solid with ammonia odor, readily soluble in water, slightly soluble in acetone and insoluble in ethanol an ...
. # Washing in clean water removes any remaining fixer. Residual fixer can corrode the silver image, leading to discolouration, staining and fading. The washing time can be reduced and the fixer more completely removed if a hypo clearing agent is used after the fixer. # Film may be rinsed in a dilute solution of a
non-ionic An ion () is a particle, atom or molecule with a net electrical charge. The charge of the electron is considered negative by convention. The negative charge of an ion is equal and opposite to charged proton(s) considered positive by convent ...
wetting agent Surfactants are compounds that lower the surface tension (or interfacial tension) between two liquids, between a gas and a liquid, or between a liquid and a solid. Surfactants may act as detergents, wetting agents, emulsifiers, foaming agents, ...
to assist uniform drying, which eliminates drying marks caused by
hard water Hard water is water that has high mineral content (in contrast with "soft water"). Hard water is formed when water percolates through deposits of limestone, chalk or gypsum which are largely made up of calcium and magnesium carbonates, bicarbonat ...
. (In very hard water areas, a pre-rinse in distilled water may be required – otherwise the final rinse wetting agent can cause residual ionic calcium on the film to drop out of solution, causing spotting on the negative.) # Film is then dried in a dust-free environment, cut and placed into protective sleeves. Once the film is processed, it is then referred to as a ''negative''. The negative may now be
printed Printing is a process for mass reproducing text and images using a master form or template. The earliest non-paper products involving printing include cylinder seals and objects such as the Cyrus Cylinder and the Cylinders of Nabonidus. The ear ...
; the negative is placed in an enlarger and projected onto a sheet of photographic paper. Many different techniques can be used during the enlargement process. Two examples of enlargement techniques are
dodging and burning Dodging and burning are terms used in photography for a technique used during the printing process to manipulate the exposure of a selected area(s) on a photographic print, deviating from the rest of the image's exposure. In a darkroom print from a ...
. Alternatively (or as well), the negative may be scanned for digital printing or web viewing after adjustment, retouching, and/or manipulation.


Black and white reversal processing

This process has three additional stages: # Following the First Developer and rinse, the film is bleached to remove the developed negative image. This negative image is composed of metallic silver formed in the First Developer step. The bleach used here only affects the negative, metallic silver grains, it does not affect the unexposed and therefore undeveloped silver halide. The film then contains a latent positive image formed from unexposed and undeveloped silver halide salts. # The film is fogged, either chemically or by exposure to light. # The remaining silver halide salts are developed in the second developer, converting them into a positive image composed of metallic silver. # Finally, the film is fixed, washed, dried and cut.


Colour processing

Chromogenic The term chromogen is applied in chemistry to a colourless (or weakly 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. ...
materials use
dye couplers Dye coupler is present in chromogenic film and paper used in photography, primarily color photography. When color developer reduces ionized (exposed) silver-halide crystals, the developer is oxidized, and the oxidized molecules react with dye coupl ...
to form colour images. Modern colour negative film is developed with the
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 photofinis ...
and colour negative print materials with the
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 minilab wet silver halide digital printers of the types most common today in photo labs and drug stores, and for prin ...
. These processes are very similar, with differences in the first chemical developer. The C-41 and RA-4 processes consist of the following steps: # The colour developer develops the silver negative image by reducing the silver halide crystals that have been exposed to light to metallic silver, this consists of the developer donating electrons to the silver halide, turning it into metallic silver; the donation oxidizes the developer which then activates the dye couplers to form the colour dyes in each emulsion layer, but only does so in the dye couplers that are around unexposed silver halide.https://www.kodak.com/uploadedfiles/motion/US_plugins_acrobat_en_motion_education_kodak_color_films.pdf # A rehalogenising bleach converts the developed metallic silver into silver halide. # A fixer removes all silver halide, leaving only the dyes. # The film is washed, stabilised, dried and cut. In the RA-4 process, the bleach and fix are combined. This is optional, and reduces the number of processing steps. Transparency films, except
Kodachrome Kodachrome is the brand name for a color reversal film introduced by Eastman Kodak in 1935. It was one of the first successful color materials and was used for both cinematography and still photography. For many years Kodachrome was widely used f ...
, are developed using the E-6 process, which has the following stages: # A black and white developer develops the silver in each image layer. # Development is stopped with a rinse or a stop bath. # The film is fogged in the reversal step. # The fogged silver halides are developed and oxidation state, oxidized developing agents couple with the
dye couplers Dye coupler is present in chromogenic film and paper used in photography, primarily color photography. When color developer reduces ionized (exposed) silver-halide crystals, the developer is oxidized, and the oxidized molecules react with dye coupl ...
in each layer. # The film is bleached, fixed, stabilised and dried as described above. The Kodachrome process is called K-14 process, K-14. It is very involved, requiring 4 separate developers, one for black and white and 3 for color, reexposing the film in between development stages, 8 or more tanks of processing chemicals, each with precise concentration, temperature and agitation, resulting in very complex processing equipment with precise chemical control. In some old processes, the film emulsion was hardened during the process, typically before the bleach. Such a hardening bath often used aldehydes, such as formaldehyde and glutaraldehyde. In modern processing, these hardening steps are unnecessary because the film emulsion is sufficiently hardened to withstand the processing chemicals.


Further processing

Black and white emulsions both negative and positive, may be further processed. The image silver may be reacted with elements such as selenium or sulfur, sulphur to increase image permanence and for aesthetics, aesthetic reasons. This process is known as Photographic print toning, toning. In selenium toning, the image silver is changed to silver selenide; in sepia tone, sepia toning, the image is converted to silver sulphide. These chemicals are more resistant to atmospheric oxidizing agent, oxidising agents than silver. If colour negative film is processed in conventional black and white developer, and fixed and then bleached with a bath containing hydrochloric acid and potassium dichromate solution, the resultant film, once exposed to light, can be redeveloped in colour developer to produce an unusual pastel colour effect.


Processing apparatus

Before processing, the film must be removed from the camera and from its cassette, spool or holder in a light-proof room or container.


Small scale processing

Image:Light trap tank.jpg, 200px, A cut-away illustration of a typical light-trap tank used in small scale developing. In amateur processing, the film is removed from the camera and wound onto a developing tank, reel in complete darkness (usually inside a darkroom with the safelight turned off or a lightproof bag with arm holes). The reel holds the film in a spiral shape, with space between each successive loop so the chemicals may flow freely across the film's surfaces. The reel is placed in a specially designed light-proof tank (called daylight processing tank or a light-trap tank) where it is retained until final washing is complete. Sheet films can be processed in trays, in hangers (which are used in deep tanks), or rotary processing drums. Each sheet can be developed individually for special requirements. Stand development, long development in dilute developer without agitation, is occasionally used.


Commercial processing

In commercial processing, the film is removed automatically or by an operator handling the film in a light proof bag from which it is fed into the processing machine. The processing machinery is generally run on a continuous basis with films spliced together in a continuous line. All the processing steps are carried out within a single processing machine with automatically controlled time, temperature and solution replenishment rate. The film or prints emerge washed and dry and ready to be cut by hand. Some modern machines also cut films and prints automatically, sometimes resulting in negatives cut across the middle of the frame where the space between frames is very thin or the frame edge is indistinct, as in an image taken in low light. Alternatively stores may use minilabs to develop films and make prints on the spot without needing to send film to a remote facility for processing and printing. Some processing chemistries used in minilabs require a minimum amount of processing per given amount of time to remain stable and usable. Once rendered unstable due to low use, the chemistry needs to be completely replaced, or replenishers can be added to restore the chemistry to a usable state. Some chemistries have been designed with this in mind given the declining demand for film processing in minilabs, often requiring specific handling. Often chemistries become damaged by oxidation. Also, development chemicals need to be thoroughly agitated constantly to ensure consistent results. The effectiveness (activity) of the chemistry is determined through pre-exposed film control strips.


Environmental and safety issues

Many photographic solutions have high chemical oxygen demand, chemical and biochemical oxygen demand, biological oxygen demand (COD and BOD). These chemical wastes are often treated with ozone, peroxide or aeration to reduce the COD in commercial laboratories. Exhausted fixer and to some extent rinse water contain silver thiosulfate complex ions. They are far less toxic than free silver ion, and they become silver sulfide sludge in the sewer pipes or treatment plant. However, the maximum silver concentration in discharge is very often tightly regulated. Silver is also a somewhat precious resource. Therefore, in most large scale processing establishments, exhausted fixer is collected for silver recovery and disposal. Many photographic chemicals use non-biodegradable compounds, such as EDTA, DTPA, Nitrilotriacetic acid, NTA and borate. EDTA, DTPA, and NTA are very often used as chelation, chelating agents in all processing solutions, particularly in developers and washing aid solutions. EDTA and other polyamine polycarboxylic acids are used as iron ligands in colour bleach solutions. These are relatively nontoxic, and in particular EDTA is approved as a food additive. However, due to poor biodegradability, these chelating agents are found in alarmingly high concentrations in some water sources from which municipal tap water is taken. Water containing these chelating agents can leach metal from water treatment equipment as well as pipes. This is becoming an issue in Europe and some parts of the world. Another non-biodegradable compound in common use is surfactant. A common wetting agent for even drying of processed film uses Union Carbide/Dow Triton X-100 or octylphenol ethoxylate. This surfactant is also found to have estrogenic effect and possibly other harms to organisms including mammals. Development of more biodegradable alternatives to the EDTA and other bleaching agent constituents were sought by major manufacturers, until the industry became less profitable when the digital era began. In most amateur darkrooms, a popular bleach is potassium ferricyanide. This compound decomposes in the waste water stream to liberate cyanide gas. Other popular bleach solutions use potassium dichromate (a hexavalent chromium) or permanganate. Both ferricyanide and dichromate are tightly regulated for sewer disposal from commercial premises in some areas. Borates, such as borax (sodium tetraborate), boric acid and sodium metaborate, are toxic to plants, even at a concentration of 100 ppm. Many film developers and fixers contain 1 to 20 g/L of these compounds at working strength. Most non-hardening fixers from major manufacturers are now borate-free, but many film developers still use borate as the buffering agent. Also, some, but not all, alkaline fixer formulae and products contain a large amount of borate. New products should phase out borates, because for most photographic purposes, except in acid hardening fixers, borates can be substituted with a suitable biodegradable compound. Developing agents are commonly hydroxylation, hydroxylated benzene compounds or aminated benzene compounds, and they are harmful to humans and experimental animals. Some are mutagens. They also have a large chemical oxygen demand (COD). Ascorbic acid and its isomers, and other similar sugar derived reductone reducing agents are a viable substitute for many developing agents. Developers using these compounds were actively patented in the US, Europe and Japan, until the 1990s but the number of such patents is very low since the late-1990s, when the digital era began. Development chemicals may be recycled by up to 70% using an absorber resin, only requiring periodic chemical analysis on pH, density and bromide levels. Other developers need ion-exchange columns and chemical analysis, allowing for up to 80% of the developer to be reused. Some bleaches are claimed to be fully bio-degradable while others can be regenerated by adding bleach concentrate to overflow (waste). Used fixers can have 60 to 90% of their silver content removed through electrolysis, in a closed loop where the fixer is continually recycled (regenerated). Stabilizers may or may not contain formaldehyde.https://www.fujifilm.eu/fileadmin/countries/europe/United_Kingdom/Photofinishing_data_files/Technical_bulletins/TB_C41_E13_09-10.pdf


See also

* List of photographic processes * Fogging (photography) * Darkroom *
Cross processing Cross processing (sometimes abbreviated to Xpro) is the deliberate processing of photographic film in a chemical solution intended for a different type of film. The effect was discovered independently by many different photographers often by mista ...
* Caffenol


Notes


References

* *


External links


Kodak Processing manuals

The Massive Dev Chart - film development times

The Comprehensive Development Times Chart - Manufacturer's film development times database

Ilford guide to processing black & white film
{{DEFAULTSORT:Photographic Processing Science of photography Photographic processes,