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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 coated on one side with a containing microscopically small light-sensitive crystals. The sizes and other characteristics of the crystals determine the sensitivity, contrast, and of the ...
or
paper Paper is a thin sheet material Material is a substance Substance may refer to: * Substance (Jainism), a term in Jain ontology to denote the base or owner of attributes * Chemical substance, a material with a definite chemical composition * ...
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.">exposure_time.html" ;"title="sunset with an exposure time">sunset with an exposure time of 15 seconds. The swell from the waves a ...
to produce a negative or positive
image An image (from la, imago) is an artifact that depicts visual perception Visual perception is the ability to interpret the surrounding environment Environment most often refers to: __NOTOC__ * Natural environment, all living and non- ...

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 Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that can be visual perception ...

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 film. Instant film is a type of photographic film Photographic film is a strip or sheet of transparent film base coated on one side with a gelatin photographic emulsion, emulsion containing microscopically small light-sensitive silver halide c ...
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 , and is incorporated in . Kodak pro ...

Kodak
'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 Photographic paper is a coated paper, paper coated with a light-se ...
materials use the
dye destructionDye destruction or dye bleach is a photographic printing Photographic printing is the process of producing a final image on paper for viewing, using chemically sensitized paper. The paper is exposed to a photographic negative, a positive transpar ...
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 Photography is the art, application, and practice of creating durable image An SAR radar imaging, radar image acquired by the SIR-C/X-SAR rada ...
.


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

# The film may be soaked in water to swell the
gelatin Gelatin or gelatine (from la, gelatus meaning "stiff" or "frozen") is a translucent, colorless, flavorless food ingredient, commonly derived from collagen taken from animal body parts. It is brittle when dry and rubbery when moist. It may also ...
layer, facilitating the action of the subsequent chemical treatments. # The 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 film Photographic film is a strip or sheet of transparent film base coated on one side with a gelatin photographic emulsion, emulsion containing microscopically small light- ...
, 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 an organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form chains with other carbon s), millions of organic compounds are known. The study of the properties, reactions, ...

citric acid
, halts the action of the developer. A rinse with clean
water Water (chemical formula H2O) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known li ...

water
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 compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, e ...
. A common fixer is ''hypo'', specifically
ammonium thiosulfate Ammonium thiosulfate (ammonium thiosulphate in British English British English (BrE) is the standard dialect of the English language English is a West Germanic languages, West Germanic language first spoken in History of Anglo-Saxon ...

ammonium thiosulfate
. # 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 In the Outline of physical science, physical sciences, a particle (or corpuscule in older texts) is a small wikt:local, localized physical body, object to which can be ascribed several physical property, physical or ...
wetting agent Surfactants are compounds that lower the surface tension Surface tension is the tendency of liquid surfaces to shrink into the minimum surface area possible. Surface tension is what allows heavier than water i.e., denser than water object ...
to assist uniform drying, which eliminates drying marks caused by
hard water Hard water is water Water (chemical formula H2O) 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 orga ...
. (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 Printmaking, 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 Nabon ...
; 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 Photography is the art Art is a diverse range of (products of) human activities involving creative imagination to express technical proficiency, beauty, emotional power, or conceptual ...
. 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 Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, structure, properties, behavi ...
materials use
dye couplers Dye coupler is present in chromogenic film A film, also called a movie, motion picture or moving picture, is a work of visual art used to simulate experiences that communicate ideas, stories, perceptions, feelings, beauty, or atmosphere ...
to form colour images. Modern colour negative film is developed with the
C-41 process C-41 is a chromogenic The term chromogen is applied in chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, struct ...
and colour negative print materials with the RA-4 process. 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 halide is a binary phase, of which one part is a halogen atom and the other part is an chemical element, element or radical (chemistry), radical that is less electronegative (or more electropositive) than the halogen, to make a, e.g., fluoride, ...
. # 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 The E-6 process (often abbreviated to E-6) is a chromogenic Photographic processing, photographic process for developing Ektachrome, Fujichrome and other Reversal film, color reversal (also called slide or transparency) photographic film. Unlike so ...
, 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
oxidized (mild reducing agent) are added to powdered potassium permanganate (strong oxidizing agent), a violent redox reaction accompanied by self-ignition starts. Redox (reduction–oxidation, pronunciation: or ) is a type of chemical reaction A ...
developing agents couple with the
dye couplers Dye coupler is present in chromogenic film A film, also called a movie, motion picture or moving picture, is a work of visual art used to simulate experiences that communicate ideas, stories, perceptions, feelings, beauty, or atmosphere ...
in each layer. # The film is bleached, fixed, stabilised and dried as described above. The Kodachrome process is called 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 Formaldehyde ( , also ) (systematic nameA systematic name is a name given in a systematic way to one unique group, organism, object or chemical substance A chemical substance is a form of matter In classical physics and general chemist ...
and
glutaraldehyde Glutaraldehyde, sold under the brandname Cidex and Glutaral among others, is a disinfectant A disinfectant is a chemical A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance t ...
. 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 Selenium is a chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that ...

selenium
or
sulphur Sulfur (in nontechnical British English: sulphur) is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consis ...

sulphur
to increase image permanence and for
aesthetic Aesthetics, or esthetics (), is a branch of philosophy Philosophy (from , ) is the study of general and fundamental questions, such as those about Metaphysics, existence, reason, Epistemology, knowledge, Ethics, values, Philosophy of m ...

aesthetic
reasons. This process is known as toning. In selenium toning, the image silver is changed to
silver selenide Silver selenide (Ag2Se) is the reaction product formed when selenium toning analog silver gelatine photo papers in photographic print toning. The selenium toner contains sodium selenite (Na2SeO3) as one of its active ingredients, which is the sour ...
; in sepia toning, the image is converted to silver sulphide. These chemicals are more resistant to atmospheric 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 Hydrochloric acid +(aq) Cl−(aq) or H3O+ Cl− also known as muriatic acid, is an aqueous solution An aqueous solution is a solution Solution may refer to: * Solution (chemistry) Image:SaltInWaterSolutionLiquid.jpg, upMaking a salin ...

hydrochloric acid
and
potassium dichromate Potassium dichromate, , is a common inorganic compound, inorganic chemical reagent, most commonly used as an oxidizing agent in various laboratory and industrial applications. As with all hexavalent chromium compounds, it is acutely and chronically ...

potassium dichromate
solution, the resultant film, once exposed to light, can be redeveloped in colour developer to produce an unusual
pastel A pastel () is an art medium Arts media is the material Material is a substance Substance may refer to: * Substance (Jainism), a term in Jain ontology to denote the base or owner of attributes * Chemical substance, a material with a defi ...

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

In amateur processing, the film is removed from the
camera A camera is an optical Optics is the branch of physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and t ...

camera
and wound onto a
reel A reel is an object around which a length of another material (usually long and flexible) is wound for storage (usually hose A hose is a flexible hollow tube (fluid conveyance), tube designed to carry fluids from one location to another. Hos ...
in complete darkness (usually inside a
darkroom A darkroom is used to process , to make and to carry out other associated tasks. It is a room that can be made completely dark to allow the processing of the -sensitive photographic materials, including film and . Various equipment is used in ...

darkroom
with the
safelight A safelight is a light source Light or visible light is electromagnetic radiation In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , i ...
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, central 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
minilab A minilab is a small photographic developing and printing system or machine, as opposed to large centralized photo developing labs. Many retail stores use film or digital minilabs to provide on-site photo finishing services. With the increase in ...
s to develop films and make prints on the spot automatically without needing to send film to a remote, central 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 A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ultimately composed of atoms, which ...
and
biological Biology is the natural science Natural science is a branch of science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific method, builds and Taxonomy (general), organizes knowl ...
oxygen demand (COD and BOD). These chemical wastes are often treated with
ozone Ozone (), or trioxygen, is an inorganic molecule A molecule is an electrically Electricity is the set of physical phenomena associated with the presence and motion Image:Leaving Yongsan Station.jpg, 300px, Motion involves a cha ...

ozone
,
peroxide Peroxides are a group of compounds with the structure R−O−O−R, where R = any element. The O−O group in a peroxide is called the peroxide group or peroxo group. The nomenclature is somewhat variable. The most common peroxide is hydrogen ...

peroxide
or
aeration Aeration (also called aerification or aeriation) is the Systems engineering process, process by which air is circulated through, mixed with or solvation, dissolved in a liquid. Aeration of liquids Methods Aeration of liquids (usually water) is ach ...

aeration
to reduce the COD in commercial laboratories. Exhausted fixer and to some extent rinse water contain silver
thiosulfate Thiosulfate () (IUPAC-recommended spelling; sometimes thiosulphate in British English) is an Sulfur oxoacid, oxyanion of sulfur. The prefix thio- indicates that the thiosulfate ion is a sulfate ion with one oxygen replaced by sulfur. Thiosulfate h ...
complex ions. They are far less toxic than free silver ion, and they become
silver sulfide Silver is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

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 Ethylenediaminetetraacetic acid (EDTA) is an aminopolycarboxylic acid left, 120px, a metal complex with the EDTA anion file:Asparaginsäure - Aspartic acid.svg, 120px, Aspartic acid is an aminodicarboxylic acid and precursor to other ligands. An ...

EDTA
,
DTPA Pentetic acid or diethylenetriaminepentaacetic acid (DTPA) is an aminopolycarboxylic acid consisting of a diethylenetriamine backbone with five carboxymethyl groups. The molecule can be viewed as an expanded version of EDTA and is used similarl ...
, NTA and
borate Borates are boron-oxygen compounds, which form boron oxyanions. These can be wikt:trigon, trigonal or tetrahedron, tetrahedral in structure, or more loosely can consist of chemical mixtures which contain borate anions of either description. The e ...
. EDTA, DTPA, and NTA are very often used as
chelating agent Chelation is a type of bonding of ions and molecules to metal ions. It involves the formation or presence of two or more separate coordinate bonds between a Denticity, polydentate (multiple bonded) ligand and a single central metal atom. These l ...
s 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 Biodegradation is the breakdown of organic matter Organic matter, organic material, or natural organic matter refers to the large source of Carbon compounds, carbon-based compounds found within natural and engineered, terrestrial, and aquatic ...
, 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 Surfactants are compounds that lower the surface tension Surface tension is the tendency of liquid surfaces at rest to shrink into the minimum surface area possible. Surface tension is what allows objects with a higher density than wate ...

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 Potassium ferricyanide is the chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held tog ...

potassium ferricyanide
. This compound decomposes in the waste water stream to liberate
cyanide A cyanide is a chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held together by che ...

cyanide
gas. Other popular bleach solutions use
potassium dichromate Potassium dichromate, , is a common inorganic compound, inorganic chemical reagent, most commonly used as an oxidizing agent in various laboratory and industrial applications. As with all hexavalent chromium compounds, it is acutely and chronically ...

potassium dichromate
(a
hexavalent chromium Hexavalent chromium (chromium(VI), Cr(VI), chromium 6) is chromium Chromium is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is ...
) or
permanganate A permanganate is the general name for a chemical compound containing the manganate(VII) ion, , the conjugate base of permanganic acid. Because the manganese atom is in the +7 oxidation state, the permanganate(VII) ion is a strong oxidizing agent ...

permanganate
. Both ferricyanide and dichromate are tightly regulated for sewer disposal from commercial premises in some areas.
Borate Borates are boron-oxygen compounds, which form boron oxyanions. These can be wikt:trigon, trigonal or tetrahedron, tetrahedral in structure, or more loosely can consist of chemical mixtures which contain borate anions of either description. The e ...
s, such as
borax Borax, also known as sodium borate, sodium tetraborate, or disodium tetraborate, is an important boron chemical substance, compound, a mineral, and a salt (chemistry), salt of boric acid. Powdered borax is white, consisting of soft colorless c ...

borax
(sodium tetraborate),
boric acid Boric acid, also called hydrogen borate, boracic acid, and orthoboric acid is a weak, monobasic Lewis acid A Lewis acid (named for the American physical chemist Gilbert N. Lewis) is a chemical species that contains an empty orbital which is ...

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
hydroxylated In chemistry, hydroxylation is can refer to: *(i) most commonly, hydroxylation describes a chemistry, chemical process that introduces a hydroxyl group (-OH) into an organic compound. *(ii) the ''degree of hydroxylation'' refers to the number of O ...
benzene Benzene is an organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ (anatomy), organ Chemistry * Organic matter, matter that has come from a once-living organ ...

benzene
compounds or aminated benzene compounds, and they are harmful to humans and experimental animals. Some are
mutagen In genetics, a mutagen is a physical or chemical agent that permanently changes genetic material, usually DNA Deoxyribonucleic acid (; DNA) is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pent ...
s. They also have a large chemical oxygen demand (COD).
Ascorbic acid Vitamin C (also known as ascorbic acid and ascorbate) is a vitamin A vitamin is an organic molecule , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carb ...

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 Formaldehyde ( , also ) (systematic nameA systematic name is a name given in a systematic way to one unique group, organism, object or chemical substance A chemical substance is a form of matter In classical physics and general chemist ...
.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) Fogging in photography Photography is the 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 ...
*
Darkroom A darkroom is used to process , to make and to carry out other associated tasks. It is a room that can be made completely dark to allow the processing of the -sensitive photographic materials, including film and . Various equipment is used in ...

Darkroom
*
Cross processing Cross processing (sometimes abbreviated to Xpro) is the deliberate processing of photographic Photography is the art, application, and practice of creating durable image An SAR radar imaging, radar image acquired by the SIR-C/X-SAR rada ...
* 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