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Development or Processing is a photographic process in which the latent image contained in film or paper after exposure is converted into a visible and permanent image.

Photography, since its invention, relied on metallic salts (silver, iron, etc) that were affected by light. In the 17th century Angelo Sala, an Italian scientist, reported that silver nitrate became black when exposed to light. Silver salts react to light in a predictable manner, the more exposure, the darker they become. This is applied into film or glass plates, which after exposure need to be developed.

Daguerreotypes, the first commercial photographic processes, were made with silver-coated copper plates; which were "sensitized" with iodine crystals (creating Ag-I crystals). After exposing to light the plate was exposed to Mercury vapors until the image was visible and then washed in a Sodium Thiosulfate solution. [1]

Further processes evolved and abandoned the use of mercury. However, development of images, both in film and paper is mostly a chemical process. The processing of film and papers consist normally of a few steps: Developer, Stop Bath, Fixing, Washing, and Stabilization. These processes are carried out in a Darkroom, which can be as small as a changing bag, where light is blocked to prevent further exposure and the where film and paper are processed.

The initial results is generally a negative, with the exception of Reversal processing which ends in a direct positive. In many cases positives are obtained by making a negative of a negative, which yields a positive such as in enlarging.

Some processes also include toning, either for color change or for improved permanence.[2]

As of 2022 there are many labs that still do chemical processes, and a non-exhaustive list is compiled.


Chemical development is the most common method, and involves chemical agents that are mixed to produce the working solutions. Many chemicals can be bought in pre-mixed packages, either solid or liquid for use by the photographer. Several of these formulas have been published, and can be found online or in books, but most are proprietary.

Chemicals must be handled with caution, the use of eye and skin protection is very important, as well as good ventilation in the space.

Water is the most important chemical used in development, impurities present in water might interfere with development and must be compensated for. Among others, Iron, Copper and other metallic impurities interfere with chemicals, hardness can cause water marks during drying, and suspended solids might deposit on the image creating spots. Potable water is generally acceptable for processing; however for the preparation of concentrated solutions distilled or deionized water is sometimes recommended.

Black and White Development

Black and white images are made by converting the exposed silver halide crystals to metallic silver. Each of the small crystals will become a grain. Developer-film combinations, have characteristics which either separately or combined affect the quality of the image which includes sharpness, contrast, graininess and resolving power. This is especially important when developing negatives, where the basis of the image is formed, and good quality prints can't be made form poor quality negatives. All these qualities are affected by the development procedure and chosen developer.[3][4]

  • Accutance: is a measure of the resolving power and sharpness of an image.
  • Graininess: While grain is an inherent characteristic of film, historically faster films had larger grain, but modern film (T-max, Ilford Delta, Fuji Acros) use oriented crystals in which the grain size is more or less uniform. Graininess is the perception of this grain by the final observer, and depends on the final grain pattern on the negative, whether it is tight, fuzzy, soft or hard edged.
  • Speed: measures the sensitivity of the film, and how it reacts to light. The faster the film the less light it needs to have images in the thinnest parts.
  • Contrast: Is a measure of the differences between dark and light areas on an image, wither in macro scale or in micro scale. Micro-contrast has an effect on how the details of the image can be captured when there are differences in luminosity. Macro-contrast tells how easy a negative is to "print" or which paper grade it needs.

Chemistry for BW development is relatively simple, the chemicals that are used for developing are listed below [5][6][7][8]


Developer is a mixtures of chemicals that converts the latent image into metallic silver. The combination of developer, exposure, agitation and temperature affect the final image and must be considered,

Developers can be formulated to affect the image quality and are usually categorized as solvent/non-solvent, or increase/decrease speed. The balance between the negative characteristics and the developer used change the final image quality and are part of the art of producing a good negative.

Developers are made of four basic components:

  • Developing agent: a chemical compound that reduces silver halides that have been exposed to light to metallic silver. The agent determines the film speed, graininess, sharpness (accutance) and contrast.
    Several developing agents have ben used through history and the most common are:
    • Hydroquinone (Q)
    • Metol (M) or Elon, sulfate salt of N-methylaminophenol
    • Phenidone (P)
    • Glycin - for warm tone developers
    • Amidol - for high temperature developers
    • Pyrogallic Acid (Pyro)
    • para-amino-phenol, acive ingredient of the oldest commercial developer, Rodinal
    • Pyrocathechin (Catechol)
    • para-Phenylenediamine (PPD)
    • Ascorbic acid (vitamin C)

Some of this agents have unique characteristics and mixtures of them have been tested for increased development activity (super additivity). Supper additivity of Metol-Hydroquinone (MQ), PQ, PC, and other combinations has been used for commercial developers. The last agent to be exploited commercially was Ascorbic Acid, with several developers coming in the late 90s and early 2000s (Kodak Xtol, Ilfotec DDX)

  • Preservative: to reduce the oxidation of the developing agent and extend the life of the solutions. These agents prevent oxygen in the air from making the developer useless too quickly.
    • Sodium sulfite. Sodium sulfite in large enough concentration is also a accelerator and a silver solvent, and it is thus used for most fine-grain developers.
    • Sodium bisulfite is used in addition to sulfite to create a buffer and increase the sulfite action.

Potassium salts can also be used but that is less common

  • Accelerator: A compound that increases the activity of the development by changing pH or REDOX potential without being a developer itself.

Alkaline pH helps in increasing the development activity and reducing the time needed from hours to minutes. Depending on the final pH there are mild (pH 8-10), moderate (pH 10-11) or strong alkalis (pH>11). The strongest the alkali the faster the developer action, the coarser the grain, and the contrast that is attained. In many cases buffer solutions are used to ensure that the pH is fairly constant during the life of the developer.

    • Mild Alkalis: Borax, balanced alkali (Kodalk)
    • Moderate Alkalis: Sodium (potassium) carbonate
    • Strong alkalis: Sodium (potassium) hydroxide

  • Restrainer: compounds that prevent the formation of "fog" in the image, i.e. that only the part of the image that was exposed gets reduced to silver.
    • Potassium bromide
    • Potassium iodide
    • Benzotriazole (BZT)

Some other chemicals might be used in the formulation of developers, such as water softeners and chelating agents to prevent the ions present in water to interfere with development or wetting agents to help with elimination of anti-halation layers or dyes.

Developer concentrates maybe be made with solvents other than water, which prevent oxidation and extend the shelf life, Triethanolamine, Propyl-glycol, etc.

Developers can be a single solution, or a double solution which is called Divided developers. Divided developers separate the developer agent from the accelerant, i.e. solution A contains the developer agent, restrainer and preservative and solution B contain alkali and restrainer. The film is first dipped in solution A, t absorb developer agent, and then solution B, where the developer is exhausted quickly in the dark regions, with the advantage of having better contrast control, preventing over development and increasing details in the thin areas and definition. [6]

Commercial developers

Several commercial developers have been used effectively and some can still be acquired either as powder or liquid formulas. Published formulas can be easily categorized by company by noting that D or DK is Kodak, ID is Ilford, FX or ACU are Paterson, while AGFA/Ansco, Dupont, and others didn't use prefixes. [9]

Several famous developers are:

  • AGFA Rodinal, Rodinal Special, Studional
  • Kodak D1 (Pyro), D23, D76, HC110, Microdol-X, Xtol
  • Ilford ID11, ID110, Ilsofol, Ilfotec DD-X
  • DuPont 1D, 2D, 5D
  • Paterson/ADOX Geoffrey Crawley's Acutol, FX-39, FX-7
  • Edwal 20 and FG-7
  • TETENAL Neofin Blue and Red
  • Diafine

Stop Bath

In order to stop development, a stop bath of a mild acid is used. Acetic or citric acid solutions are used, however this must be weak to avoid the formation of CO2 bubbles which can create pinholes in the emulsion. Water can also be sued as a stop bath


Fixation is a critical step in making images permanent. Fixation must remove the unexposed light sensitive compounds while not damaging the image that is already formed.

There are 3 types of fixer, depending on the pH of the bath: neutral, acid and alkaline.

The most common fixing agents are thiosulphate (Hypo or hyposulfite) compounds, plain Sodium Thiosulphate was used for many decades, but its action is relatively slow and it is affected by the alkali that is carried over from the developer and exhausted quickly by iodine salts used in modern films. Ammonium Thiosulphate is much faster and efficient for modern emulsions (1980s onwards) that use iodine compounds. Acid can be added to the fixer to extend its life, but carefully so as not to precipitate the sulfur (cloud the fixer).

Alkaline fixers are easier to wash from film and paper and can't over fix.

Acid that is added to fixer must be a weak acid, such as acetic mixed with sulfite or bisulfite as preservatives.

Hardener compounds were added to fixer, to make the wet emulsion harder and prevent scratching.. These are not needed with modern emulsions.


Any remaining fixing salts will damage the photographic emulsion, and several stabilizing solutions exist. These stabilizers are used either before washing the print (HCA or Berg Bath) or as final no-rinse steps (Sistan)

    • Hypo Clearing Agent (HCA)
    • Sistan (trademark of AGFA), currently and improved versin is made by Adox as Adostab
    • Ag-Guard (trademark of FujiFilm)
    • Berg Bath (trademark or Berg chemicals)


After fixing it is very important to wash away all remaining fixer, by-products and silver compounds from the emulsion, this ensures longevity of the images. Washing also carries away the sensitizing dyes that are used in films to make them sensitive to the whole spectrum of light.

Several methods of washing exist, either using running water or by changing water in the small developing tanks. Thorough washing is highly recommended.

As final step of washing a wetting agent (Kodak Photo-Flo, Edwal LPN or similar) is used to prevent the formation of drop marks while drying. In lieu of a wetting agent, deionized water can be used for the final rinse.

Other Chemicals

Specialty chemical solutions, such as intensifier, reducers, and bleachers are used occasionally.


Darkroom is a room isolated from sunlight, where the development process is carried out. Depending on the type of process it can be as small as a changing bag, or as large as a whole newspaper floor. It must be kept clean and have good ventilation. Commercial film processing machines essentially act as self-contained darkrooms, where the whole process is carried out in a small space.

Paper positives are made in the darkroom, by enlarging and development of the paper. During enlargement of Black and White paper a safelight can be used, due to paper being sensitive only to blue and green light. Safelights are units which filter the blue and green parts of the spectrum, traditionally they used RED filters; but amber has replaced them. Safelights can also be used for orthocromatic plates and film and non-silver based processes such as cyanotype

Film and plates

Film is usually loaded into tanks that can be used on full light (daylight tanks); these tanks are either plastic or metallic and are fitted with aprons or spirals that allow the flow of chemicals and prevent each turn form touching the next.

Plates are either developed in trays or in tanks, with a rack system to keep plates separated and allow the flow of chemicals.


Photographies are captured in film, which can be a small image. Those images can be printed using an Enlarger by projecting the image onto paper.[10] The projection is then exposed in light sensitive paper of different grades and qualities. Paper can have either a plastic base (resin coated) or a baryta base, and it can be single grade or multigrade. Multigrade paper is made by having 2 emulsions concurrently, one soft and one hard contrast, which have different sensitivities to light frequencies, the paper is exposed using light with color filters ti determine the final contrast.

Once the image has been projected, the paper needs to be developed following the same steps. Papers for BW are usually not sensitive to red light, and can be thus developed in trays with a safelight, while color papers needs to be developed in light tight tanks or closed processors.

Papers are subject to toning to change the color and to increase the permanence of the image.

Color Development

Color film has been available since the 1930s, and it is based on different light sensitive couplers and silver. Development of these films follows similar steps to Black and White. However the chemicals used help develop the chromogenic layers, leaving only dyes behind. A step to remove the silver is also incorporated in the development of color images. This bleaching step is in many cases part of the fix step, thus called Blix

Reversal Development

Reversal development produces a positive directly from the exposed film. While this is common in color slides, with Kodachrome introduced in 1934.

Black and white reversal is less common; and only a few films are suitable for this process. Reversal development process requires that film has more silver than normal films. After the first developer, a bleach step is performed to wash away the negative silver image. The silver halide grains left behind are then exposed to light or receive a chemical fogging process which produces a negative of a negative (i.e. a positive); a second developer stage is then applied followed by fixing.

Commercially AGFA introduced Scala film. In 1998 David Wood started dr5 chrome lab, with a proprietary process that produced black and white slides from a large number of films. This lab was closed in 2022.

Color film reversal is described in detail the E-6 process page.


Laboratories that still process films in different parts of the world can be added here. This list tries not to be exhaustive but will be extended as we know more of them.


North America


  1. Light and Film. LIFE Encyclopedia of Photography. 1971
  2. Eastman Kodak Company. 1966. Kodak Master Darkroom Dataguide. Kodak Publication R-20.
  3. Horenstein H. 2005. Black and White Photography, A Basic Manual. 3rd Ed. Little Brown and Co. NY
  4. Mason, l.J.A.. 1966. Photographic Processing Chemistry. Focal Press. NY ISBN:0240506332
  5. Anchell S.G. 2000. Darkroom Cookbook. Focal Press NY
  6. 6.0 6.1 Anchell S.G., Troop B. 2020. The Film Development Cookbook, 2nd ed. Focal PRess NY
  7. Elementary Photographic Chemistry. Eastman Kodak Company. 1934. Rochester NY
  8. Eastman Kodak Company. 1963. Processing Chemicals and Formulas. Kodak Professional Data Book J-1
  9. Haist G. 1979. Modern Photographic Processing . John Wiley and Sons. NY ISBN:0471042862
  10. Eastman Kodak Company. 1967. Enlarging in Black and White and Color. Kodak Photo Information Book AG-16


  • Beutler, W. 1978. Meine Dunkelkammer-Praxis 6th ed. Knapp Verlag, Dusseldorf. ISBN: 3874201058
  • Coote, J.H. 1988 Ilford Monochrome Darkroom Practice 2nd ed. Focal Press. London ISBN: 9780240512624 at the internet archive
  • Haist, G. 1979. Modern Photographic Processing . John Wiley and Sons. NY ISBN:0471042862 at the Internet archive
  • Horenstein, H. 2005. Black and White Photography, A Basic Manual. 3rd Ed. Little Brown and Co. NY
  • Jacobson C.I. 1970 Developing: the negative technique 17th ed. Focal Press, London. at the internet archive
  • Mason, l.J.A. 1966. Photographic Processing Chemistry. Focal Press. NY ISBN:0240506332
  • Mees, C.E.K. 1946. The theory of Photographic Processes. MacMillan Co. NY
  • Rogers, D.N. 2006. The Chemistry Of Photography: From Classical To Digital Technologies. Royal Society of Chemistry, London. ISBN: 0854042733
  • VEB Filmfabrik AGFA Wolfen. 1960 AGFA-Rezepte und -Packungen. VEB Leipzig. (Easter germany Agfa/ORWO)
  • AGFA-ANSCO 1941. Agfa Formulas for Photographic use. AGFA-ANSCO COmpany. Binghamton, NY
  • Dickerson D. and Zawadzki S. 1999. The Genesis of Xtol. Photo Techniques Magazine Vol 20(5) pp 62-66