Photographic developer
Encyclopedia
In the processing of photographic films
, plates or papers, the photographic developer (or just developer) is a chemical that makes the latent image
on the film or print visible. It does this by reducing
the silver halide
s that have been exposed to light to elemental silver
in the gelatine matrix. As a generalisation, the longer a developer is allowed to work, the greater the degree of reduction of the silver halide crystals to silver
and therefore the darker the image.
Very soon more successful agents came into use such as salts of iron such as iron oxalate
, iron sulfate
and iron lactate as in the ferrotype, wet plate
and ambrotype
processes.
(monomethyl-p-aminophenol hemisulfate), Phenidone
(1-phenyl-3-pyrazolidinone) or Dimezone (4,4-dimethyl-1-phenylpyrazolidin-3-one) and hydroquinone
(benzene-1,4-diol). These are made up in aqueous solution with a suitable alkaline agent such as sodium carbonate
, borax
, or sodium hydroxide to create the appropriately high pH
and with sodium sulfite
to delay oxidation of the developing agents by atmospheric oxygen
. Hydroquinone is superadditive with metol, meaning that it acts to "recharge" the metol after it has been oxidised in the process of reducing silver in the emulsion. Sulfite in a developer not only acts to prevent aerial oxidation of the developing agents in solution, it also facilitates the regeneration of metol by hydroquinone (reducing compensation and adjacency effects) and in high enough concentrations acts as a silver halide solvent.
Most developers also contain small amounts of potassium bromide
to modify and restrain the action of the developer to suppress chemical fogging. Developers for high contrast work have higher concentrations of hydroquinone and lower concentrations of metol and tend to use strong alkali
s such as sodium hydroxide to push the pH up to around pH 11 to 12.
Metol is difficult to dissolve in solutions of high salt content and instructions for mixing developer formulae therefore almost always list Metol first. It is important to dissolve chemicals in the order in which they are listed. Some photographers add a pinch of sodium sulfite before dissolving the Metol to prevent oxidation, but large amounts of sulfite in solution will make it very slow for Metol to dissolve.
Because Metol is relatively toxic and can cause skin sensitisation, modern commercial developers often use phenidone
or Dimezone S (4-hydroxymethyl-4-methyl-1-phenyl-3-pyrazolidone) instead. Hydroquinone can also be toxic to the human operator as well as environment; some modern developers replace it with ascorbic acid
, or vitamin C. This, however, suffers from poor stability. Ascorbate developers may have the advantage of being compensating and sharpness-enhancing, as oxidation by-products formed during development are acidic, meaning they retard development in and adjacent to areas of high activity. This also explains why ascorbate developers have poor keeping properties, as oxidised ascorbate is both ineffective as a developing agent and lowers the pH of the solution, making the remaining developing agents less active. Recently, claims for practical methods to improve the stability of ascorbate developers have been made by several experimenters.
Other developing agents in use are p-aminophenol, glycin
(N-(4-hydroxyphenyl)glycine), pyrogallol
and catechol. When used in low sulfite developer composition, the latter two compounds cause gelatin to harden and stain in the vicinity of developing grains. Generally, the optical density of the stain increases in the heavily exposed (and heavily developed) area. This is a property that is highly sought after by some photographers because it increases negative contrast in relation to density, meaning that highlight detail can be captured without "blocking" (reaching high enough density that detail and tonality are severely compromised). Hydroquinone shares this property. However, the staining effect only appears in solutions with very little sulfite, and most hydroquinone developers contain substantial quantities of sulfite.
In the early days of photography, a wide range of developing agents were used, including chlorohydroquinone, ferrous oxalate, hydroxylamine
, ferrous lactate
, ferrous citrate, Eikonogen, atchecin, antipyrin, acetanilid and Amidol
(which unusually required mildly acidic conditions).
Developers also contain water softening agent to prevent calcium scum formation (e.g., EDTA salts, sodium tripolyphosphate, NTA salts, etc.).
The original lithographic developer was based upon a low sulfite/bisulfite developer with formaldehyde(added as the powder paraformaldehyde). The very low sulfite, high hydroquinone and high alkalinity encouraged "infectious development"(exposed developing silver halide crystals collided with unexposed silver halide crystals, causing them to also reduce) which enhanced the edge effect in line images. These high energy developers had a short tray life, but when used within their tray life provided consistent usable results.
Modern lithographic developers contain hydrazine compounds, tetrazolium compounds and other amine contrast boosters to increase contrast without relying on the classic hydroquinone-only lithographic developer formulation. The modern formulae are very similar to rapid access developers (except for those additives) and therefore they enjoy long tray life. However, classic lithographic developers using hydroquinone alone suffers very poor tray life and inconsistent results.
crystals in the emulsion to metallic silver
, but only those having latent image
centers created by action of light. The light sensitive layer or emulsion consists of silver halide crystals in a gelatin base. Two photons of light must be absorbed by one silver halide crystal to form a stable two atom silver metal crystal. The developer used generally will only reduce silver halide crystals that have an existing silver crystal. Faster exposure or lower light level films usually have larger grains because those images capture less light. Fine grain films, like Kodachrome, require more light to increase the chance that the halide crystal will absorb at least two quanta of light. The metallic silver image has dark (black) appearance. Once the desired level of reduction is achieved the development process is halted by washing in a dilute acid and then the undeveloped silver halide is removed by dissolving it in a thiosulfate solution, a process called fixing
. Most commercial film developers use a dual solution or "push"(pushes the films speed) development(compensating developer, like Diafine) procedure where the reducing agent e.g. hydroquinone solution soaks into and swells the gelatin then the film is introduced into the alkaline solution which activates (lowers reduction potential) of the developer. The areas with the most light exposure use up the tiny amount of developer in the gelatin and stop making silver crystal before the film at that point is totally opaque. The areas that received the least light continue to develop because they haven't used up their developer. There is less contrast, but time is not critical and films from several customers and different exposures will develop satisfactorily.
The time over which development takes place, and the type of developer, affect the relationship between the density of silver in the developed image and the quantity of light. This study is called sensitometry
and was pioneered by F Hurter & V C Driffield in the late 19th century.
black-and-white photography, a similar development process is used except that the reduction of silver simultaneously oxidizes the paraphenylene colour developing agent which then takes part in the production of dye-stuffs in the emulsion by reacting with the appropriate couplers. There are three distinct processes used here. The C-41 process
is used for almost all colour negative films and in this process dye couplers in the emulsion react with the oxidzed colour developing agent in the developer solution to generate the visible dyes. An almost identical process is then used to produce colour prints from films. The developing agents used are derivates of paraphenylene diamine.
In colour negative films, there are 3 types of dye couplers. There are the normal cyan, magenta and yellow dye forming couplers, but also there is a magenta coloured cyan masking coupler and a yellow coloured magenta masking coupler. These form respectively normal cyan dye, and magenta dye, but form an orange positive mask to correct colour. In addition, there is a third type of coupler called a DIR (Developer Inhibitor Release) coupler. This coupler releases a powerful inhibitor during dye formation, which affects edge effects and causes effects between layers to enhance overall image quality.
-type (E-6 process
) transparencies, the film is first processed in an unusual developer containing phenidone
and Hydroquinone-monosulfonate. This black and white developer is used for 6:00 at 100.4°F
(38°C
), with more time yielding "push" processing to increase the apparent film speed by reducing the Dmax, or maximum density. The first developer is the most critical step in Process E-6. The solution is essentially a black-and-white film developer, because it forms only a negative silver image in each layer of the film; no dye images are yet formed. Then, the film goes directly into the first wash for 2:00 at 100°F, which acts as a controlled stop bath. Next, the film goes into the reversal bath. This step prepares the film for the colour developer step. In this reversal bath, a chemical reversal agent is absorbed into the emulsion, with no chemical reaction taking place until the film enters the colour developer. The reversal process can also be carried out using 800 footcandle-seconds of light, which is used by process engineers to troubleshoot reversal bath chemistry problems.
Next, the film is developed to completion in the colour developer bath, which contains CD-3 as the colour developing agent. When film enters the colour developer, the reversal agent absorbed by the emulsion in the reversal bath chemically fogs (or "exposes") the unexposed silver halide (if it has not already been fogged by light in the previous step). The colour developer acts on the chemically exposed silver halide to form a positive silver image. However, the metallic silver image formed in the first developer, which is a negative image, is not a part of the reaction that takes place in this step. What is being reacted in this stage is the "leftover" of the negative image, that is, a positive image.
As the colour development progresses, metallic silver image is formed, but more importantly, the colour developing agent is oxidised. Oxidised colour developer molecules react with the couplers to form colour dyes in situ. Thus colour dye is formed at the site of development in each of the three layers of the film. Each layer of the film contains different couplers, which react with the same oxidised developer molecules but form different colour dyes. Next, the film goes into the pre-bleach (formerly conditioner) bath, which has a precursor of formaldehyde (as a dye preservative) and EDTA to "kick off" the bleach. Next, the film goes into a bleach solution. The bleach converts metallic silver into silver bromide, which is converted to soluble silver compounds in the fixer. During bleaching, iron (III) EDTA is changed to iron (II) EDTA (Fe+++ EDTA + Ag° + Br−→ Fe++ EDTA + AgBr) before fixing, and final wash.
The most common processing chemistry for such films is E6
, derived from a long line of developers produced for the Ektachrome
range of films.
Ektachrome papers are also available.
Standard black and white stock can also be reversal processed to give black and white slides. After 'first development,' the initial silver image is then removed (e.g. using a potassium bichromate/sulfuric acid bleach, which requires a subsequent "clearing bath" to remove the chromate stain from the film). The unfixed film is then fogged (physically or chemically) and 'second-developed'. . However the process works best with slow films such as Ilford Pan-F processed to give a high gamma. Kodak's chemistry kit for reversing Panatomic-X ("Direct Positive Film Developing Outfit") used sodium bisulfate in place of sulfuric acid in the bleach, and used a fogging developer that was inherently unstable, and had to be mixed and used within a two hour period. (If two rolls, the maximum capacity of a single pint of redeveloper, were to be processed in succession, the redeveloper had to be mixed while the first roll was in the first developer.)
for Kodachrome
films involves adding all the dyes to the emulsion during development.
In colour print development, the Cibachrome process also uses a print material with the dye-stuffs present and which are bleached out in appropriate places during developing. The chemistry involved here is wholly different from C41 chemistry; (it uses azo-dyes which are much more resistant to fading in sunlight).
Photographic processing
Photographic processing is the chemical means by which photographic film and paper is treated after photographic exposure to produce a negative or positive image...
, plates or papers, the photographic developer (or just developer) is a chemical that makes the latent image
Latent image
A latent image on photographic film is an invisible image produced by the exposure of the film to light. When the film is developed, the area that was exposed darkens and forms a visible image...
on the film or print visible. It does this by reducing
Redox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....
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...
s that have been exposed to light to elemental 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 the gelatine matrix. As a generalisation, the longer a developer is allowed to work, the greater the degree of reduction of the silver halide crystals to 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...
and therefore the darker the image.
History
At the start of photography a wide range of developing agents were experimented with including human urine.Very soon more successful agents came into use such as salts of iron such as iron oxalate
Iron oxalate
Iron forms two stable oxalates:* Ferrous oxalate, Fe* Ferric oxalate, Fe23...
, iron sulfate
Iron sulfate
Iron sulfate may refer to:*Ferrous sulphate, Iron sulfate, FeSO4*Ferric sulphate, Iron sulfate, Fe23...
and iron lactate as in the ferrotype, wet plate
Collodion process
The collodion process is an early photographic process. It was introduced in the 1850s and by the end of that decade it had almost entirely replaced the first practical photographic process, the daguerreotype. During the 1880s the collodion process, in turn, was largely replaced by gelatin dry...
and ambrotype
Ambrotype
right|thumb|Many ambrotypes were made by unknown photographers, such as this American example of a small girl holding a flower, circa 1860. Because of their fragility ambrotypes were held in folding cases much like those used for [[daguerreotype]]s...
processes.
Formula
For black-and-white photography, the developer is typically a mixture of MetolMetol
Metol is the chemical compound with the name monomethyl-p-aminophenol hemisulfate. It is a developing agent used in black & white photographic developers...
(monomethyl-p-aminophenol hemisulfate), Phenidone
Phenidone
Phenidone is an organic chemical compound whose primary use is as a photographic developer. It has five to ten times the developing power as Metol. It also has low toxicity and, unlike some other developers, does not cause dermatitis upon skin contact.Phenidone is Ilford's trademark for this...
(1-phenyl-3-pyrazolidinone) or Dimezone (4,4-dimethyl-1-phenylpyrazolidin-3-one) and hydroquinone
Hydroquinone
Hydroquinone, also benzene-1,4-diol or quinol, is an aromatic organic compound that is a type of phenol, having the chemical formula C6H42. Its chemical structure, shown in the table at right, has two hydroxyl groups bonded to a benzene ring in a para position. It is a white granular solid...
(benzene-1,4-diol). These are made up in aqueous solution with a suitable alkaline agent such as sodium carbonate
Sodium carbonate
Sodium carbonate , Na2CO3 is a sodium salt of carbonic acid. It most commonly occurs as a crystalline heptahydrate, which readily effloresces to form a white powder, the monohydrate. Sodium carbonate is domestically well-known for its everyday use as a water softener. It can be extracted from the...
, borax
Borax
Borax, also known as sodium borate, sodium tetraborate, or disodium tetraborate, is an important boron compound, a mineral, and a salt of boric acid. It is usually a white powder consisting of soft colorless crystals that dissolve easily in water.Borax has a wide variety of uses...
, or sodium hydroxide to create the appropriately high pH
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
and with sodium sulfite
Sodium sulfite
Sodium sulfite is a soluble sodium salt of sulfurous acid. It is a product of sulfur dioxide scrubbing, a part of the flue gas desulfurization process...
to delay oxidation of the developing agents by atmospheric oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
. Hydroquinone is superadditive with metol, meaning that it acts to "recharge" the metol after it has been oxidised in the process of reducing silver in the emulsion. Sulfite in a developer not only acts to prevent aerial oxidation of the developing agents in solution, it also facilitates the regeneration of metol by hydroquinone (reducing compensation and adjacency effects) and in high enough concentrations acts as a silver halide solvent.
Most developers also contain small amounts of potassium bromide
Potassium bromide
Potassium bromide is a salt, widely used as an anticonvulsant and a sedative in the late 19th and early 20th centuries, with over-the-counter use extending to 1975 in the United States. Its action is due to the bromide ion...
to modify and restrain the action of the developer to suppress chemical fogging. Developers for high contrast work have higher concentrations of hydroquinone and lower concentrations of metol and tend to use strong alkali
Alkali
In chemistry, an alkali is a basic, ionic salt of an alkali metal or alkaline earth metal element. Some authors also define an alkali as a base that dissolves in water. A solution of a soluble base has a pH greater than 7. The adjective alkaline is commonly used in English as a synonym for base,...
s such as sodium hydroxide to push the pH up to around pH 11 to 12.
Metol is difficult to dissolve in solutions of high salt content and instructions for mixing developer formulae therefore almost always list Metol first. It is important to dissolve chemicals in the order in which they are listed. Some photographers add a pinch of sodium sulfite before dissolving the Metol to prevent oxidation, but large amounts of sulfite in solution will make it very slow for Metol to dissolve.
Because Metol is relatively toxic and can cause skin sensitisation, modern commercial developers often use phenidone
Phenidone
Phenidone is an organic chemical compound whose primary use is as a photographic developer. It has five to ten times the developing power as Metol. It also has low toxicity and, unlike some other developers, does not cause dermatitis upon skin contact.Phenidone is Ilford's trademark for this...
or Dimezone S (4-hydroxymethyl-4-methyl-1-phenyl-3-pyrazolidone) instead. Hydroquinone can also be toxic to the human operator as well as environment; some modern developers replace it with ascorbic acid
Ascorbic acid
Ascorbic acid is a naturally occurring organic compound with antioxidant properties. It is a white solid, but impure samples can appear yellowish. It dissolves well in water to give mildly acidic solutions. Ascorbic acid is one form of vitamin C. The name is derived from a- and scorbutus , the...
, or vitamin C. This, however, suffers from poor stability. Ascorbate developers may have the advantage of being compensating and sharpness-enhancing, as oxidation by-products formed during development are acidic, meaning they retard development in and adjacent to areas of high activity. This also explains why ascorbate developers have poor keeping properties, as oxidised ascorbate is both ineffective as a developing agent and lowers the pH of the solution, making the remaining developing agents less active. Recently, claims for practical methods to improve the stability of ascorbate developers have been made by several experimenters.
Other developing agents in use are p-aminophenol, glycin
Glycin
Glycin, or N-glycine, is N-substituted p-aminophenol. It is a photographic developing agent used in classic B&W developer solutions. It is a derivative of the amino acid glycine. When fresh, it is typically characterized as thin plates of white or silvery powder, turning brown with age...
(N-(4-hydroxyphenyl)glycine), pyrogallol
Pyrogallol
Pyrogallol or benzene-1,2,3-triol is a benzenetriol. It is a white crystalline powder and a powerful reducing agent. It was first prepared by Scheele 1786 by heating gallic acid. An alternate preparation is heating para-chlorophenoldisulphonic acid with potassium hydroxide.When in alkaline...
and catechol. When used in low sulfite developer composition, the latter two compounds cause gelatin to harden and stain in the vicinity of developing grains. Generally, the optical density of the stain increases in the heavily exposed (and heavily developed) area. This is a property that is highly sought after by some photographers because it increases negative contrast in relation to density, meaning that highlight detail can be captured without "blocking" (reaching high enough density that detail and tonality are severely compromised). Hydroquinone shares this property. However, the staining effect only appears in solutions with very little sulfite, and most hydroquinone developers contain substantial quantities of sulfite.
In the early days of photography, a wide range of developing agents were used, including chlorohydroquinone, ferrous oxalate, hydroxylamine
Hydroxylamine
Hydroxylamine is an inorganic compound with the formula NH2OH. The pure material is a white, unstable crystalline, hygroscopic compound. However, hydroxylamine is almost always provided and used as an aqueous solution. It is used to prepare oximes, an important functional group. It is also an...
, ferrous lactate
Ferrous lactate
Ferrous lactate, or iron lactate, is a chemical compound consisting of one atom of iron and two lactate anions. It has the chemical formula Fe2. It is used as a food additive with E number E585. It is an acidity regulator and colour retention agent, and is also used to fortify foods with iron....
, ferrous citrate, Eikonogen, atchecin, antipyrin, acetanilid and Amidol
Amidol
Amidol is a colorless crystalline compound with the molecular structure C6H32OH. It is a dihydrogen chloride salt and is used as a photographic developer. It was introduced as a developing agent for photographic papers in 1892...
(which unusually required mildly acidic conditions).
Developers also contain water softening agent to prevent calcium scum formation (e.g., EDTA salts, sodium tripolyphosphate, NTA salts, etc.).
The original lithographic developer was based upon a low sulfite/bisulfite developer with formaldehyde(added as the powder paraformaldehyde). The very low sulfite, high hydroquinone and high alkalinity encouraged "infectious development"(exposed developing silver halide crystals collided with unexposed silver halide crystals, causing them to also reduce) which enhanced the edge effect in line images. These high energy developers had a short tray life, but when used within their tray life provided consistent usable results.
Modern lithographic developers contain hydrazine compounds, tetrazolium compounds and other amine contrast boosters to increase contrast without relying on the classic hydroquinone-only lithographic developer formulation. The modern formulae are very similar to rapid access developers (except for those additives) and therefore they enjoy long tray life. However, classic lithographic developers using hydroquinone alone suffers very poor tray life and inconsistent results.
Development
The developer selectively reduces silver halideSilver 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...
crystals in the emulsion to metallic 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...
, but only those having latent image
Latent image
A latent image on photographic film is an invisible image produced by the exposure of the film to light. When the film is developed, the area that was exposed darkens and forms a visible image...
centers created by action of light. The light sensitive layer or emulsion consists of silver halide crystals in a gelatin base. Two photons of light must be absorbed by one silver halide crystal to form a stable two atom silver metal crystal. The developer used generally will only reduce silver halide crystals that have an existing silver crystal. Faster exposure or lower light level films usually have larger grains because those images capture less light. Fine grain films, like Kodachrome, require more light to increase the chance that the halide crystal will absorb at least two quanta of light. The metallic silver image has dark (black) appearance. Once the desired level of reduction is achieved the development process is halted by washing in a dilute acid and then the undeveloped silver halide is removed by dissolving it in a thiosulfate solution, a process called fixing
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...
. Most commercial film developers use a dual solution or "push"(pushes the films speed) development(compensating developer, like Diafine) procedure where the reducing agent e.g. hydroquinone solution soaks into and swells the gelatin then the film is introduced into the alkaline solution which activates (lowers reduction potential) of the developer. The areas with the most light exposure use up the tiny amount of developer in the gelatin and stop making silver crystal before the film at that point is totally opaque. The areas that received the least light continue to develop because they haven't used up their developer. There is less contrast, but time is not critical and films from several customers and different exposures will develop satisfactorily.
The time over which development takes place, and the type of developer, affect the relationship between the density of silver in the developed image and the quantity of light. This study is called sensitometry
Sensitometry
Sensitometry is the scientific study of light-sensitive materials, especially photographic film. The study has its origins in the work by Ferdinand Hurter and Vero Charles Driffield with early black-and-white emulsions...
and was pioneered by F Hurter & V C Driffield in the late 19th century.
Colour development
In colour and chromogenicChromogenic
Chromogenic refers to color photographic processes in which a traditional silver image is first formed, and then later replaced with a colored dye image.- Description :...
black-and-white photography, a similar development process is used except that the reduction of silver simultaneously oxidizes the paraphenylene colour developing agent which then takes part in the production of dye-stuffs in the emulsion by reacting with the appropriate couplers. There are three distinct processes used here. The 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....
is used for almost all colour negative films and in this process dye couplers in the emulsion react with the oxidzed colour developing agent in the developer solution to generate the visible dyes. An almost identical process is then used to produce colour prints from films. The developing agents used are derivates of paraphenylene diamine.
In colour negative films, there are 3 types of dye couplers. There are the normal cyan, magenta and yellow dye forming couplers, but also there is a magenta coloured cyan masking coupler and a yellow coloured magenta masking coupler. These form respectively normal cyan dye, and magenta dye, but form an orange positive mask to correct colour. In addition, there is a third type of coupler called a DIR (Developer Inhibitor Release) coupler. This coupler releases a powerful inhibitor during dye formation, which affects edge effects and causes effects between layers to enhance overall image quality.
Reversal film development
In EktachromeEktachrome
Ektachrome is a brand name owned by Kodak for a range of transparency, still, and motion picture films available in most formats, including 35 mm and sheet sizes to 11x14 inch size. Ektachrome has a distinctive look that became familiar to many readers of National Geographic, which used it...
-type (E-6 process
E-6 process
The E-6 process is a chromogenic photographic process for developing Ektachrome, Fujichrome and other color reversal photographic film....
) transparencies, the film is first processed in an unusual developer containing phenidone
Phenidone
Phenidone is an organic chemical compound whose primary use is as a photographic developer. It has five to ten times the developing power as Metol. It also has low toxicity and, unlike some other developers, does not cause dermatitis upon skin contact.Phenidone is Ilford's trademark for this...
and Hydroquinone-monosulfonate. This black and white developer is used for 6:00 at 100.4°F
Fahrenheit
Fahrenheit is the temperature scale proposed in 1724 by, and named after, the German physicist Daniel Gabriel Fahrenheit . Within this scale, the freezing of water into ice is defined at 32 degrees, while the boiling point of water is defined to be 212 degrees...
(38°C
Celsius
Celsius is a scale and unit of measurement for temperature. It is named after the Swedish astronomer Anders Celsius , who developed a similar temperature scale two years before his death...
), with more time yielding "push" processing to increase the apparent film speed by reducing the Dmax, or maximum density. The first developer is the most critical step in Process E-6. The solution is essentially a black-and-white film developer, because it forms only a negative silver image in each layer of the film; no dye images are yet formed. Then, the film goes directly into the first wash for 2:00 at 100°F, which acts as a controlled stop bath. Next, the film goes into the reversal bath. This step prepares the film for the colour developer step. In this reversal bath, a chemical reversal agent is absorbed into the emulsion, with no chemical reaction taking place until the film enters the colour developer. The reversal process can also be carried out using 800 footcandle-seconds of light, which is used by process engineers to troubleshoot reversal bath chemistry problems.
Next, the film is developed to completion in the colour developer bath, which contains CD-3 as the colour developing agent. When film enters the colour developer, the reversal agent absorbed by the emulsion in the reversal bath chemically fogs (or "exposes") the unexposed silver halide (if it has not already been fogged by light in the previous step). The colour developer acts on the chemically exposed silver halide to form a positive silver image. However, the metallic silver image formed in the first developer, which is a negative image, is not a part of the reaction that takes place in this step. What is being reacted in this stage is the "leftover" of the negative image, that is, a positive image.
As the colour development progresses, metallic silver image is formed, but more importantly, the colour developing agent is oxidised. Oxidised colour developer molecules react with the couplers to form colour dyes in situ. Thus colour dye is formed at the site of development in each of the three layers of the film. Each layer of the film contains different couplers, which react with the same oxidised developer molecules but form different colour dyes. Next, the film goes into the pre-bleach (formerly conditioner) bath, which has a precursor of formaldehyde (as a dye preservative) and EDTA to "kick off" the bleach. Next, the film goes into a bleach solution. The bleach converts metallic silver into silver bromide, which is converted to soluble silver compounds in the fixer. During bleaching, iron (III) EDTA is changed to iron (II) EDTA (Fe+++ EDTA + Ag° + Br−→ Fe++ EDTA + AgBr) before fixing, and final wash.
The most common processing chemistry for such films is E6
E-6 process
The E-6 process is a chromogenic photographic process for developing Ektachrome, Fujichrome and other color reversal photographic film....
, derived from a long line of developers produced for the Ektachrome
Ektachrome
Ektachrome is a brand name owned by Kodak for a range of transparency, still, and motion picture films available in most formats, including 35 mm and sheet sizes to 11x14 inch size. Ektachrome has a distinctive look that became familiar to many readers of National Geographic, which used it...
range of films.
Ektachrome papers are also available.
Standard black and white stock can also be reversal processed to give black and white slides. After 'first development,' the initial silver image is then removed (e.g. using a potassium bichromate/sulfuric acid bleach, which requires a subsequent "clearing bath" to remove the chromate stain from the film). The unfixed film is then fogged (physically or chemically) and 'second-developed'. . However the process works best with slow films such as Ilford Pan-F processed to give a high gamma. Kodak's chemistry kit for reversing Panatomic-X ("Direct Positive Film Developing Outfit") used sodium bisulfate in place of sulfuric acid in the bleach, and used a fogging developer that was inherently unstable, and had to be mixed and used within a two hour period. (If two rolls, the maximum capacity of a single pint of redeveloper, were to be processed in succession, the redeveloper had to be mixed while the first roll was in the first developer.)
Proprietary methods
The K-14 processK-14 process
K-14 was the developing process for Kodak's Kodachrome transparency film; the last version having been designated Process K-14M. The process differed significantly from its contemporary, the E-6 process, in both complexity and length. Kodachrome film has no integral color couplers; dyes are...
for Kodachrome
Kodachrome
Kodachrome is the trademarked brand name of a type of color reversal film that was manufactured by Eastman Kodak from 1935 to 2009.-Background:...
films involves adding all the dyes to the emulsion during development.
In colour print development, the Cibachrome process also uses a print material with the dye-stuffs present and which are bleached out in appropriate places during developing. The chemistry involved here is wholly different from C41 chemistry; (it uses azo-dyes which are much more resistant to fading in sunlight).