In film developing, photographic developer (or just developer) is a chemical that makes the latent image on the film or print visible. Photographic processing is the Industrial process by which conventional Photographic film is treated after Photographic exposure in order to produce the A latent image on Photographic film is an invisible image produced by the exposure of the film to Light. It does this by reducing the silver halides that have been exposed to light to metals of elemental silver in the gelatine matrix. Silver (ˈsɪlvɚ is a Chemical element with the symbol " Ag " (argentum from the Ancient Greek: ἀργήντος - argēntos gen 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.
Contents |
Formula
For black and white photography, the developer is often a mixture of Metol, Phenidone or Dimezone and hydroquinone. Metol is a developing agent used in b&w Photographic developers In its pure form it is a Solid rather light-sensitive Chemical which is the half Phenidone (1-phenyl-3-pyrazolidinone is an organic chemical compound whose primary use is as a Photographic developer. Hydroquinone, also benzene-14-diol or quinol, is an Aromatic Organic compound which is a type of phenol, having the Chemical These are made up in aqueous solution with a suitable alkaline agent such as sodium carbonate, borax, etc. Sodium carbonate (also known as washing soda or soda ash), is a Sodium Salt of Carbonic acid. Borax (from Persian burah) also known as sodium borate, sodium tetraborate, or disodium tetraborate, is an important Boron to create the appropriately high pH and with sodium sulfite to delay oxidation of the developing agents by atmospheric oxygen. pH is the measure of the acidity or alkalinity of a Solution. Sodium sulfite (sodium sulphite is a soluble compound of Sodium. Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the 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. Potassium bromide ( K[[Bromine Br]] is a salt, widely used as an Anticonvulsant and a Sedative in the late 19th and early 20th centuries Developers for high contrast work have higher concentrations of hydroquinone and lower concentrations of metol and tend to use strong alkalis such as sodium hydroxide to push the pH up to around pH 11 to 12. In Chemistry, an alkali (from Arabic: Al-Qaly القلي القالي) is a basic, ionic salt of an Alkali metal Sodium hydroxide ( Na[[hydroxide OH]]) also known as Lye, caustic soda and (incorrectly according to IUPAC nomenclature
Because Metol is difficult to dissolve in solutions of high salt content, instructions for mixing developer formulae 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 instead. Phenidone (1-phenyl-3-pyrazolidinone is an organic chemical compound whose primary use is as a Photographic developer. 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 article deals with the molecular aspects of ascorbic acid 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. Glycin, or N-(4-hydroxyphenylglycine is N-substituted p-aminophenol Pyrogallol or benzene-123-triol is a white crystalline powder and a powerful reducing agent Pyrocatechol, more commonly known as catechol, is the Organic compound with the formula C6H4(OH2 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). Hydroxylamine is a reactive chemical with formula NH2OH It can be considered a hybrid of Ammonia and Water due to parallels it shares Ferrous lactate, or iron(II lactate, is a chemical compound consisting of one atom of iron (Fe2+ and two lactate anions. Phenazone, or phenazon, is an Analgesic. It was first synthesised by Ludwig Knorr in 1883 Acetanilide is an odourless Solid chemical of leaf or flake-like appearance Amidol is a colorless Crystalline compound with the molecular structure C6H3(NH22OH
Developers also contain water softening agent to prevent calcium scum formation (e. g. , EDTA salts, sodium tripolyphosphate, NTA salts, etc. ).
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 halide crystals in the emulsion to metallic silver, but only those having latent image centers created by action of light. A silver halide is one of the compounds formed between Silver and one of the Halogens &mdash Silver bromide (AgBr chloride Silver (ˈsɪlvɚ is a Chemical element with the symbol " Ag " (argentum from the Ancient Greek: ἀργήντος - argēntos gen A latent image on Photographic film is an invisible image produced by the exposure of the film to Light. The metallic silver image has dark (black) appearance and is opaque. The image is then fixed using photographic fixer. Photographic fixer is a chemical used in the final step in the Photographic processing of film or paper
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 1800s. Sensitometry is the scientific study of light-sensitive materials especially Photographic film.
Colour development
In colour and chromogenic 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. Chromogenic refers to color Photographic processes in which a traditional silver image is first formed and then later replaced with a colored Dye image 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. C-41 is a 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 Dye coupler is present in Chromogenic film and paper used in Photography, primarily color photography 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 Ektachrome-type (E-6 process) transparencies, the film is first processed in an unusual developer containing phenidone and Hydroquinone-monosulfonate. Ektachrome is a brand name owned by Kodak for a range of transparency still and motion picture films available in most formats including The E-6 process (often abbreviated to just E-6) is a Photographic processing system for developing Ektachrome, Fujichrome, and other color 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. Fahrenheit is a temperature scale named after Daniel Gabriel Fahrenheit (1686–1736 a German Physicist who proposed it in 1724 The Celsius Temperature scale was previously known as the centigrade scale. 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. (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. That is, 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. The E-6 process (often abbreviated to just E-6) is a Photographic processing system for developing Ektachrome, Fujichrome, and other color Ektachrome is a brand name owned by Kodak for a range of transparency still and motion picture films available in most formats including
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'. (See say M J Langford Advanced Photography Focal Press (1980) p345 for materials details; kits containing the necessary fogging and bleach agents are also available commercially). However the process works best with slow films such as Ilford Pan-F processed to give a high gamma. Gamma correction, gamma nonlinearity, gamma encoding, or often simply gamma, is the name of a nonlinear operation used to code and decode luminance 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 process for Kodachrome films involves adding all the dyes to the emulsion during development. K-14 is the developing process for Kodak 's Kodachrome transparency film Kodachrome is the trademarked name of a brand of color reversal film sold by Eastman Kodak.
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. Ilfochrome, (formerly known as Cibachrome) is a Dye destruction positive-to-positive photographic process used for the reproduction of Slides on Photographic The chemistry involved here is wholly different from C41 chemistry; (it uses azo-dyes which are much more resistant to fading in sunlight).
Early processes
Primitive processes (i. e. ferrotype, wet plate, ambrotype) use ferro sulfate to oxidise silver. Tintype, also melainotype and ferrotype, is a Photographic process first described by Adolphe-Alexandre Martin in France in 1853 and patented The collodion process is an early photographic process which was quickly replaced at the end of the 19th century with today's gelatin emulsion process The ambrotype process (from Greek ambrotos, "immortal" or amphitype is a photographic process that creates a positive photographic Most silver-based emulsions need to oxidise the free silver in it to form an image.
The chemical process can be described as ferro sulfate splitting into iron and sulfurous acid leaving a radical oxygen molecule that combines with the silver forming silver oxide.
Dapyx Software network: MP3 Explorer | Ebook Manager | Zenithic