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Superadditive Developer
Photographic developer solutions may contain more than one developing agents, such as Metol and hydroquinone, or Phenidone and hydroquinone. This is because they work together to a synergistic effect, called superadditive development. Definition Superadditive development commonly means that the mathematical superadditive inequality holds for the rate of development. That is, the rate of development of the two (or more) agents together is greater than the sum of the rate of each agent used alone. There are cases that ''density'' superadditivity holds without ''rate'' superadditivity. Note that the term superadditive development is usually ''not'' used to mean density superadditivity: the image density obtained from the combined agents is greater than the sum of the density from each agent used alone. Mechanism There were several historical theories about the mechanism of superadditive development, until G. I. P. Levenson elucidated the regeneration mechanism. It is useful to re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Metol
Metol (or Elon) is a trade name for the organic compound with the formula OC6H4NH2(CH3)SO4. It is the sulfate salt of ''N''-methylaminophenol. This colourless salt is a popular photographic developer used in black & white photography.Gerd Löbbert "Photography" in Ullmann's Encyclopedia of Industrial Chemistry, 2005, Wiley-VCH, Weinheim. Synthesis Several methods exist for the preparation of ''N''-methylaminophenol. It arises by decarboxylation of ''N''-4-hydroxyphenylglycine ( Glycin). It can be obtained by reaction of hydroquinone with methylamine. Application Metol is an excellent developing agent for most continuous tone developer applications, and it has been widely used in published developer formulas as well as commercial products. However, it is difficult to produce highly concentrated developer solutions using Metol, and therefore most Metol developers are supplied in dry chemical mix. A developer containing both Metol and hydroquinone is called an MQ developer. Th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hydroquinone
Hydroquinone, also known as benzene-1,4-diol or quinol, is an aromatic organic compound that is a type of phenol, a derivative of benzene, having the chemical formula C6H4(OH)2. It has two hydroxyl groups bonded to a benzene ring in a ''para'' position. It is a white granular solid. Substituted derivatives of this parent compound are also referred to as hydroquinones. The name "hydroquinone" was coined by Friedrich Wöhler in 1843. Production Hydroquinone is produced industrially in two main ways.Phillip M. Hudnall "Hydroquinone" in Ullmann's Encyclopedia of Industrial Chemistry 2002, Wiley-VCH, Weinheim. 2005 Wiley-VCH, Weinheim. . * The most widely used route is similar to the cumene process in reaction mechanism and involves the dialkylation of benzene with propene to give 1,4-diisopropylbenzene. This compound reacts with air to afford the bis(hydroperoxide), which is structurally similar to cumene hydroperoxide and rearranges in acid to give acetone and hydroquinone. * A se ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phenidone
Phenidone (1-phenyl-3-pyrazolidinone) is an organic compound that is primarily used 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.''Merck Index of Chemicals and Drugs, 9th ed.'' monograph 7115 Phenidone is Ilford's trademark for this material, which was first prepared in 1890. It was not until 1940 that J. D. Kendall, in the laboratories of Ilford Limited, discovered the reducing properties of this compound. Large scale production did not become feasible until 1951.Karlheinz Keller et al. "Photography" in ''Ullmann's Encyclopedia of Industrial Chemistry'', 2005, Wiley-VCH, Weinheim. Phenidone functions as a reducing agent. It converts to the ''N''-phenyl-hydroxypyrazole: Preparation Phenidone can be prepared by heating phenyl hydrazine Phenylhydrazine is the chemical compound with the formula . It is often abbreviated as . It is also ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Superadditive
In mathematics, a function f is superadditive if f(x+y) \geq f(x) + f(y) for all x and y in the domain of f. Similarly, a sequence \left\, n \geq 1, is called superadditive if it satisfies the inequality a_ \geq a_n + a_m for all m and n. The term "superadditive" is also applied to functions from a boolean algebra to the real numbers where P(X \lor Y) \geq P(X) + P(Y), such as lower probabilities. Properties If f is a superadditive function, and if 0 is in its domain, then f(0) \leq 0. To see this, take the inequality at the top: f(x) \leq f(x+y) - f(y). Hence f(0) \leq f(0+y) - f(y) = 0. The negative of a superadditive function is subadditive. Fekete's lemma The major reason for the use of superadditive sequences is the following lemma due to Michael Fekete. :Lemma: (Fekete) For every superadditive sequence \left\, n \geq 1, the limit \lim a_n/n is equal to \sup a_n/n. (The limit may be positive infinity, for instance, for the sequence a_n = \log n!.) For example, f( ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Development Mechanism
Development or developing may refer to: Arts *Development hell, when a project is stuck in development *Filmmaking, development phase, including finance and budgeting *Development (music), the process thematic material is reshaped *Photographic development * ''Development'' (album), a 2002 album by Nonpoint Business *Business development, a process of growing a business *Career development *Corporate development, a position in a business *Energy development, activities concentrated on obtaining energy from natural resources *Green development, a real estate concept that considers social and environmental impact of development *Land development, altering the landscape in any number of ways *Land development bank, a kind of bank in India *Leadership development *New product development *Organization development *Professional development *Real estate development *Research and development *Training and development *Fundraising, also called "development" Biology and medicine * Chil ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
P-aminophenol
4-Aminophenol (or ''para''-aminophenol or ''p''-aminophenol) is an organic compound with the formula H2NC6H4OH. Typically available as a white powder, it is commonly used as a developer for black-and-white film, marketed under the name Rodinal. Reflecting its slightly hydrophilic character, the white powder is moderately soluble in alcohols and can be recrystallized from hot water. In the presence of a base, it oxidizes readily. The methylated derivatives ''N''-methylaminophenol and ''N'',''N''-dimethylaminophenol are of commercial value. The compound is one of three isomeric aminophenols, the other two being 2-aminophenol and 3-aminophenol. __TOC__ Preparation From phenol It is produced from phenol by nitration followed by reduction with iron. Alternatively, the partial hydrogenation of nitrobenzene affords phenylhydroxylamine, which rearranges primarily to 4-aminophenol (Bamberger rearrangement). :C6H5NO2 + 2 H2 → C6H5NHOH + H2O :C6H5NHOH → HOC6H4NH2 From nitro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Glycin
Glycin, or N-(4-hydroxyphenyl)glycine, is N-substituted p-aminophenol. It is a photographic developing agent used in classic black-and-white developer solutions. It is unrelated to the amino acid glycine. It is typically characterized as thin plates of white or silvery powder, although aged samples appear brown. It is sparingly soluble in water and most organic solvents; it is readily soluble in alkalies and acids.{{cite encyclopedia, last1=Mitchell, first1=Stephen C., last2=Waring, first2=Rosemary H., encyclopedia=Ullmann's Encyclopedia of Industrial Chemistry, publisher=Wiley-VCH, year=2000, doi=10.1002/14356007.a02_099, isbn=978-3527306732, chapter=Aminophenols Glycin is structurally related to 4-aminophenol and Metol. Decarboxylation of glycin gives Metol. Glycin has a milder reduction potential than Metol. The two developers have markedly different character. Glycin is slower-acting, but much longer-lasting in solution. Glycin is rarely used as a developing agent, primarily ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ascorbic Acid
Vitamin C (also known as ascorbic acid and ascorbate) is a water-soluble vitamin found in citrus and other fruits and vegetables, also sold as a dietary supplement and as a topical 'serum' ingredient to treat melasma (dark pigment spots) and wrinkles on the face. It is used to prevent and treat scurvy. Vitamin C is an essential nutrient involved in the repair of tissue, the formation of collagen, and the enzymatic production of certain neurotransmitters. It is required for the functioning of several enzymes and is important for immune system function. It also functions as an antioxidant. Most animals are able to synthesize their own vitamin C. However, apes (including humans) and monkeys (but not all primates), most bats, some rodents, and certain other animals must acquire it from dietary sources. There is some evidence that regular use of supplements may reduce the duration of the common cold, but it does not appear to prevent infection. It is unclear whether supp ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Science Of Photography
The science of photography is the use of chemistry and physics in all aspects of photography. This applies to the camera, its lenses, physical operation of the camera, electronic camera internals, and the process of developing film in order to take and develop pictures properly. Optics Camera obscura The fundamental technology of most photography, whether digital or analog, is the camera obscura effect and its ability to transform of a three dimensional scene into a two dimensional image. At its most basic, a camera obscura consists of a darkened box, with a very small hole in one side, which projects an image from the outside world onto the opposite side. This form is often referred to as a pinhole camera. When aided by a lens, the hole in the camera doesn't have to be tiny to create a sharp and distinct image, and the exposure time can be decreased, which allows cameras to be handheld. Lenses A photographic lens is usually composed of several lens elements, which ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
