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Photoemulsion
Photographic emulsion is a light-sensitive colloid used in film-based photography. Most commonly, in silver-gelatin photography, it consists of silver halide crystals dispersed in gelatin. The emulsion is usually coated onto a substrate of glass, films (of cellulose nitrate, cellulose acetate or polyester), paper, or fabric. Photographic emulsion is not a true emulsion, but a suspension of solid particles (silver halide) in a fluid (gelatin in solution). However, the word ''emulsion'' is customarily used in a photographic context. Gelatin or gum arabic layers sensitized with dichromate used in the dichromated colloid processes carbon and gum bichromate are sometimes called ''emulsions''. Some processes do not have emulsions, such as platinum, cyanotype, salted paper, or kallitype. Components Photographic emulsion is a fine suspension of insoluble light-sensitive crystals in a colloid sol, usually consisting of gelatin. The light-sensitive component is one or a mixture o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Light
Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 terahertz, between the infrared (with longer wavelengths) and the ultraviolet (with shorter wavelengths). In physics, the term "light" may refer more broadly to electromagnetic radiation of any wavelength, whether visible or not. In this sense, gamma rays, X-rays, microwaves and radio waves are also light. The primary properties of light are intensity, propagation direction, frequency or wavelength spectrum and polarization. Its speed in a vacuum, 299 792 458 metres a second (m/s), is one of the fundamental constants of nature. Like all types of electromagnetic radiation, visible light propagates by massless elementary particles called photons that represents the quanta of electromagnetic field, and can be analyzed as both waves and par ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gum Bichromate
Gum bichromate is a 19th-century photographic printing process based on the light sensitivity of dichromates. It is capable of rendering painterly images from photographic negatives. Gum printing is traditionally a multi-layered printing process, but satisfactory results may be obtained from a single pass. Any color can be used for gum printing, so natural-color photographs are also possible by using this technique in layers. History and process overview Gum bichromate, or gum dichromate as it is also known, is a photographic printing process invented in the early days of photography when, in 1839, Mungo Ponton discovered that dichromates are light sensitive. William Henry Fox Talbot later found that sensitized dichromated colloids such as gelatin and gum arabic became insoluble in water after exposure to sunlight. Alphonse Poitevin added carbon pigment to the colloids in 1855, creating the first carbon print. In 1858, John Pouncy used colored pigment with gum arabic to creat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Biocide
A biocide is defined in the European legislation as a chemical substance or microorganism intended to destroy, deter, render harmless, or exert a controlling effect on any harmful organism. The US Environmental Protection Agency (EPA) uses a slightly different definition for biocides as "a diverse group of poisonous substances including preservatives, insecticides, disinfectants, and pesticides used for the control of organisms that are harmful to human or animal health or that cause damage to natural or manufactured products". When compared, the two definitions roughly imply the same, although the US EPA definition includes plant protection products and some veterinary medicines. The terms "biocides" and "pesticides" are regularly interchanged, and often confused with "plant protection products". To clarify this, pesticides include both biocides and plant protection products, where the former refers to substances for non-food and feed purposes and the latter refers to substances ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Surfactant
Surfactants are chemical compounds that decrease the surface tension between two liquids, between a gas and a liquid, or interfacial tension between a liquid and a solid. Surfactants may act as detergents, wetting agents, emulsifiers, foaming agents, or dispersants. The word "surfactant" is a blend of ''surface-active agent'', coined . Agents that increase surface tension are "surface active" in the literal sense but are not called surfactants as their effect is opposite to the common meaning. A common example of surface tension increase is salting out: by adding an inorganic salt to an aqueous solution of a weakly polar substance, the substance will precipitate. The substance may itself be a surfactant – this is one of the reasons why many surfactants are ineffective in sea water. Composition and structure Surfactants are usually organic compounds that are amphiphilic, meaning each molecule contains both a hydrophilic "water-seeking" group (the ''head''), and a hydro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Buffer Solution
A buffer solution (more precisely, pH buffer or hydrogen ion buffer) is an aqueous solution consisting of a mixture of a weak acid and its conjugate base, or vice versa. Its pH changes very little when a small amount of strong acid or base is added to it. Buffer solutions are used as a means of keeping pH at a nearly constant value in a wide variety of chemical applications. In nature, there are many living systems that use buffering for pH regulation. For example, the bicarbonate buffering system is used to regulate the pH of blood, and bicarbonate also acts as a buffer in the ocean. Principles of buffering Buffer solutions resist pH change because of a chemical equilibrium between the weak acid HA and its conjugate base A−: When some strong acid is added to an equilibrium mixture of the weak acid and its conjugate base, hydrogen ions (H+) are added, and the equilibrium is shifted to the left, in accordance with Le Chatelier's principle. Because of this, the hydrogen io ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Silver Nitrate
Silver nitrate is an inorganic compound with chemical formula . It is a versatile precursor to many other silver compounds, such as those used in photography. It is far less sensitive to light than the halides. It was once called ''lunar caustic'' because silver was called ''luna'' by ancient alchemists who associated silver with the moon. In solid silver nitrate, the silver ions are three- coordinated in a trigonal planar arrangement. Synthesis and structure Albertus Magnus, in the 13th century, documented the ability of nitric acid to separate gold and silver by dissolving the silver. Indeed silver nitrate can be prepared by dissolving silver in nitric acid followed by evaporation of the solution. The stoichiometry of the reaction depends upon the concentration of nitric acid used. :3 Ag + 4 HNO3 (cold and diluted) → 3 AgNO3 + 2 H2O + NO :Ag + 2 HNO3 (hot and concentrated) → AgNO3 + H2O + NO2 The structure of silver nitrate has been examined by X-ray crystallography sever ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Black-and-white
Black-and-white (B&W or B/W) images combine black and white in a continuous spectrum, producing a range of shades of grey. Media The history of various visual media began with black and white, and as technology improved, altered to color. However, there are exceptions to this rule, including black-and-white fine art photography, as well as many film motion pictures and art film(s). Photography Contemporary use Since the late 1960s, few mainstream films have been shot in black-and-white. The reasons are frequently commercial, as it is difficult to sell a film for television broadcasting if the film is not in color. 1961 was the last year in which the majority of Hollywood films were released in black and white. Computing In computing terminology, ''black-and-white'' is sometimes used to refer to a binary image consisting solely of pure black pixels and pure white ones; what would normally be called a black-and-white image, that is, an image containing shades of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Panchromatic
Panchromatic emulsion is a type of black-and-white photographic emulsion that is sensitive to all wavelengths of visible light. Description A panchromatic emulsion renders a realistic reproduction of a scene as it appears to the human eye, although with no colors. Almost all modern photographic film is panchromatic. Some older types of film were orthochromatic and were not sensitive to certain wavelengths of light. As naturally prepared, a silver halide photographic emulsion is much more sensitive to blue and UV light than to green and red wavelengths. The German chemist Hermann W. Vogel found out how to extend the sensitivity into the green, and later the orange, by adding sensitising dyes to the emulsion. By the addition of erythrosine the emulsion could be made orthochromatic while some cyanine derivatives confer sensitivity to the whole visible spectrum making it panchromatic. However, his technique was not extended to achieve a fully panchromatic film until the early 190 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Subtractive Color
Subtractive color or subtractive color mixing predicts the spectral power distribution of light after it passes through successive layers of partially absorbing media. This idealized model is the essential principle of how dyes and inks are used in color printing and photography where the perception of color is elicited after white light passes through microscopic "stacks" of partially absorbing media allowing some wavelengths of light to reach the eye and not others. Process The subtractive color mixing model predicts the resultant spectral power distribution of light filtered through overlaid partially absorbing materials on a reflecting or transparent surface. Each layer partially absorbs some wavelengths of light from the illumination spectrum while letting others pass through, resulting in a colored appearance. The resultant spectral power distribution is predicted by sequentially taking the product of the spectral power distributions of the incoming light and transmissiv ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dye Couplers
Dye coupler is present in chromogenic film and paper used in photography, primarily color photography. When a color developer reduces ionized (exposed) silver halide crystals, the developer is oxidized, and the oxidized molecules react with dye coupler molecules to form a dye ''in situ.'' The silver image is removed by subsequent bleach and fix processes, so the final image will consist of the dye image. Dye coupler technology has seen considerable advancement since the beginning of modern color photography. Major film and paper manufacturers have continually improved the stability of the image dye by improving couplers, particularly since the 1980s, so that archival properties of images are enhanced in newer color papers and films. Generally speaking, dye couplers for paper use are given more emphasis on the image permanence than those for film use, but some modern films (such as Fujichrome Provia Provia is a brandname for a pair of daylight-balanced color reversal films ( ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Photosensitizer
Photosensitizers produce a physicochemical change in a neighboring molecule by either donating an electron to the substrate or by abstracting a hydrogen atom from the substrate. At the end of this process, the photosensitizer eventually returns to its ground state, where it remains chemically intact until the photosensitizer absorbs more light. This means that the photosensitizer remains unchanged before and after the energetic exchange, much like heterogeneous photocatalysis. One branch of chemistry which frequently utilizes photosensitizers is polymer chemistry, using photosensitizers in reactions such as photopolymerization, photocrosslinking, and photodegradation. Photosensitizers are also used to generate prolonged excited electronic states in organic molecules with uses in photocatalysis, photon upconversion and photodynamic therapy. Generally, photosensitizers absorb electromagnetic radiation consisting of infrared radiation, visible light radiation, and ultraviolet radiati ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Visible Spectrum
The visible spectrum is the portion of the electromagnetic spectrum that is visual perception, visible to the human eye. Electromagnetic radiation in this range of wavelengths is called ''visible light'' or simply light. A typical human eye will respond to wavelengths from about 380 to about 750 nanometers. In terms of frequency, this corresponds to a band in the vicinity of 400–790 Terahertz (unit), terahertz. These boundaries are not sharply defined and may vary per individual. Under optimal conditions these limits of human perception can extend to 310 nm (ultraviolet) and 1100 nm (near infrared). The optical spectrum is sometimes considered to be the same as the visible spectrum, but some authors define the term more broadly, to include the ultraviolet and infrared parts of the electromagnetic spectrum as well. The spectrum does not contain all the colors that the human visual system can distinguish. ''Excitation purity, Unsaturated colors'' such as pink, or ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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