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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] |
Platinotype
Platinum prints, also called ''platinotypes'', are photographic prints made by a monochrome printing process involving platinum. Platinum tones range from warm black, to reddish brown, to expanded mid-tone grays that are unobtainable in silver prints. Unlike the silver print process, platinum lies on the paper surface, while silver lies in a gelatin or albumen emulsion that coats the paper. As a result, since no gelatin emulsion is used, the final platinum image is absolutely matte with a deposit of platinum (and/or palladium, its sister element which is also used in most platinum photographs) absorbed slightly into the paper. Platinum prints are the most durable of all photographic processes. The platinum group metals are very stable against chemical reactions that might degrade the print—even more stable than gold. It is estimated that a platinum image, properly made, can last thousands of years. Some of the desirable characteristics of a platinum print include: * The re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wayback Machine
The Wayback Machine is a digital archive of the World Wide Web founded by the Internet Archive, a nonprofit based in San Francisco, California. Created in 1996 and launched to the public in 2001, it allows the user to go "back in time" and see how websites looked in the past. Its founders, Brewster Kahle and Bruce Gilliat, developed the Wayback Machine to provide "universal access to all knowledge" by preserving archived copies of defunct web pages. Launched on May 10, 1996, the Wayback Machine had more than 38.2 million records at the end of 2009. , the Wayback Machine had saved more than 760 billion web pages. More than 350 million web pages are added daily. History The Wayback Machine began archiving cached web pages in 1996. One of the earliest known pages was saved on May 10, 1996, at 2:08p.m. Internet Archive founders Brewster Kahle and Bruce Gilliat launched the Wayback Machine in San Francisco, California, in October 2001, primarily to address the problem of web co ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sodium Metabisulfite
Sodium metabisulfite or sodium pyrosulfite (IUPAC spelling; Br. E. sodium metabisulphite or sodium pyrosulphite) is an inorganic compound of chemical formula Na2S2O5. The substance is sometimes referred to as disodium metabisulfite. It is used as a disinfectant, antioxidant, and preservative agent. Preparation Sodium metabisulfite can be prepared by treating a solution of sodium hydroxide with sulfur dioxide. When conducted in warm water, Na2SO3 initially precipitates as a yellow solid. With more SO2, the solid dissolves to give the disulfite, which crystallises upon cooling. :SO2 + 2 NaOH → Na2SO3 + H2O :SO2 + Na2SO3 → Na2S2O5 which yields a residue of colourless solid Na2S2O5. Chemical structure The anion metabisulfite consists of an SO2 group linked to an SO3 group, with the negative charge more localised on the SO3 end. The S–S bond length is 2.22 Å, and the "thionate" and "thionite" S–O distances are 1.46 and 1.50 Å, respectively. Reactivity Upon d ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Black Light
A blacklight, also called a UV-A light, Wood's lamp, or ultraviolet light, is a lamp that emits long-wave (UV-A) ultraviolet light and very little visible light. One type of lamp has a violet filter material, either on the bulb or in a separate glass filter in the lamp housing, which blocks most visible light and allows through UV, so the lamp has a dim violet glow when operating. Blacklight lamps which have this filter have a lighting industry designation that includes the letters "BLB". This stands for "blacklight blue". A second type of lamp produces ultraviolet but does not have the filter material, so it produces more visible light and has a blue color when operating. These tubes are made for use in "bug zapper" insect traps, and are identified by the industry designation "BL". This stands for "blacklight". Blacklight sources may be specially designed fluorescent lamps, mercury-vapor lamps, light-emitting diodes (LEDs), lasers, or incandescent lamps. In medicine, f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mercury Vapor Lamp
A mercury-vapor lamp is a gas-discharge lamp that uses an electric arc through vaporized mercury to produce light. The arc discharge is generally confined to a small fused quartz arc tube mounted within a larger soda lime or borosilicate glass bulb. The outer bulb may be clear or coated with a phosphor; in either case, the outer bulb provides thermal insulation, protection from the ultraviolet radiation the light produces, and a convenient mounting for the fused quartz arc tube. Mercury vapor lamps are more energy efficient than incandescent lamps with luminous efficacies of 35 to 55 lumens/watt. Their other advantages are a long bulb lifetime in the range of 24,000 hours and a high intensity, clear white light output. For these reasons, they are used for large area overhead lighting, such as in factories, warehouses, and sports arenas as well as for streetlights. Clear mercury lamps produce a greenish light due to mercury's combination of spectral lines. This is not flatt ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ultraviolet
Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nanometer, nm (with a corresponding frequency around 30 Hertz, PHz) to 400 nm (750 Hertz, THz), shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight, and constitutes about 10% of the total electromagnetic radiation output from the Sun. It is also produced by electric arcs and specialized lights, such as mercury-vapor lamps, tanning lamps, and black lights. Although long-wavelength ultraviolet is not considered an ionizing radiation because its photons lack the energy to ionization, ionize atoms, it can cause chemical reactions and causes many substances to glow or fluorescence, fluoresce. Consequently, the chemical and biological effects of UV are greater than simple heating effects, and many practical applications of UV radiation derive from its interactions with organic molecules. Short-wave ultraviolet light damages DNA and sterilizes surf ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Contact Print
A contact print is a photographic image produced from film; sometimes from a film negative, and sometimes from a film positive or paper negative. In a darkroom an exposed and developed piece of film or photographic paper is placed emulsion side down, in contact with a piece of photographic paper, light is briefly shone through the negative or paper and then the paper is developed to reveal the final print. The defining characteristic of a contact print is that the resulting print is the same size as the original, rather than having been projected through an enlarger. Basic tools Contact printing is a simple and inexpensive process. Its simplicity avails itself to those who may want to try darkroom processing without buying an enlarger. One or more negatives are placed on a sheet of photographic paper which is briefly exposed to a light source. The light may come from a low wattage frosted bulb hanging above an easel which holds them together, or contained in an exposure ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Enlarger
An enlarger is a specialized transparency projector used to produce photographic prints from film or glass negatives, or from transparencies. Construction All enlargers consist of a light source, normally an incandescent light bulb shining though a condenser or translucent screen to provide even illumination, a holder for the negative or transparency, and a specialized lens for projection. The light passes through a film holder, which holds the exposed and developed photographic negative or transparency. Prints made with an enlarger are called ''enlargements''. Typically, enlargers are used in a darkroom, an enclosed space from which extraneous light may be excluded; some commercial enlargers have an integral dark box so that they can be used in a light-filled room. History Josef Maria Eder, in his ''History of Photography'' attributes the invention of photographic enlargement to Humphry Davy who realised the idea of using a solar microscope to project images onto sensitis ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Photographic Negative
In photography, a negative is an image, usually on a strip or sheet of transparent plastic film, in which the lightest areas of the photographed subject appear darkest and the darkest areas appear lightest. This reversed order occurs because the extremely light-sensitive chemicals a camera film must use to capture an image quickly enough for ordinary picture-taking are darkened, rather than bleached, by exposure to light and subsequent photographic processing. In the case of color negatives, the colors are also reversed into their respective complementary colors. Typical color negatives have an overall dull orange tint due to an automatic color-masking feature that ultimately results in improved color reproduction. Negatives are normally used to make positive prints on photographic paper by projecting the negative onto the paper with a photographic enlarger or making a contact print. The paper is also darkened in proportion to its exposure to light, so a second reversal result ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Duotone
Duotone (sometimes also known as ''Duplex'') is a halftone reproduction of an image using the superimposition of one contrasting color halftone over another color halftone. This is most often used to bring out middle tones and highlights of an image. Traditionally the superimposed contrasting halftone color is black and the most commonly implemented colors are blue, yellow, brown, and red, however there are many varieties of color combinations used. Modern use Due to recent advances in technology, duotones, tritones, and quadtones can be easily created using image manipulation programs. Duotone color mode in Adobe Photoshop computes the highlights and middle tones of a monochrome (grayscale or black-and-white) image in one color, and allows the user to choose any color as the second color. Duograph A fake duotone, or duograph, is done by printing a single color with a one-color halftone over it. This process is generally not preferred over a regular duotone, as it loses much of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
CMYK
The CMYK color model (also known as process color, or four color) is a subtractive color model, based on the CMY color model, used in color printing, and is also used to describe the printing process itself. The abbreviation ''CMYK'' refers to the four ink plates used: cyan, magenta, yellow, and key (black). The CMYK model works by partially or entirely masking colors on a lighter, usually white, background. The ink reduces the light that would otherwise be reflected. Such a model is called ''subtractive'' because inks "subtract" the colors red, green and blue from white light. White light minus red leaves cyan, white light minus green leaves magenta, and white light minus blue leaves yellow. In additive color models, such as RGB, white is the "additive" combination of all primary colored lights, black is the absence of light. In the CMYK model, it is the opposite: white is the natural color of the paper or other background, black results from a full combination of colo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
