The process of silver gelatin is the photographic process used with currently available black-and-white films and black paper. Suspension of silver salt in gelatin is coated onto a support such as glass, plastic or flexible film, baryta paper, or resin coated paper. These light-sensitive materials are stable under normal storage conditions and can be exposed and processed even years after manufacture. This is in contrast to the dominant wet-plate collodion process of the 1850s 1880s, which must be exposed and developed immediately after coating.
Video Gelatin silver process
Histori
The process of silver gelatin was introduced by Richard Leach Maddox in 1871 with subsequent substantial increases in sensitivity obtained by Charles Harper Bennett in 1878.
The Gelatin silver printing paper was made in early 1874 on a commercial basis, but the quality was poor because the dry-plate emulsion was coated with paper only as an afterthought. Coating machines for the production of sensitive paper rolls were continuously used in the mid-1880s, although the use of silver gelatin printing material was not widely available until the 1890s. The earliest papers had no baryta layers, and it was not until the 1890s that the baryta layers became a commercial operation, first in Germany, in 1894, and then taken by Kodak in 1900.
Although the baryta coating plays an important part in making fine and glossy prints, baryta paper in 1890 did not produce the shiny or glossy print surface that became the standard for art photography in the twentieth century. Woven agents, textured paper, and a thin layer of baryta that are not too dense produce a shiny and textured appearance. Higher gloss paper first became popular in the 1920s and 30s when photography shifted from pictorialism to modernism, photojournalism, and "straight" photography.
Research over the past 125 years has led to current materials that exhibit low granules and high sensitivity to light.
Timeline
- 1874 - The first commercial production of gelatin developed paper (DOP)
- 1885 - Coating machine was first used in the manufacture of gelatin DOP for continuous rolling
- 1894 - Baryta coating added to commercial DOP gelatin production
- 1920s - Increased popularity of glossy and semi-gloss paper
- 1960 - Black and white eclipse color photography for the first time
Maps Gelatin silver process
Technology
Overview
Gelatin silver print or gelatin developing paper (DOP) is a monochrome imaging process based on the silver halide light sensitivity. They have been made for contact printing and the purpose of zooming by modifying the light sensitivity of the paper. A short to negative exposure produces a latent image, which is then made visible to the developing agent. The image is then made permanent by the treatment in a photographic fixer, which removes the remaining light-sensitive silver halide. And finally, the water bath cleaned the fixer from the mold. The final image consists of small silver particles bonded in a layer of gelatin. This gelatin image layer is only one of four layers found in typical silver gelatin printing, which usually includes coat layers, image layers, baryta, and paper.
Layer structure
A gelatine silver mold consists of four layers: the base of paper, baryta, gelatin binder, and protective gelatin layer or coat. The multi-layer structure of silver gelatin molds and silver salt imaging sensitivity requires special coating equipment and meticulous manufacturing techniques to produce consistent products that are free from dirt harmful to the image.
The paper or support base serves as the substrate to which the next layer is attached. Paper is in many ways ideal support: light, flexible, and powerful enough to withstand the wet and regular handling process. The base of photographic paper should be free of photoactive impurities such as iron and lignin. To obtain this purity, this paper was originally made of cotton, although after World War I there was a transition to pure wood pulp, which has been in use since then.
The second layer is baryta, a white opaque layer made primarily of gelatin and barium sulfate. The goal is to cover the paper fibers and form a smooth surface to coat the gelatin. Surface textures are made by various textures of felts used in paper drying, calendaring, and embossing before or after application of the baryta coating depending on the desired effect.
The third layer is a bonding gelatin that holds silver granules from photographic images. Gelatin has many qualities that make it an ideal photography binder. Among these are toughness and abrasion resistance when dry and its ability to swell and allow penetration of processing solutions. The fourth layer, called overcoat, supercoat, or topcoat, is a very thin layer of gelatin applied over the gelatin binder. It acts as a protective layer, providing superior abrasion resistance to the print surface.
Images and processing
Before the paper is exposed, the image layer is a gelatin matrix that clearly holds a light-sensitive silver halide. For silver gelatin molds, silver halides are usually a combination of silver bromide and silver chloride. Negative exposure is usually done with magnifying, though contact printing is also popular, especially among amateurs in the early twentieth century and among large-format camera users. Wherever light grabs the paper, silver halides form tiny spots of silver metal on its surface. Light causes the reduction of silver salts into silver metal. This exposure is the largest in the printed area corresponding to the obvious parts of the negative, being a shadow or area with high density of the mold.
This process is the formation of a latent image, because it forms an invisible image on paper which is then made visible by the development. So the paper is now placed in the developer, which converts the silver halide particles that have the image of a latent spot on them into a silver metal. Now the image is visible, but the remaining unopened silver halides still have to be removed to make the image permanent. But first the mold is placed into a soak tub, which stops the construction and prevents the developer contaminating the next bathhouse: fixer.
The fixer, usually sodium thiosulfate, is capable of removing unexpanded silver halides by forming a water-soluble complex with it. And finally, washing water is sometimes preceded by a washing aid removing the fixer from the mold, leaving a picture consisting of silver particles stored in a clear layer of gelatine image. Toning is sometimes used for permanent or aesthetic purposes and following installation steps. Selenium, gold, and sulfur toner are the most common and act well by altering some of the silver to other compounds (such as silver selenide or silver sulphide) or partially replacing silver with other metals (such as gold).
When small crystals (called grains ) of silver salts such as silver bromide and silver chloride are exposed to light, some free silver metal atoms are released. These free silver atoms form latent images . This latent image is relatively stable and will last for several months without degradation as long as the film remains dark and cold. Movies developed use solutions that reduce silver halides in the presence of atom-free silver. An 'amplification' of the latent image occurs as the silver halide near the silver atom is freely reduced to a silver metal. The power, temperature, and time allowing the developer to act allow the photographer to control the contrast of the final image. This development then stops by neutralizing the developer in the second bath.
After development is complete, undeveloped silver salts should be removed by fixing in sodium thiosulfate or ammonium thiosulfate, and then negative or the print should be washed in clean water. The final image consists of a silver metal embedded in the layer of gelatin.
All silver gelatin photography materials are subject to damage. The silver particles that make up the image are susceptible to oxidation, leading to yellowing and fading of the image. Poor processing can also produce various forms of image degradation, due to the rest of the silver-thiosulfate complex. Toning improves the silver image stability by coating a silver image with a metal that is less easily oxidized like gold, or by converting part of the silver image particles into more stable compounds, such as silver selenide or silver sulphide.
Print digital silver gelatin
Also known as digital bromides, silver black and white gelatin prints imaged through digital output devices such as Durst Lambda and OcÃÆ' © LightJet, have been developed for the art market by Ilford Imaging - now Harman Technology is working with Steve McLeod.
By adapting large-format paper processors in conjunction with manufacturers, McLeod's innovation leads the way to the possibility of producing black and white coated (RC) and fiber (FB) prints.
Ilford, in collaboration with Metro Imaging, London adapted their FB Galerie emulsion paper and light sensitivity so that it would receive the full spectrum of RGB laser channels.
In molecular biology
The basically the same procedure called "silver staining" is used in molecular biology to visualize DNA or protein after gel electrophoresis, usually SDS-PAGE. The latent image is formed by DNA molecules or proteins (ie, reduced silver that selectively precipitates on the molecules). Known for being almost as sensitive as autoradiography, the "gold standard" technique, but not widely used because of the use of radioactive material.
References
Further reading
- Adams, Ansel (1950). Print: Print and enlarge contacts (2 ed.). Boston: New York Graphic Society. ISBN: 0821207180.
- Eaton, G. T. (1965). Photographic chemistry in black and white photography and color. Hastings-on-Hudson, N.Y.,: Morgan & amp; Morgan.
- Gray, G. G. (1987). From Papyrus to RC Paper: History of Paper Support. Pioneers of Photography: Their Achievements in Science and Technology. E. Ostroff. Springfield, VA,: The Society for Imaging Science and Technology: 37-46.
- Jacobson, Ralph E. (2000). Photography guides: photography and digital imaging (9th ed.). Boston, Mass.: Focal Press. ISBN: 0240515749.
- Rogers, David (2007). Photographic chemistry: from classical to digital technology . Cambridge: RSC Publ. ISBNÃ, 0-85404-273-3.
- Weaver, G. (2008) A Guide to Fiber-Base Gelatin Silver Print Conditions and Deterioration. George Eastman House, International Museum of Photography and Film.
- Wentzel, F. and L. W. Sipley (1960). Memoirs of a photochemist. Philadelphia: Museum of American Photography.
External links
- Notes about Photos @ George Eastman House
- Atlas Graph @ Permanent Institution Image
- Mark Scholer Pedersen. "The silver gelatin dry plate process". photography.com alternative . Retrieved 2017-08-30 .
Source of the article : Wikipedia
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