A History of Photographic
Processes
From Wikipedia, by Sylvia Hasenkopf
Daguerreotype
A daguerreotype (original French: daguerréotype) is an early type of photograph, developed by Louis Daguerre, in which the image is exposed directly onto a mirror-polished surface of silver bearing a coating of silver halide particles deposited by iodine vapor. In later developments bromine and chlorine vapors were also used, resulting in shorter exposure times. The daguerreotype is a negative image, but the mirrored surface of the metal plate reflects the image and makes it appear positive in the proper light. Thus, daguerreotype is a direct photographic process without the capacity for duplication.
While the daguerreotype was not the first photographic process to be
invented, earlier processes required hours for successful exposure, which made
daguerreotype the first commercially viable photographic process and the first
to permanently record and fix an image with exposure time compatible with
portrait photography.
The daguerreotype is named after one of its inventors, French artist and chemist Louis J.M. Daguerre, who announced its perfection in 1839 after years of research and collaboration with Joseph Nicephore Niepce, applying and extending the 1724 discovery by Johann Heinrich Schultz that a silver and chalk mixture darkens when exposed to light. The French Academy of Sciences announced the daguerreotype process on January 9 of that year. The announcement of the daguerreotype process in 1839, along with William Fox Talbot's in the same year, marks the date used as the invention of photography.
Instead of Daguerre obtaining a French patent, the French government provided a pension for him. In Britain, Miles Berry, acting on Daguerre's behalf, obtained a patent for the daguerreotype process on August 14, 1839. Almost simultaneously, on August 19, 1839, the French government announced the invention as a gift "Free to the World."
The daguerreotype, along with the Tintype, is a photographic image allowing no direct transfer of the image onto another light-sensitive medium, as opposed to glass plate or paper negatives. Preparation of the plate prior to image exposure resulted in the formation of a layer of photo-sensitive silver halide, and exposure to a scene or image through a focusing lens formed a latent image. The latent image was made visible, or "developed", by placing the exposed plate over a slightly heated (about 90°F) cup of mercury.
The mercury vapour condensed on those places on the plate where the exposure light was most intense (highlights), and less so in darker areas of the image(shadows). This produced a picture in an amalgam, the mercury washing the silver out of the halides, solubilizing and amalgamating it into free silver particles which adhered to the exposed areas of the plate, leaving the unexposed silver halide ready to be removed by the fixing process. This resulted in the final unfixed image on the plate, which consisted of light and dark areas of grey amalgam on the plate. The developing box was constructed to allow inspection of the image through a yellow glass window to allow the photographer to determine when to stop development.
The next operation was to "fix" the photographic image permanently on the plate by dipping in a solution of hyposulphite of soda, often known as "fixer" or "hypo", to dissolve the unexposed halides. The image produced by this method is extremely fragile and susceptible to damage when handled improperly. Practically all daguerreotypes are protected from accidental damage by a glass-fronted case. It was discovered by experiment that treating the plate with heated gold chloride both tones and strengthens the image, although it remains quite delicate and requires a well-sealed case to protect against touch as well as oxidation of the fine silver deposits forming the blacks in the image. The best-preserved daguerreotypes dating from the nineteenth century are sealed in robust glass cases evacuated of air and filled with a chemically inert gas, typically nitrogen.
Calotype
Calotype or talbotype is an early photographic process introduced in 1841 by Henry Fox Talbot, using paper coated with silver iodide. The term calotype comes from the Greek κάλο for 'good', and τύπος for 'impression'.
The sensitive element of a calotype is silver iodide. With exposure to light, silver iodide decomposes to silver leaving iodine as free element. Excess silver iodide is washed away after oxidizing the pure silver with a second application of gallo-nitrate. As silver oxide is black, the resulting image is visible. Potassium bromide then is used to stabilize the silver oxide.
The salted paper's sensitive element is silver chloride formed when the salt (sodium chloride) reacts with silver nitrate. Silver chloride decomposes when in contact with light forming silver and chlorine evaporates. Excess silver chloride is washed out of the paper and the silver oxidizes in contact with gallo-nitrate. The silver oxide is stabilized on the paper with hypo.
Silver chloride makes better prints because it is less sensitive to temperature. During long exposures in sunlight the temperature on the paper can be considerable. (Taken from Alf B. Meier's publication Basic Photography with permission of the author)
Albumen Print
The albumen print, also called albumen silver print, was invented in 1850 by Louis Desire Blanquart-Evrard, and was the first commercially exploitable method of producing a photographic print on a paper base from a negative. It used the albumen found in egg whites to bind the photographic chemicals to the paper and became the dominant form of photographic positives from 1855 to the turn of the century, with a peak in the 1860-90 period. During the mid-1800s, the carte de visite became one of the more popular uses of the albumen method. In the 19th century, E. & H. T. Anthony & Comapny were the largest makers and distributors of the Albumen photographic prints and paper in the United States.
Because the image emerges as a direct result of exposure to light, without the aid of a developing solution, an albumen print may be said to be a printed rather than a developed photograph.
The table salt (sodium chloride) in the albumen emulsion forms silver chloride when in contact with silver nitrate. Silver chloride is unstable when exposed to light, which makes it decompose into silver and chlorine. The silver is oxidized into silver oxide during the development process and the remaining silver chloride is washed out during fixing. The black parts of the image are formed by silver oxide.
Ambrotype
The ambrotype process (from Greek ambrotos, "immortal") or amphitype is a photographic process that creates a positive photographic image on a sheet of glass using the wet collodion process. It was patented in 1854 by James Ambrose Cutting of Boston, in the United States. The wet plate collodion process was invented just a few years before that by Frederick Scott Archer, but Cutting used it as a positive, instead of a negative.
In Great Britain it was called collodion positive: one side of a very clean glass plate is covered with a thin layer of collodion, then dipped in a silver nitrate solution. The plate is exposed to the subject while still wet. (Exposure times vary from five to sixty seconds or more depending on the amount of available light.) The plate is then developed and fixed. The resulting negative, when viewed by reflected light against a black background, appears to be a positive image: the clear areas look black, and the exposed, opaque areas appear light. This effect is achieved by coating one side of the glass negative with black varnish. Either the emulsion side or the blank side can be covered with the varnish: when the blank side is blackened, the thickness of the glass adds a sense of depth to the image. In either case, another plate of glass is put over the fragile emulsion side to protect it, and the whole is mounted in a metal frame and kept in a protective case. In some instances the protective glass was cemented directly to the emulsion, generally with a balsam resin. This protected the image well but tended to make it darker.
The ambrotype was much less expensive to produce than the daguerreotype, and it lacked the daguerreotype's shiny metallic surface, which some found unappealing. By the late 1850s, the ambrotype was overtaking the daguerreotype in popularity; by the mid-1860s, the ambrotype itself was supplanted by the tintype and other processes.
Ambrotypes were often hand-tinted. Untinted ambrotypes are grayish-white and have less contrast and brilliance than daguerreotypes.
Ferrotype (Tintype)
Tintype, also melainotype and ferrotype, is a photograph made by creating a direct positive on a sheet of metal, usually iron or steel that is blackened by painting, laquering or enamelling and is used as a support for a collodion photographic emulsion.
Photographers usually worked outside at fairs, carnivals etc. and as the support of the tintype (there is no actual tin used) is resilient and does not need drying, instant photographs can be produced only a few minutes after taking the photograph.
An ambrotype uses the same process and methods on a sheet of glass that is mounted in a case with a black backing so the underexposed negative image appears as a positive. Tintypes did not need mounting in a case and were not as delicate as photographs that used glass for the support.
The process was identical to the wet plate process, where collodion is employed to produce a photographic emulsion where silver halide crystals ( silver bromide, silver chloride and silver iodide) are suspended in the collodion, and are chemically reduced to crystals of metallic silver that vary in density according to the original light values of the original image.
When a photographic negative image on film or plate is very underexposed, it appears as a positive when viewed against a dark background. This is the basis of the process: a very underexposed image is produced on a collodion photographic emulsion on a dark metal backing; thus viewed the image appears as a positive. The fact that an underexposed image is required means that the effective film speed is increased and shorter exposures can be used, which is a great advantage in portraiture.
The process was first described by Adolphe-Alexandre Martin in France in 1853, and patented in the United States on February 19, 1856 by Hamilton Smith, professor at Kenyon College, in Ohio. William Kloen also patented the process in the United Kingdom in the same year. It was first called melainotype, and then ferrotype (by a rival manufacturer of the iron plates used); finally came the name tintype. All three names describe both the process and the resulting photograph.
While the ambrotype remained very popular in the rest of the world, the tintype process had superseded the ambrotype in the United States by the end of the Civil War. It became the most common photographic process until the introduction of modern, gelatin-based processes and the invention of the reloadable amateur camera by the Kodak company. Ferrotypes had waned in popularity by the end of the 19th century, although a few makers were still around as late as the 1950s and the images are still made as novelties at some European carnivals.
The tintype was a minor improvement to the ambrotype, replacing the glass plate of the original process with a thin piece of black-enameled, or japanned, iron (hence ferro). The new materials reduced costs considerably; and the image, in gelatin-silver emulsion on the varnished surface, has proven to be very durable. Like that of the ambrotype, the tintype's image is technically negative; but, because of the black background, it appears as a positive. Since the tintype 'film' was the same as the final print, most tintype images appear reversed (left to right) from reality. Some cameras were fitted with mirrors or a 45-degree prism to reverse (and thus correct) the image, while some photographers would photograph the reversed tintype to produce a properly oriented image.
Tintypes are simple and fast to prepare, compared to other early photographic techniques. A photographer could prepare, expose, develop, and varnish a tintype plate in a few minutes, quickly having it ready for a customer. Earlier tintypes were often cased, as were daguerreotypes and ambrotypes; but uncased images in paper sleeves and for albums were popular from the beginning.
Dry Plate
Dry plate, also known as gelatine process, is the first economically successful durable photographic medium. It was invented by Dr. Richard L. Maddox in 1871, and by 1879 it was so well introduced that the first dry plate factory had been established.
The wet plate was, without question, a successful photographic process, but it had its drawbacks. Primarily there was the fact that a wet plate had to be used within twenty minutes of preparing and secondly because of its slow photographic speed. The preparation of wet plates required numerous chemicals, beakers and liquids; all mixed in the dark in a portable tent if the photographer was planning on photographing away from the studio.
From the beginning of the wet plate process there were attempts to make plates durable, most notable are the attempts by Robert Bingham in 1850 and Richard H. Norris 1856. Both these processes lacked economical success, though Norris was slightly more successful, even establishing a factory.
The next notable attempt to make durable plates was by Joseph Sidebotham who used a collodion albumen mixture in 1861.
The lack of success for the above was not that it did not work, or that it was complicated but because at the time transportation, especially timely transportation, was complicated; by the time a plate from Birmingham in England reached New York in the USA it could be best used as window pane.
In addition America had an import tariff in place to protect the national glass making industry. The American Excise Department did not recognise the photographic plates and taxed them strictly as sheets of glass. Locally these plates had a limited success though.
Gelatin emulsions as proposed by Maddox were very sensitive to touch and mechanical friction and not much more sensitive than collodion emulsions to light.
Charles Bennett discovered a method of hardening the emulsion, making it more resistant to friction in 1873. In 1878, Bennett discovered that by prolonged heating, the sensitivity of the emulsion could be greatly increased.
George Eastman developed a machine to coat plates, reducing the cost of photography in 1879. A competitor of Eastman in the development and manufacture of Gelatin dry plates was the architectural photographer Albert Levy.