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The collodion process is an early photographic process. The collodion process, mostly synonymous with the "collodion wet plate process", requires the photographic material to be coated, sensitized, exposed, and developed within the span of about fifteen minutes, necessitating a portable darkroom for use in the field. Collodion is normally used in its wet form, but it can also be used in its dry form, at the cost of greatly increased exposure time. The increased exposure time made the dry form unsuitable for the usual portraiture work of most professional photographers of the 19th century. The use of the dry form was mostly confined to landscape photography and other special applications where minutes-long exposure times were tolerable.
Photographic paper is a paper coated with a light-sensitive chemical formula, like photographic film, used for making photographic prints. When photographic paper is exposed to light, it captures a latent image that is then developed to form a visible image; with most papers the image density from exposure can be sufficient to not require further development, aside from fixing and clearing, though latent exposure is also usually present. The light-sensitive layer of the paper is called the emulsion. The most common chemistry was based on silver halide but other alternatives have also been used.
Collodion is a flammable, syrupy solution of nitrocellulose in ether and alcohol. There are two basic types: flexible and non-flexible. The flexible type is often used as a surgical dressing or to hold dressings in place. When painted on the skin, collodion dries to form a flexible nitrocellulose film. While it is initially colorless, it discolors over time. Non-flexible collodion is often used in theatrical make-up. Collodion was also the basis of most wet-plate photography until it was superseded by modern gelatin emulsions.
The gelatin silver process is the most commonly used chemical process in black-and-white photography, and is the fundamental chemical process for modern analog color photography. As such, films and printing papers available for analog photography rarely rely on any other chemical process to record an image. A suspension of silver salts in gelatin is coated onto a support such as glass, flexible plastic or film, baryta paper, or resin-coated paper. These light-sensitive materials are stable under normal keeping conditions and are able to be exposed and processed even many years after their manufacture. The "dry plate" gelatin process was an improvement on the collodion wet-plate process dominant from the 1850s–1880s, which had to be exposed and developed immediately after coating.
Photogravure is a process for printing photographs, also sometimes used for reproductive intaglio printmaking. It is a photo-mechanical process whereby a copper plate is grained and then coated with a light-sensitive gelatin tissue which had been exposed to a film positive, and then etched, resulting in a high quality intaglio plate that can reproduce detailed continuous tones of a photograph.
The ambrotype, also known as a collodion positive in the UK, is a positive photograph on glass made by a variant of the wet plate collodion process. Like a print on paper, it is viewed by reflected light. Like the daguerreotype, which it replaced, and like the prints produced by a Polaroid camera, each is a unique original that could only be duplicated by using a camera to copy it.
A tintype, also known as a melanotype or ferrotype, is a photograph made by creating a direct positive on a thin sheet of metal, colloquially called 'tin', coated with a dark lacquer or enamel and used as the support for the photographic emulsion. It was introduced in 1853 by Adolphe Alexandre Martin in Paris, like the daguerreotype was fourteen years before by Daguerre. The daguerreotype was established and most popular by now, though the primary competition for the tintype would have been the ambrotype, that shared the same collodion process, but on a glass support instead of metal. Both found unequivocal, if not exclusive, acceptance in North America. Tintypes enjoyed their widest use during the 1860s and 1870s, but lesser use of the medium persisted into 1930s and it has been revived as a novelty and fine art form in the 21st century. It has been described as the first "truly democratic" medium for mass portraiture.
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.
The term alternative process refers to any non-traditional or non-commercial photographic printing process. Currently, the standard analog photographic printing process for black-and-white photographs is the gelatin silver process. Standard digital processes include the pigment print, and digital laser exposures on traditional color photographic paper.
Hand-colouring refers to any method of manually adding colour to a monochrome photograph, generally either to heighten the realism of the image or for artistic purposes. Hand-colouring is also known as hand painting or overpainting.
Gum printing is a way of making photographic reproductions without the use of silver halides. The process uses salts of dichromate in common with a number of other related processes such as sun printing.
The conservation and restoration of photographs is the study of the physical care and treatment of photographic materials. It covers both efforts undertaken by photograph conservators, librarians, archivists, and museum curators who manage photograph collections at a variety of cultural heritage institutions, as well as steps taken to preserve collections of personal and family photographs. It is an umbrella term that includes both preventative preservation activities such as environmental control and conservation techniques that involve treating individual items. Both preservation and conservation require an in-depth understanding of how photographs are made, and the causes and prevention of deterioration. Conservator-restorers use this knowledge to treat photographic materials, stabilizing them from further deterioration, and sometimes restoring them for aesthetic purposes.
Richard Leach Maddox was an English photographer and physician who invented lightweight gelatin negative dry plates for photography in 1871.
A chromogenic print, also known as a C-print or C-type print, a silver halide print, or a dye coupler print, is a photographic print made from a color negative, transparency or digital image, and developed using a chromogenic process. They are composed of three layers of gelatin, each containing an emulsion of silver halide, which is used as a light-sensitive material, and a different dye coupler of subtractive color which together, when developed, form a full-color image.
The following outline is provided as an overview of and topical guide to photography:
RA-4 is Kodak's proprietary name for the chemical process most commonly used to make color photographic prints. It is used for both minilab wet silver halide digital printers of the types most common today in photo labs and drug stores, and for prints made with older-type optical enlargers and manual processing.
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, paper, or fabric. The substrate is often flexible and known as a film base.
Dye transfer is a continuous-tone color photographic printing process. It was used to print Technicolor films, as well as to produce paper colour prints used in advertising, or large transparencies for display.
The oil print process is a photographic printmaking process that dates to the mid-19th century. Oil prints are made on paper on which a thick gelatin layer has been sensitized to light using dichromate salts. After the paper is exposed to light through a negative, the gelatin emulsion is treated in such a way that highly exposed areas take up an oil-based paint, forming the photographic image.
The conservation and restoration of photographic plates is caring for and maintaining photographic plates to preserve their materials and content. It covers the necessary measures that can be taken by conservators, curators, collection managers, and other professionals to conserve the material unique to photographic plate processes. This practice includes understanding the composition and agents of deterioration of photographic plates, as well as the preventive conservation and interventive conservation measures that can be taken to increase their longevity.
