Physical photographs usually consist of three components: the final image material (e.g. silver, platinum, dyes, or pigments), the transparent binder layer (e.g. albumen, collodion, or gelatin) in which the final image material is suspended, and the primary support (e.g. paper, glass, metal, or plastic). These components affect the susceptibility of photos to damage and the preservation and conservation methods required. Photograph preservation and conservation are also concerned with the
negatives from which most old
photographic prints are made. Most negatives are either glass plate or film-based.
Timeline Source:
1816: HeliographyThe first person who succeeded in producing a paper negative of the camera image was
Joseph Nicephore Niepce. He coated pewter plates with
bitumen (an asphaltic varnish that hardens with exposure to light) and put them in a
camera obscura. After exposure to sunlight for a long time, the parts that were exposed to light became hard and the parts that were not could be washed off with
lavender oil.
1837: DaguerreotypeThe daguerreotype process (named after
Louis Jacques Mande Daguerre) produces a unique image, as there is no negative created. After coating a copper plate with light-sensitive silver iodide, the plate is exposed to an image for over 20 minutes and then treated with fumes from heated mercury. The longer the exposure to light, the more mercury fumes are adsorbed by the silver iodide. After the plate is washed with salt water, the image appears, reversed. This was the earliest photographic process to gain popularity in America. It was used until around 1860.
1839: Salt printThis was the dominant form of paper print until Albumen prints were introduced in 1850. Salt prints were made using both paper and glass negatives.
1841: CalotypeWilliam Henry Fox Talbot invented the negative-positive system of photography commonly used today. He first developed the Talbotype, which used silver chloride to sensitize paper. After improving the process by using silver iodide, he renamed it Calotype. The process could produce many positive images, but they were not as sharp because they were printed on fibrous paper rather than glass.
1842: Cyanotype (Ferro-plusiate, Blue process)This process forms blue-colored images through a reaction to iron salts.
John Herschel studied it in order to reproduce his complicated math formulas and memos. Other processes that fall into this category include Kallitype, Vandyketype, and Platinum printing.
1850: Albumen printThis process, introduced by
Louis Désiré Blanquart-Evrard, was the most common kind of print in the latter half of the nineteenth century. Beautiful sepia gradation images were created by using albumen and silver chloride. The surfaces of prints made with this process were glossy because of the egg whites which were layered heavily to prevent the originally thin prints from curling, cracking, or tearing easily. This type of print was especially common for studio portraits and landscape or stereoviews.
1889: KallitypeDr. W. W. J. Nicol invented and refined the Kallitype. Vandyketype, or Single Kalliitype, is the simplest type of Kalltype and creates beautiful brown images.
1889: Film negativesCellulose nitrate film was developed by
Eastman Kodak in 1889 and refined in 1903. It is made of silver gelatin on a cellulose nitrate base. The negatives are flammable and therefore can be dangerous. Nitrate sheet film was used widely though the 1930s, while nitrate roll film was used through the 1950s. The nitrate base was replaced with
cellulose acetate in 1923. By 1937, Cellulose diacetate was used as the base, and beginning in 1947 Cellulose triacetate was used. Polyester film was introduced around 1960.
1935: Color photographsKodak introduced color film and transparencies in 1935. The first process was called
Kodachrome.
Ektachrome, introduced in the late 1940s, became equally popular. There are now a variety of color processes that use different materials; most consist of dyes (cyan, magenta, and yellow, each of which have different absorption peaks) suspended in a gelatin layer.
Photograph stability Photograph stability refers to the ability of
prints and
film to remain visibly unchanged over periods of time. Different photographic processes yield varying degrees of stability. In addition, different materials may have dark-storage stability which differs from their stability in light. ;Kodachrome: An extreme case with slides was stability under the intense light of projection. When stored in darkness, Kodachrome's long-term stability under suitable conditions is superior to other types of color film. Images on Kodachrome slides over fifty years old retain accurate color and density. Kodachrome film stored in darkness is largely responsible for excellent color footage of World War II, for example. It has been calculated that the yellow dye in Kodachrome, the least stable, would suffer a 20% loss of dye in 185 years. This is because developed Kodachrome does not retain unused color couplers. However, Kodachrome's color stability under bright light, especially during
projection, is inferior to substantive slide films. Kodachrome's fade time under projection is about one hour, compared to Fujichrome's two and a half hours. Thus, old Kodachrome slides should be exposed to light only when copying to another medium. ;Silver halide:
Black-and-white negatives and prints made by the
silver halide process are stable so long as the photographic substrate is stable. Some papers may yellow with age, or the
gelatin matrix may yellow and crack with age. If not developed properly, small amounts of
silver halide remaining in the gelatin will darken when exposed to light. In some prints, the black silver oxide is reduced to metallic silver with time, and the image takes on a metallic sheen as the dark areas reflect light instead of absorbing it.
Silver can also react with
sulfur in the air and form
silver sulfide. A correctly processed and stored silver print or negative probably has the greatest stability of any photographic medium, as attested by the wealth of surviving historical black-and-white photographs. ;Chromogenic:
Chromogenic dye color processes include Type "R" and
process RA-4 (also known as "type C prints"),
process C-41 color negatives. and
process E-6 color reversal (
Ektachrome) film. Chromogenic processes yield organic dyes that are less stable than silver, and can also leave unreacted dye couplers behind during developing. Both factors may lead to color changes over time. The three dyes, cyan, magenta, and yellow, which make up the print may fade at different rates, causing a color shift in the print. Modern chromogenic papers such as
Kodak Endura have achieved excellent stability, however, and are rated for 100 years in home display. ;Dye destruction:
Dye destruction prints are the most archival color prints, at least among the wet chemical processes, and arguably among all processes. The most well-known kind of
dye destruction print is the
Cibachrome, now known as
Ilfochrome. ;Ink jet: Some
ink jet prints are now considered to have excellent stability, while others are not. Ink jet prints using
dye-
pigment mixtures are now common in photography, and often claim stability on par with
chromogenic prints. However, these claims are based on
accelerated aging studies rather than historical experience, because the technology is still relatively young. ==Types and causes of deterioration==