Photographic materials have evolved since Louis Jacques Mandé Daguerre’s process[‡] of fixing images of the camera obscura was initially presented to a joint gathering of the Académie des Sciences and the Académie des Beaux-Arts in Paris, 1839 (Schwartz 2000: 4). The original daguerreotype (1840-1855) was a unique image on a plate of polished silver on copper, placed in a case and covered with a brass mat and glass. Ambrotypes (1855-1860; silver images on glass, bound by a collodion coating) and tintypes (1856-1920s; silver image on lacquered iron bound by collodion) were usually stored in similar cases. These early images should not be touched directly and be stored flat in acid and lignin free containers (Zanish-Belcher 1997: 1). These case photographs “are believed to be stable to light” with their protective cases (C.C.A 1990: 77).
Different care is necessary for prints, depending on their underlying physical structure and processes used to fix the image. The image of a photographic silver print “consists of finely divided silver metal contained in or on an organic colloid layer (albumen, collodion, gelatin, or starch), present as a discrete coating or as sizing, on a paper support” (Swan 1981: 271). The CCA guide recommends individual enclosures for each photograph as protection against dust, dirt, handling and the environment (C.C.A. 1990: 79). The CCA guide also recommends lignin-free and unbuffered paper storage such as envelopes or folders and inert uncoated polyester (mylar) storage such as sleeves, encapsulation, or sheet holders (C.C.A. 1990: 80).
Among the earliest photographs (1840s - 1860s) are salt prints: paper “treated with solution of sodium chloride, dried, and treated with silver nitrate solution, forming silver chloride in and on the surface of the paper.” (Swan 1981: 272) These prints are unique in that the silver particles are directly on the paper. Common signs of deterioration of these prints include faded edges, yellowing, and surface deposits (i.e. dirt). Caring for these prints includes avoiding exposure to unnecessary light, providing low-humidity storage and surface protection in the form of mylar interleaving sheets for matted prints (placed between the mat and the print) and mylar sleeves with rigid supports for unmatted prints (Swan 1981: 273).
The artist's van; Marcus Sparling, full-length portrait, seated on Roger Fenton's photographic van; photographic print : salted paper ; 17.5 x 16.5 cm; Fenton, Roger, 1819-1869, photographer;[LC-USZC4-9240 (color film copy transparency) LC-USZ62-2319 (b&w film copy neg.)] <http://hdl.loc.gov/loc.pnp/cph.3g09240> Salted paper prints 1850-1860.
The discovery and embrace of photography in these initial years revolved around science and travel. Daguerre’s camera obscura was in the process of becoming an indispensable “means of extending the powers of human observation” (Schwartz 2000: 5). Photographs were considered a breakthrough in their reliability and evidential authenticity as direct and detailed exact copies of objects from nature allowing for a new way of knowing and representing the world across space and time for explorers and scientists as well as “a surrogate for travel” (Schwartz 2000: 13). It is ironic that today’s digital imaging technology is often imbued with similar enthusiasm for its ability to skip through the physical materiality of the image altogether and remain entirely in the virtual realm.
In addition to salt prints, there are early (1850s – 1920s) albumen (sodium chloride solution with egg whites) prints such as those of Muybridge, Watkins, Jackson and O’Sullivan (Swan 1981: 273). Signs of deterioration of these prints include curling, the formation of a network of fissures (unevenly shaped segments) on the albumen, cleavages between these segments through which underlying paper is visible, and segment cupping (albumen pulls up at edges) (Swan 1981: 274). Water treatments increase the cleavages as the print dries which rules out wet mounting and leaves the use of mylar interleaving sheets tacked over the print to restrain curling (Swan 1981: 278). In order to avoid the ‘pinch’ and creases resulting from handling of these prints, Swan recommends secure attachment to rigid supports (Swan 1981: 279). Salt and albumen prints as well as early RC papers are particularly susceptible to fading and should be kept in darkness as much as possible (C.C.A. 1990: 78).
Salt Lake City, Utah. by Jackson, William Henry, 1843-1942, photographer; photographic print mounted on mat board : albumen ; image 42.8 x 53.5 cm; [LC-USZ62-119588 (b&w film copy neg.)] <http://hdl.loc.gov/loc.pnp/det.4a32595> Albumen prints.
The Horse in motion. "Sallie Gardner," owned by Leland Stanford; running at a 1:40 gait over the Palo Alto track, 19th June 1878 / Muybridge, Eadweard; c1878; print on card : albumen; [LC-USZ62-45683 (b&w film copy neg. of copy 2)] <http://hdl.loc.gov/loc.pnp/cph.3a45870>
Mirror Lake, Yosemite by Watkins, Carleton E., 1829-1916; albumen print; [San Francisco : Carleton E. Watkins, ca. 1879]. [LC-DIG-stereo-1s01356 (digital file from original photo, front)] <http://hdl.loc.gov/loc.pnp/stereo.1s01356>
Collodion (cellulose nitrate) prints were also made in this early period between 1890s-1910s. They are recognizable by their ‘plastic’ glossy feel that is impermeable to water and showing no fissures (Swan 1981: 279). Preservation of these prints calls for rigid supports (museum board) and surface protection (mylar mats) against abrasion and dirt (Swan 1981: 279).
[Panoramic view of Spearfish, S.D.]; collodion printing-out paper ; 7 x 34.5 in.; c1902. [pan 6a09776] <http://hdl.loc.gov/loc.pnp/pan.6a09776>
Since the 1870s, the dominant printing has been done on multi-layer gelatin prints. These can be differentiated from albumen prints through lack of fissuring and from collodion prints by their permeability to water (Swan 1981: 280). Relative humidity control is crucial to prevent curling, warping and deforming caused by the different rates of expansion and contraction of the layers [§] (Swan 1981: 281). Mylar sleeves and interleaving can cause contact spots on gelatin prints so packaging modifications need to be introduced to lift the mylar window away from the print surface (Swan 1981: 284). Furthermore, residual thiosulfate from the fixing process is a particularly acute problem for gelatin prints due to the retentiveness of the gelatin, causing fading and yellowing with time (Swan 1981: 289). ‘Careful rewashing procedures’ can correct this problem (Swan 1981: 290).
Seventy-one years, or, My life with photography. Study of sunlight and shadow by Gottscho, Samuel Herman; photographed 1916, printed later; silver gelatin print. [LC-USZC2-4154] <http://hdl.loc.gov/loc.pnp/gsc.5a00047>
Colour prints (and negatives) introduce the new difficulty of dyes which fade more quickly over time than black & white. All photographs are a result of chemical reaction with light so it is obvious that a lifespan of a photograph can be measured in exposure to light. As a result, photographs should not be placed on display for more than a year even in dimmed (50 lux) light (Wilson Part 1 1998: 5).
Dry mounting using heat-set adhesives was a popular archival preservation method in the 1960s that should be avoided on original prints because it causes splitting of layers in gelatin prints, severe fissuring and cleavages in albumen layers and darkening and scorching of salt prints (Swan 1981: 283). The CCA guide warns against trying to remove photographs from mounting boards in favour of mylar encapsulation ‘as is’ with additional board support, as well as against trying to unroll photographs without a professional conservator (C.C.A. 1990: 80). Steel shelves, cabinets and drawers are preferable to wooden storage for chemical reasons (C.C.A. 1990: 80).
[‡] the process was based on the work of Joseph Niéphore Niépce who used a camera obscura to fix an image on stone in 1824. (Zanish-Belcher)
[§] emulsion and binder expand the most and the paper base the least (Swan 1981)