Photograph stability
Encyclopedia
Photograph stability refers the ability of a photographic print or photographic film
to remain visibly unchanged over periods of time. Different photographic processes yield varying degrees of stability.
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 historical black-and-white photography.
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.
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
.
-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.
Photographic film
Photographic film is a sheet of plastic coated with an emulsion containing light-sensitive silver halide salts with variable crystal sizes that determine the sensitivity, contrast and resolution of the film...
to remain visibly unchanged over periods of time. Different photographic processes yield varying degrees of stability.
Silver halide
Black-and-whiteBlack-and-white
Black-and-white, often abbreviated B/W or B&W, is a term referring to a number of monochrome forms in visual arts.Black-and-white as a description is also something of a misnomer, for in addition to black and white, most of these media included varying shades of gray...
negatives and prints made by the silver halide
Silver halide
A silver halide is one of the compounds formed between silver and one of the halogens — silver bromide , chloride , iodide , and three forms of silver fluorides. As a group, they are often referred to as the silver halides, and are often given the pseudo-chemical notation AgX...
process are stable so long as the photographic substrate is stable. Some papers may yellow with age, or the gelatin
Gelatin
Gelatin is a translucent, colorless, brittle , flavorless solid substance, derived from the collagen inside animals' skin and bones. It is commonly used as a gelling agent in food, pharmaceuticals, photography, and cosmetic manufacturing. Substances containing gelatin or functioning in a similar...
matrix may yellow and crack with age. If not developed properly, small amounts of silver halide
Silver halide
A silver halide is one of the compounds formed between silver and one of the halogens — silver bromide , chloride , iodide , and three forms of silver fluorides. As a group, they are often referred to as the silver halides, and are often given the pseudo-chemical notation AgX...
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
Silver
Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...
can also react with sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
in the air and form silver sulfide
Silver sulfide
Silver sulfide, Ag2S, is the sulfide of silver. This dense black solid constitutes the tarnish that forms over time on silverware and other silver objects. Silver sulfide is insoluble in all solvents, but is degraded by strong acids. Silver sulfide features a covalent bond, as it is made up of...
. A correctly processed and stored silver print or negative probably has the greatest stability of any photographic medium, as attested by the wealth of historical black-and-white photography.
Chromogenic
ChromogenicChromogenic
Chromogenic refers to color photographic processes in which a traditional silver image is first formed, and then later replaced with a colored dye image.- Description :...
dye color processes include Type "R" and process RA-4
RA-4 process
RA-4 is Kodak's proprietary name for the chemical process most commonly used to make color photographic prints. It is used for both 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...
(also known as "type C prints"), process C-41
C-41 process
C-41 is a chromogenic color print film developing process. C-41, also known as CN-16 by Fuji, CNK-4 by Konica, and AP-70 by AGFA, is the most popular film process in use, with most photofinishing labs devoting at least one machine to this development process....
color negatives. and process E-6
E-6 process
The E-6 process is a chromogenic photographic process for developing Ektachrome, Fujichrome and other color reversal photographic film....
color reversal (Ektachrome
Ektachrome
Ektachrome is a brand name owned by Kodak for a range of transparency, still, and motion picture films available in most formats, including 35 mm and sheet sizes to 11x14 inch size. Ektachrome has a distinctive look that became familiar to many readers of National Geographic, which used it...
) 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 destructionDye destruction
Dye destruction or dye bleach is a photographic printing process, in which dyes embedded in the paper are bleached in processing. Because the dyes are fully formed in the paper prior to processing, they may be formulated with few constraints, compared with the complex dye couplers that must react...
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
Dye destruction
Dye destruction or dye bleach is a photographic printing process, in which dyes embedded in the paper are bleached in processing. Because the dyes are fully formed in the paper prior to processing, they may be formulated with few constraints, compared with the complex dye couplers that must react...
print is the Cibachrome, now known as Ilfochrome
Ilfochrome
Ilfochrome is a dye destruction positive-to-positive photographic process used for the reproduction of slides on photographic paper. The prints are made on a dimensionally stable polyester base, essentially a plastic base opposed to traditional paper base...
.
Ink jet
Some ink jet prints are now considered to have excellent stability, while others are not. Ink jet prints using dyeDye
A dye is a colored substance that has an affinity to the substrate to which it is being applied. The dye is generally applied in an aqueous solution, and requires a mordant to improve the fastness of the dye on the fiber....
-pigment
Pigment
A pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which a material emits light.Many materials selectively absorb...
mixtures are now common in photography, and often claim stability on par with chromogenic
Chromogenic
Chromogenic refers to color photographic processes in which a traditional silver image is first formed, and then later replaced with a colored dye image.- Description :...
prints. However, these claims are based on accelerated aging
Accelerated aging
Accelerated aging is testing that uses aggravated conditions of heat, oxygen, sunlight, vibration, etc. to speed up the normal aging processes of items. It is used to help determine the long term effects of expected levels of stress within a shorter time, usually in a laboratory by controlled...
studies rather than historical experience, because the technology is still relatively young.
General
- Basics of Photograph Preservation
- Preservation and Archives Professionals
- Care, Handling, and Storage of Photographs, Library of Congress
- The Care and Preservation of Photographic Prints, The Henry Ford Museum
- Preservation of Photographs: Select Bibliography, Northeast Document Conservation Center
- Caring for Your Photographs, The American Institute for Conservation of Historic and Artistic Works (AIC)