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Photographs can be highly complex structures. To obtain
detailed information on identification, deterioration,
use, and treatment, it is best to consult the readings
listed for photographs.
Photographic prints and negatives can be composed of
a number of layers, including a support, binder (or
emulsion), and an image-forming component.
The support may be glass, metal, paper, or plastic.
Photographic prints have a paper support; resin-coated
(RC) prints are coated on both sides with polyethylene
to facilitate processing.
The binder is an adhesive-like
material that suspends and protects the image. The most
common 19th-century binders are albumen
(egg white) and collodion (guncotton). Gelatin
is the most common 20th-century binder.
Silver is the major image material for black and white
photographs, while color dyes make up modern color photographs,
prevalent since the 1940s. Negatives have been made
from glass, nitrate,
acetate, and now polyester.
Condition Concerns
Photographic materials are highly susceptible to deterioration
caused by handling, the environment (temperature, relative
humidity, light, atmospheric pollutants), and poor-quality
storage enclosures. Gelatin
binders are particularly susceptible to attack from
mold and insects.
Controlling light, relative humidity, and temperature
has the greatest impact in preserving photographic materials.
In particular, cold storage slows the deterioration
of film and color materials.
Specifications for storage enclosures outline the purity
of materials required for photographic materials; suitable
enclosures are those capable of passing the Photographic
Activity Test (PAT). A proper environment, suitable
enclosures, and conservation practices must be used
to maintain collections in good condition (see Conservation).
Diagnostic Tests
A-D Strips (available from Image Permanence Institute;
http://www.rit.edu/~661www1/)
provide a safe, simple method for detecting, measuring,
and recording the severity of "vinegar syndrome"
in acetate photographic film collections. Vinegar syndrome
is a slow form of chemical deterioration that causes
the film to shrink, buckle, and emit a strong vinegar
odor. A-D Strips are acid-base indicator papers that
change color in the presence of the acidic vapor given
off by degrading film. This provides an objective way
to document the extent of vinegar syndrome and helps
in deciding when acetate cinema film, microfilm, or
pictorial film needs to be duplicated.
Click here for a list
of relevant readings.
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Photographs
