|
In general, photographic prints are composed of at
least two distinct layers. The uppermost layer is referred to as the emulsion
layer. The emulsion layer generally consists of metallic particles or
dyes held in binder such as gelatin. This layer forms the image of the
photograph. The lower layer or "support layer" is usually composed
of paper, glass, metal, or plastic.
Black and White Prints - Black and white photography
is the oldest photographic process. Commonly, the emulsion layer will
consist of fine particles of silver embedded in a layer of binder. While
the most common binder was and continues to be gelatin, other binder materials
include albumen and collodian.
Color Prints - Color photography was invented
in 1935 by the Eastman Kodak Company. There are a large variety of color
processes that involve different materials but most consist of dyes suspended
in a gelatin layer.
CAUSES OF DETERIORATION
& GUIDELINES FOR CARE
Deterioration can be caused by inappropriate light,
temperature or humidity levels, poor processing, inappropriate framing,
pollution and contaminants, mishandling, pests and mold. In addition,
inappropriate repairs and cleaning methods can cause irreparable damage
to photographic prints.
TEMPERATURE AND HUMIDITY
Both color and B & W photographs are prone to damage
from exposure to high and/or fluctuating temperature and relative humidity
levels. High temperature and humidity levels combined with pollution and
contaminants can cause fading of photographic images. Excessively low
humidity levels can cause photographs to curl due to dryness. Conversely,
high humidity can lead to mold growth. The recommended levels for storage
of photographic prints are 30-50% relative humidity at temperatures of
58-68 degrees F. Fluctuations of more than 5 degrees per day should be
avoided. Cold storage at low relative humidity is the ideal storage environment
for color photographs; however, this is not usually practical for most
collectors. Inexpensive temperature and humidity sensors can be purchased
from conservation suppliers.
LIGHT
Photographs are prone to light damage in the form of
fading. In general, color photographs are more sensitive than B &
W prints. For this reason, color photographs should be displayed under
low light levels (approximately 50 Lux.). B & W photographs can be
displayed under slightly higher levels. The light meter of a 35 mm camera
can be used to measure light levels. Ultra violet, which is the most damaging
form of light, should be eliminated by using ultra violet filtering glass
or Plexiglas on framed prints.
POLLUTION AND CONTAMINANTS
Since most B & W photographic images are composed
of silver particles, they are prone to degradation through metallic corrosion.
The same chemical pollutants that cause silver to tarnish can cause the
degradation of photographic images. Whenever possible, contact with pollutants
such as sulfur, ozone or peroxides should be avoided. Since materials
like rubber and leather contain large amounts of sulfur they should not
be stored in closed containers or drawers with photographs. The dyes in
color photographs can also be damaged by contact with chemical pollutants.
DISPLAY
Proper framing can help to increase the life of photographs.
Prints should be framed using acid-free, lignin-free rag mat board. A
window mat should always be placed between the print and the glass in
a picture frame. The mat will serve to prevent the prints from becoming
stuck to the glass. Only archival-quality adhesive tapes should be used
for framing. Recommended tapes include filmoplast and acid-free linen
tape. They are both available from Light Impressions Inc. (see suppliers
list attached). Ordinary masking and scotch tape should be avoided since
they can degrade and discolor leading to stains.
STORAGE AND HANDLING
The best protection for photographic prints is storage
in clear mylar (plastic) envelopes. The mylar helps to minimize damage
during handling. For added protection, acid-free envelopes and boxes are
available from conservation suppliers. When purchasing plastic sleeves
make sure that they are uncoated mylar or polyethylene. Other materials
such as polyvinylchloride can damage photographs.
When it is necessary to write on photographs, inscriptions
should be written in pencil along borders or on the back of photographs.
It is important to use a hard surface to write on and to press lightly
so as to avoid leaving an embossed impression on the print. Ink pens should
never be used since they can bleed through and permanently obscure the
image.
CLEANING AND CONSERVATION
Surface dirt should be removed
using a soft brush. More extensive cleaning and repair should be left
to a professional conservator since photographs are easily damaged by
moisture and solvents.
Useful Links:
Photo collections by Andrew Prokos:
|
