cesses will even deteriorate in the dark). This must
be taken into account when exposing negatives,
viewing transparencies, and displaying prints. The
brightness of light, the length of time the image is
exposed, and the type of light can all have an
adverse affect. Brightness and duration are related
as prolonged exposure in low lighting can be as
harmful as a brief flash of bright light. Sunlight
contains the most damaging type of light in the
form of ultraviolet (UV) rays. These should be
filtered out where possible and tungsten lamps are
preferable for display and exhibition. Resin or plas-
tic coated prints are more susceptible to light than
archivally processed fiber prints. In order to max-
imize the life of a black and white print, illumina-
tion at 50 lux is recommended during display; there
should be a maximum intensity of no more than
100 lux. Color photographs are particularly vulner-
able to light and are ideally illuminated at 30 lux
and never more than at 70 lux. Light meters should
be used to check ambient light levels. In museum
and gallery settings light levels are strictly con-
trolled, and the length of time photographs are on
view carefully observed.
Transparencies in the form of slides can fade
after only 10 minutes in a projector, and it is advi-
sable to preserve the original by using good quality
duplicates for viewing.
Heat and Moisture
Heat and moisture both affect photographic
materials. Too much moisture in the air can pro-
duce chemical changes in the emulsion and encour-
age the growth of mould—too little can cause
emulsions, and papers and plastics to become brit-
tle, flake, and crack. High temperatures also pro-
mote chemical changes, particularly in color film.
Again there is a link between moisture content of
the air, known as relative humidity (RH) and tem-
perature. A stable RH of 20% to 50%, (20% to 30%
for color stock) is most desirable combined with a
consistent temperature of no more than 21 C, and
even lower (8–12 C) for color, but any reduction is
helpful. Fluctuations in temperature and RH are
extremely damaging as they constantly stress the
materials and maintaining a stable environment is
essential. Cold storage, including freezing, is
increasingly used for preserving photographs. The
photographs are placed in tightly sealed bags or
containers to avoid fluctuations in RH. When
taken out of cold storage the package should be
left at room temperature to acclimatize before
opening to prevent condensation forming in the
cold image surface. However this is only really sui-
table for photographs that are not often accessed.
Collections should be checked for signs of dete-
rioration. Once every five years is appropriate,
more often in the case of nitrocellulose film stock.
Things to check are: physical damage including
tears, cracks, and flaking emulsion: chemical
changes such as discoloration and pungent odors:
and environmental problems from air pollution,
mould, and insect or rodent attack. Damaged
items should be stored separately until treated, as
mould and gases and pollutants from chemical
changes can quickly spread to adjacent images.
Temperature and relative humidity should also be
carefully and regularly monitored.Handling
One of the most overlooked, and yet simplest,
aspects of preservation is correct handling. In an
ideal world photographs would never be handled at
all. Obviously this is impractical but a general goal
should be a reduction in the handling of both
negatives and prints. As fingerprints leave perspira-
tion and oily stains that can permanently mark the
image and also cause chemical changes in the emul-
sion, it is recommended that photographs and
negatives be handled with clean hands and prefer-
ably lint free cotton gloves. The emulsion surface
should be avoided (in negatives the emulsion is the
shiny side) and prints should be supported with
two hands. Transparent plastic sleeves allow prints
and transparencies to be viewed while safely pro-
tecting them from direct contact.
Prints should never be rolled as this puts a strain
on the emulsion. Conversely attempts to to unroll
and flatten rolled or curled prints should be
avoided, as this can cause the surface to crack or
wrinkle. If prints or negatives are stuck together
attempts to separate them should be left to the
conservator, as should flattening curled prints.
Although historically, many fine art photogra-
phers sign their works in ink directly on the photo-
graph, generally it is preferable to keep ink pens,
especially felt tip and other water based inks, away
from photographs. Ideally any information should
be written on the mount or enclosure. If it is
necessary write on the back of the print, a soft
pencil should be used, and care taken not to mar
the print. Paperclips, pins, rubber bands, and pres-
sure sensitive tape should never be used. They can
only result in physical damage, rust stains, chemi-
cal damage from sulfides in the rubber, and stain-
ing from glue residues.CONSERVATION