| Before storage,
all nitrate base film should be carefully examined
to determine its condition. Visual examination of
nitrate film will detect major physical difficulties,
but decomposition will be detected only after some
damage has occurred. The sense of smell is more
useful in detecting the earlier stages of nitrate
decomposition because the nitrogen oxide fumes given
off have a characteristic pungent odor similar to
that of nitric acid. If any signs of decomposition
are present, it should be cleaned, duplicated on
a safety base film and then destroyed. Nitrate
base film still in good condition should be cleaned
if necessary and each roll place in separate film
can. Aluminum or stainless steel is preferable
to tinned steel. Cans in which nitrate base film
is stored should never be taped or otherwise sealed,
as this would prevent the escape of nitrogen oxide
gas, which accelerates decomposition of the film.
Care should also be taken to insure that no acetate
or polyester base film is stored in the same can
as the nitrate film. Unstable or decomposing nitrate
film produces nitrogen dioxide gas, which has
a three-fold effect on acetate film. The first
stage discolors the starts to fade the image,
then the gelatin of the emulsion is attacked and
degraded and finally the base begins to decompose.
A simple and effective method
of rapidly distinguishing between intermixed nitrate
and acetate base films in a single roll is to
view the edge of the wound up roll with an ultraviolet
lamp. The nitrate base film appears black and
the acetate appears bluish purple.
Another method of identifying
nitrate base film is to check the visible frame
line mark on processed film. The frame mark is
orientated lengthwise between the perforation
on safety film and widthwise between the perforation
on nitrate film.
The final conclusive test of
nitrate versus safety film is a burning test that
can be made safely if certain precautions are
taken. Cut a piece of film approximately 16mm
wide and 35mm long. Bend the film lengthwise and
crease it sufficiently so that, when released,
it will stand upright. Stand the film with the
crease vertical on a flat surface. This should
be a safe distance from all film stocks. With
a match flame, ignite one of the top corners of
the film. If the film ignites easily, burns down
rapidly and vigorously with a bright yellow flame,
and is completely consumed in less than 15 seconds,
it probably is cellulose nitrate. If it ignites
with difficulty and takes more than 15 seconds
to be completely consumed, it is probably safety
base film.
Each roll of safety film should
be visually examined on rewinds. Such a check
will reveal major physical difficulties such as
fluting, buckle, twist, curl, spoking, fungus
growth, or severe color fading. Film that has
been properly stored will exhibit a minimum of
these effects. Film that has been subjected to
extreme variations in temperature and humidity
could exhibit several of these defects.
All films, color or B &
W, can be damaged by mildew or fungus growth.
When film is stored for any length of time at
RH above 60%, some fungus is likely to grow on
the surface of the emulsion or support.
If discovered in time, steps
can be taken to remove it. If the growth has gone
too far, it may have caused permanent damage to
the image.
Water or water solutions should
not be used for the removal of fungus growth because
such growth on the emulsion side causes a solubilizing
of the gelatin. The use of water or water solutions
will lead to disintegration of the image.
When the gelatin has become
etched or distorted by the fungus growth, there
is no satisfactory method of restoration. topˆ |
