Nitrate base, the pioneer of motion picture film bases, retired
from our cameras and laboratories about 1951-52. Still, its
very long shadow of distinguished commercial motion pictures
and film records haunts many film vaults. Nitrate base films
must be handled with informed care.
Cellulose nitrate base film is relatively unstable. If you
store it in large quantities of about 5,000 feet or more and in
non approved storage cabinets without proper ventilation, it
becomes a fire hazard. Admittedly, it takes a bit of pushing to
cause it to burst into flames spontaneously. For example, in
one laboratory test, combustion occurred with a decomposing
1,000 foot roll of film only after it was kept at 41°C (106°F)
for 17 days tightly encased in a can wrapped in insulation to
retain the heat of decomposition. However, even a minor fire
can cause major film losses. This example may not be that
different from some storage lofts in the summertime that are
uninsulated.
Cellulose nitrate decomposition is the villain. It shrinks,
even to the point of becoming unusable. Furthermore, as the
film breaks down, it gives off nitric oxide, nitrogen dioxide,
and other gases that yellow the film base, yellow and soften
gelatin, and oxidize the silver image. Later, the base cockles,
becoming very brittle and then sticky. Finally, it
disintegrates completely. This inevitable deterioration is
usually gradual, but elevated temperatures and humidity speed
it greatly.
While it deteriorates, nitrate base film makes a kind of
pressure cooker of the film can in which it rests, especially
when it's taped closed. If the gases can't escape, heat builds
and spontaneous combustion may not be far behind. Therefore,
nitrate film must never be closed in.
Escaping toxic gases (powerful oxidizing agents) can attack
nearby acetate and polyester base films, so store nitrate films
in their own special place and not in a place too heavily
concentrated.
If the conditions are right, their image layers may last for
decades or generations. Because of their great value, many
nitrate base films have been reprinted on current longer
lasting safety base. Somewhere, nitrate film is still with us,
so we offer a few more comments.
Probability of Rapid Decomposition
If you store old nitrate base films, the first thing you need
to check is the temperature of the storage area. High readings
of the temperature and/or the relative humidity are unfavorable
to nitrate and to other films. Are the by products of
decomposition being discharged from the storage area? Is there
too much nitrate in a confined area? The more rolls collected
in one place, the greater the chance of trouble. with nitrate
film, it's important to design separate and specialized storage
compartments.
Inspection and Segregation of Nitrate Base Film
Identification is the key to initiating the proper handling of
nitrate film. You need to properly identify the films in your
vaults and storage areas. Don't assume all films to be acetate
or polyester when some may be nitrate. Some rolls may be
spliced mixtures of each. Kodak never produced 16 mm or
narrower film on nitrate base. Some may have been slit to 16 mm
from 35 mm for whatever reason. Also, Kodak never produced 70
mm or 35 mm color camera original or color print films on
nitrate base, but they did produce on nitrate base a special
black and white Eastman nitrate film for use in making 35 mm
and 70 mm imbibition films (dyed by the Technicolor process).
It's important to know exactly what types of film are in your
possession because nitrate fumes and fire are a threat.
Conditions that may only marginally harm the acetate films can
cause a nitrate base to become very dangerous. Unless you can
detect some deterioration, you may have a hard time
differentiating nitrate from acetate base films. Edge
identification may establish the difference the easy way.
You can use ultraviolet lamps to identify EASTMAN Triacetate
Films by the resulting fluorescence. A different identification
tool is your nose. Cellulose nitrate has a characteristic acid
odor, similar to that of nitric acid. This odor is unmistakable
when a quantity of nitrate film has been stored, especially in
a nonventilated area.
Evaluating the Extent of Deterioration
The nitrate film you have in storage may be middleaged, but if
it was properly stored, it may be quite usable. However, if it
was neglected, it may be showing signs of early deterioration.
One way to determine the extent of deterioration is to look at
the color of the base. If it's yellowish, or even amber,
sulfiding has begun because of silver in the emulsion and some
yellowing of the gelatin. The confirming test is to see if the
film base is brittle and breaks easily on being bent in half,
especially with the emulsion side out. At this stage, the
gelatin is probably soft enough to dissolve readily if the film
is wetted.
If these symptoms of decomposition are found, handle the film
with care and keep it dry. Duplicate it soon after inspection,
drying, and cleaning, because buckled film and sticky gelatin
may make duplication later more difficult or perhaps
impossible.
Spontaneous Combustion
Spontaneous combustion is self ignition of combustible material
through chemical action (as oxidation) of its constituents. It
develops from knowable conditions, such as deterioration, and
with proper observation and care, you can prevent a chemical
reaction. Nonpreventive measures, whether it's in hay, oily
rags, or nitrate film, can result in a fire. With the
information given in this section, you can prevent the threat
of spontaneous combustion.
Apparently, fire isn't caused by cellulose nitrate in good
condition. But in the advanced stages of decomposition, self
ignition takes place at sustained temperatures only slightly
above 38°C (100°F). If undetected, heat producing deterioration
and high temperatures, with consequent heat buildup, coincide.
Such combustion isn't nearly so spontaneous as its name seems
to imply!
Storage Vaults and Conditions
Carefully examine all the materials known to be on nitrate
base. Detecting unstable nitrate film is by far the most
important way to preserve this material. If decomposition isn't
found quickly, complete destruction of the film record may
result. Spot inspection only needs to be done once a year if
you follow the recommended storage conditions, and once every 3
months if adverse conditions exist. Any nitrate film that is
badly buckled or sticky is in an advanced stage of
decomposition.
You may be able to duplicate some of these badly buckled or
deteriorated films, or they may yield a fair quality print.
Urgency is the word. If the film base is heavily stained and
moisture from our breath makes the gelatin slightly sticky, the
negatives or prints must be duplicated within 2 years while
maintaining proper storage conditions.
Never wet a decomposing nitrate base negative; the gelatin may
be readily dissolved. If you must remove surface dirt, use a
quality cleaner carefully. Many old negatives have an
iridescent dichroic or silver sulfide stain, usually on the
surface of the gelatin. This is a further sign of old and
deteriorated film.
Store these negatives only in small quantities and in different
locations. The production of chemical vapors and heat from
large concentrations of nitrate films demands special storage
conditions with a special exhaust and ventilation system. This
storage area should never be near safety films.
Never store any nitrate base materials in sealed containers or
without ventilation. Such dead storage simply increases the
rate of decomposition. Pack the reels loosely in ventilated
metal boxes or cabinets, and store them in a room apart from
all other photographic materials. Do not let the storage area
temperature exceed 21°C (70°F). If you achieve a lower
temperature without increasing relative humidity above 45
percent, that s even better. Relative humidity below 40 percent
retards decomposition even more, but makes the film more
brittle.
Help for Owners of Nitrate Base Film
Nitrate base films have been out of common use so long (since
about 1951-52) that expertise in handling them is not commonly
offered, but there are facilities that do offer this service.
Unless you are an expert concerning the characteristics of
nitrate films in various stages of decomposition, don't unroll
the films. Let the experts do it. For help determining the
historical (not monetary) value of any material on nitrate
base, contact a local historical film association or
International Film Archive, FIAF Secretariat, rue Franz Merjay
190, 1180 Brussels, Belgium. If they can't help you, they'll
direct you to someone who can. If the film has value or you
decide to have it duplicated, even if it isn't unique, one of
the film archives can give you advice on the procedures for
arranging duplication.
Dave Edgar
Cinematographer/Steadicam operator
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