Kodak D-31 - Manual (Page 11)

8 D-31 June 2002
Humidification
Humidification is not necessary or desirable
unless the prevailing relative humidity is under
15%—under 30% for polyester-base films—for
long periods of time and unless the film is used
frequently and physical troubles are encountered.
Neither water trays nor saturated chemical
solutions should be used for humidification of
storage cabinets because of the more serious
danger of overhumidification. Even humidification
controlled by instrumentation is risky unless
“fail-safe” devices are installed.
Fungus Growth
Fungus spores are found in the air everywhere.
They germinate and grow under favorable
conditions. When silver-gelatin films are stored for
any length of time in an atmosphere having a
relative humidity of above 60%, fungus (often
called mold or mildew) has a tendency to grow on
the emulsion surface, the back of the film, or on
the film reel. The higher the relative humidity, the
greater the chance of fungus attack and the more
abundant its growth. The only real protection
against fungus growth is to make certain that
conditions are unfavorable for its growth.
If fungus growth progresses far enough, it can
cause serious and permanent damage to film.
This takes the form of distortion of the emulsion
and eventually causes chemical breakdown so
that the gelatin becomes sticky and readily soluble
in water. Water or water solutions should not be
used for the removal of fungus growth because
either may lead to disintegration of the image.
Clean affected film by wiping it with a soft plush
or cotton pad moistened with an approved
film-cleaning liquid, such as isopropyl alcohol.
This procedure is described in detail in a separate
Kodak Pamphlet.
10
Fungus can grow on most surfaces, including
diazo and vesicular films; however, these films are
more resistant to fungus growth than silver-gelatin
films. If necessary, clean these film types by
wiping with a soft, plush or cotton pad, moistened
with water. Do not use solvents on diazo,
vesicular, or thermally processed silver films.
The Kodak Disaster Recovery Laboratory
offers no charge evaluation of suspect microfilm
and can be reached at 1-800-EKC-TEST
(1-800-352-8378) or 1-585-253-3907.
Microscopic Blemishes
Some processed silver-gelatin microfilms in
storage for two to twenty years have developed
microscopically small colored spots or blemishes.
The fogged leader at the outside of the roll is most
frequently affected by the blemishes, which are
generally red or yellow in color and smaller in size
than the image characters (e.g., a typewritten
letter reduced 20X) on the microfilm. On occasion,
these spots progress further into the roll and
appear in image areas. A more detailed
description of the blemishes and of the techniques
used in inspecting microfilm is given in National
Bureau of Standards Handbook 96.
11
The spots are caused by local oxidation of image
silver, resulting in the formation of minute deposits
of yellow- or red-colored colloidal silver.
12,13
Possible oxidizing agents entering from outside
the roll of microfilm are aerial oxygen, whose
action on the film is strongly accelerated by
moisture, and atmospheric contaminants such
as peroxides, ozone, sulfur dioxide, hydrogen
sulfide, and nitrogen oxides, which all occur in
industrial atmospheres.
Assuming that your microfilm was processed to
established quality control standards, microscopic
blemishes (redox) may occur due to the oxidation
of the metallic silver image by the presence of
oxidants in the storage area: peroxides, ozone,
nitrogen oxides, oil-based paint fumes, organic
solvents, floor-cleaning agents, cardboard
cartons, excessive temperature and humidity,
or a variety of other materials that generate
peroxides which attack silver microfilms.
The use of low concentrations of potassium
iodide in the fixing bath (0.2 g/L) has been
recommended and has been found to provide
a good degree of protection against these
blemishes.
13 Kodak Microfilm and Prostar Fix
Solutions contain this stability-enhancing iodide.
Once the deterioration of the microfilm occurs,
it cannot be reversed. Silver film duplication,
Kodak Brown Toner, and the use of molecular
sieves can be used to stabilize the reaction.