Kodak D-31 User Manual

Micrographic Quality

D-31

Storage and
Preservation
of Microfilms

Contents

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Electronic Imaging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Record Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Storage Hazards and Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Fire Protectio n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Storage Vaults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Cabinets and Safes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Effects of High Temperatures . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Water Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Effects of High and Low Relative Humidities . . . . . . . . . . . . . . . . . . 5

High Humidit y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Low Humidity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Molecular Sieves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Humidity Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Air Conditioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Moisture-Tight Containers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Humidification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Fungus Growth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Microscopic Blemishes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Toning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Chemical Contamination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Composition of Enclosure Materials . . . . . . . . . . . . . . . . . . . . . . . 10

Paper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Plastic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Metal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Adhesive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Printing Inks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Theft Protec tio n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Processing for Permanence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Silver-Gel a tin F ilms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Fixing Baths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1

Washing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Squeegees . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Drying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Washing Aids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Residual Hypo Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Residual Silver Compound Test . . . . . . . . . . . . . . . . . . . . . . . . 12

Protective Coatings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

D-31 June 2002 i

Processing of Other Film Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Thermally Processed Silver (TPS) . . . . . . . . . . . . . . . . . . . . . . . . 13

Diazo Films . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Vesicular Films . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Special Storage and Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Underground Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Effects of Nuclear Ex p lo s io n s . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Time-Capsule S torage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Handling and F iling Film Records . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Interfiling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Table 1: Applicable Standards for Microfilm . . . . . . . . . . . . . . . . . 15

Table 2: Storage Life of Microfilms . . . . . . . . . . . . . . . . . . . . . . . . 16

Table 3: Storage Temperature and Relative Humidity . . . . . . . . . . 17

Summary of Requirements for Storage and

Preservation of Records on Kodak Microfilm . . . . . . . . . . . . . . . . . 17

Storage Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

References and Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

ii D-31 June 2002

Introduction

Definitions

Photographic film remains an important
documentary material. The increasing quantity
and value of microfilm records used in financial
institutions, libraries, government offi ces, and
industrial firms have focused attention on the
care of such records to make certain that they
last as long as possible.

The distinction between phot ographic film recor ds
intended for storage and those intended for use
has not always been clear. Use or work copies
are the predominant photographic records found
in libraries or record centers and are subject
to much handling due to their value as quick
references. However, because of this handling,
they are subject to dirt, abrasion, fingerprints,
contamination with foreign materials, and
exposure to excessive light, temperatures, and
harmful atmospheric pollutants. As a result, these
copies in daily use cannot be considered suitable
for long-term preservation. For lo ng-t erm stor age,
it is imperative to prepare duplicate copies that
meet certain criteria, such as proper filming,
duplicating, processing, minimum handling,
controlled environment, and storage.

In general, the care needed for storing
photographic records is similar to that for
storing written paper records, although there
are some requirements peculiar to the storage
of photographic film.

The permanence of photographic records
depends on the chemical stability of the film,
how the film is processed, and the conditions
under which the processed film records are
stored. The stability of the film layers is
determined in manufacture and processing, while
storage is controlled by the user. This pamphlet
discusses the composition and properties of
black-and-white silver-gelatin, thermally
processed silver (TPS), diazo, and vesicular films
as they relate to film permanence. It also
describes the essential requirements of good
processing and storage practices.

NOTE:Refer to the latest revision of each ANSI or

ISO Standard specified.

To help understand storage requirements,
the composition and structure of microfilm are
described and definitions of commonly used

1

terms are given.

Structure of a typical black-and-white negative film.

Acetate film—(acetate base) safety film with a
base composed principally of cellulose acetate
or triacetate.

Antihalation undercoat—separate layer of
light-absorbing dye located between the film
emulsion and the base to suppress li ght reflection.
During processing of this film, the dye layer
becomes transparent.

Base or support—a flexible plastic material tha t
is coated with a thin, light-sensitive, image­forming layer. The thickness of the base varies
with different film types.

Dimensional stability—ability of photographic
materials to maintain their origina l size and shape
during and after processing and also under
various conditions of temperature and humidit y.

Emulsion—the image-forming layer. For
unprocessed black-and-white silver-gelatin films,
it is composed primarily of minute silver halide
crystals suspended in gelatin. Exposure to
light in a camera or printer causes no visible
effect, but there is an invisible change which
produces a “latent image.” To obtain a visible,
usable image, the exposed material must be
chemically processed.

For diazo and vesicular films, the sens itized layers
are composed of light-sensitive diazonium salts.
To obtain a visible, usable image with these films,
the exposed material is heat-processed. Diazo
films are typically heat-processed in the presence
of ammonia.

For TPS films, the image-forming la yer is ty pic all y
silver halide and silver salts suspended in a
polymeric binding.

D-31 June 2002 1

Emulsion layer(s)—image or image-forming
layer(s) of photographic films, papers, and plates.

Film base—the plastic support for the emuls ion
and backing layers.

Halation—halo or ghost around the desired
image on a photographic emulsion. (This is
caused by the reflection of rays of light fr om th e
base to the emulsion or by internal scattering of
light within the film.)

Nitrate film—a photographic film with a base
consisting of cellulose nitrate. Nitrate-base films
decompose with age and are not suitable for
permanent records. The manufacture of nitrate
film by Eastman Kodak Company in the United
States of America was discontinued in 1951, but
older nitrate motion-picture fil ms are often found in
storage. It is not always possible to determi ne by
visual examination if a film has a nitrate base.
However , neither KODAK nor RECORDAK
Microfilms in any width were ever made on
nitrate base.

Non-curl backing layer—a layer, usually made
of gelatin, applied to the side of the film base
opposite to that of the emulsion layer, for the
purpose of preventing curl.

NOTE:It is comparable to the emulsion layer

in thickness and is not removed in
processing. (Antihalation or other
layers removed in processing are
excluded from this definition.)

Polyester film—a photographic film having a
polyester base. This type of base manufactured
by Eastman Kodak Company is called Estar Base.
It is exceptionally tough and strong and has
excellent dimensional stability. Microfilm
emulsions on Estar Base are currently supplied
for many purposes. Kodak currently manufact ures
only microfilms on Estar Base.

Safety photographic film—photographi c film
which passes the ignition time test and burning
time test as specified in ANSI and ISO Standards.

Safety poly(ethylene terephthalate ) base—
a polyester film base for recording materials
composed mainly of a polymer of ethylene
glycol and terephthalic acid. All safety films
(both acetate and polyester) manufactured
by Eastman Kodak Company meet these
requirements. This means that they are
difficult to ignite and are slow burning.

All silver-gelatin Kodak Microfi lms on Estar Base,
when processed as recommended by Kodak,
meet the current specific ations established by the
American National Standards Institute, Inc.,
(ANSI) for films intended for use as LE 500.

Substratum (subbing or precoat)—the layer
that bonds the emulsion to the base.

Electronic Imaging

With the coming of electronic digit al imaging
systems, the need for continuing the quality
concepts already est ablished i n the micrograph ics
arena has evolved. Following are a few
key concepts.

Digitization—use of a scanner to convert
documents (on paper or microforms) to
digitally coded electronic images suitable
for electronic storage.

Digital—the use of binary code to record
information. “Information” can be text in a binary
code (e.g., ASCII), images in bitmapped form,
or sound in a sampled digital form or video.

NOTE:Information is recorded digitally for

accuracy in storage and transmission.
Some types of data manipulation are
easier in digi tal form.

Scanning—1.) In electronic imaging, scanning is
the operation which precedes digitization, where
the surface of a document is divided into pixels
and analog values are collected representing the
optical density (brightness and possibly color)
of each pixel.

2.) In electronic imaging, OCR scanning is the
conversion of marks that represent symbols into
symbols for use in a data processing system.
The paper or microfilm with the human-readable
marks is first scanned as an image, then is
analyzed to recognize the intended symbol.
The result is the set of symbolic information,
in a machine-readable code such as ASCII
(also known as handprint character recognition,
intelligent character recognition, and optical
character recognition).

3.) In micrographics, sca nning is the movement of
an image on a reader screen in a direction
perpendicular to the direction of r oll-fil m transport.

4.) Scanning is the systematic examination of
data (ISO).

2 D-31 June 2002

Scanner—a device that electro-optically conver t s
a document into a series of pixels by detecting
and measuring the intensity of light reflected or
transmitted. When initially captured, each pixel is
a level of brightness (gray or color), initially an
analog quantity, but potentially digitized.

NOTE:For many applications, total information

about each pixel is not needed and would
represent a burdensome amount of output
from the scanner. Therefore, most
scanners digitize the value of each pixel
and reduce the amount of data output to
only that which is required. For example,
output might be limited to one bit per pixel
for “black-and-white” scanning.

Scanner threshold—the brightness level above
which a pixel is considered pure white and
below which the pixel is considered pure black
(sometimes set manually [lighter/darker
setting], or set automatically based on the
average brightness of the document).

Record Classification

On the basis of required retention, photographic
records can be classified broadly as requiring
medium-term storage and long-term storage.

Archival medium—recording material tha t can
be expected to retain information forever, so
that such information can be retrieved without
significant loss when properly stored. However,
there is no such material and it is not a term to be
used in American National Standard material or
system specifications.

Life expectancy (LE)—the length of time that
information is predicted to be retrievable in a
system at 21°C and 50% RH.

LE designation—the rating for the “life
expectancy” of recording materials and
associated retrieval systems.

NOTE:The number following the LE symbol is a

prediction of the minimum life expectancy,
in years, for which information can be
retrieved without significant loss when
stored at 21°C and 50% RH.

Extended-term storage conditions—storage
conditions suitab le for the preservation of
recorded information on the majority of freshly
processed photographic films for 500 years .

Medium-term storage conditions—storage
conditions suitab le for the preservation of
recorded information for a minimum of 10 years.

Methylene blue—a chemical dye formed
during the testing of permanence of processed
microimages using the methylene-blue
method. Also called residual thiosulfate ion
and silver densitometric method.

Storage Hazards and Protection

There are a number of hazards to the sat isfactory
storage of photographic film that apply to records
intended for medium-term, long-term, or
extended-term storage. In fact, it is not always
possible to predict the desired life of recor ds at the
time they are made.

While films of medium-term, long-term, or
extended-term interest are subject to the same
hazards, the storage protection provided for
them will differ in degree because of a number
of factors. These include the cost of providing
storage facilities, desired record life, frequency
of record use, value of the records, etc. See

ANSI/PIMA IT9.11-1993

5

and ANSI IT9.2-1991.

Fire Protection

All Kodak Microfilms are slow-burning films as
defined by the American National Standards

Institute, Inc.
will burn considerably slower than paper, the
same precautions against damage by fire
should be taken for them as for paper records
of comparable value.

Depending on the importance of the records,
fire protection provided can vary from the full
protection described on the following pages for
valuable records to that provided by ordinary
office storage.

3

Even though photographic records

6

For example, LE-100 indicates that
information can be retrieved for at least
100 years of storage. Silver-gelatin films
have an LE of 500; thermally processed
silver (TPS) have an LE of 100 years.

D-31 June 2002 3

Storage Vaults

The highest degree of protection for a large
number of records is afforded by a fireproof
storage vault or record room. It should be located
and constructed in accordance with the local
building code, Fire Underwriters ’ Regulations, and
the requirements of the National Fire Protection
Association (NFPA)
room, except that an approved, controlled,
air-conditioning unit shoul d be installed. While
NFPA discourages air conditioning such an
installation, the fire hazard introduced by
openings for air-conditioning ducts can be
overcome by the use of automatic, fire-control
dampers approved by Underwriters’ Laborato ries,
Inc. These can be installed in the ducts in
accordance with recommendations of NFPA.
Sufficient insulati on should be provided in the
vault to permit satisfactory temperature control at
all seasons of the year and to prevent moisture
condensation from forming on the walls.

7

for a valuable record

8

moisture, which will expand under heat and, under
some conditions, might generate slight press ure.
However , such intense heat would be requi red on
the outside of the fire-resistant cabinet that the
cabinet would be seriously damaged from the fire
before appreciable pressure developed.

Effects of High Temperatures

In addition to complete l oss by fire , damage to film
records can also oc cur i f the y ar e exposed t o v ery
high temperatures. Excessive heat causes fil m to
buckle because of shrinkage at the edges. When
severe, this distortion affects the ease with which
the information can be taken from microfilms,
either by projection (for reading) or by printing
onto another film.

Silver-gelatin films that have been conditioned at
a relative humidity of 50% or lower will withstand
121°C (250°F) for 24 hours without significant
loss in readability or printability. At 149°C (300°F),
severe distortion can occur in a few hours.

Cabinets and Safes

For smaller quantities of records , a fi re-resistant
cabinet or safe of the type described by NFPA

will provide considerable protection. Such a safe
should protect records against a severe fire for at
least four hours.

Many fire-resistant safes and cabi nets use a type
of insulation that when heated releases moisture
and thus fills the interior of the safe with steam
during a fire. This can cause melting or stripping
of the film emulsion layer and loss of the image.
For protection, films stored in such a safe should
be placed in moisture-tight cans, as descri bed
under “Humidity Control” in this publ ication.

It is preferable to use fire-resi stant safes that are
available with an inner chamber sealed against
moisture. These are classified by Underwriters’
Laboratories, Inc., as Class 150 Record

Containers.

9

Film damage caused by steam

is not a problem with these safes.
The question is sometimes raised as to whether

microfilm stored in drawers or cabinets designed
to resist fire for several hours might, in case of a
fire, generate enough pressure to damage or
explode the cabinet. There is practically no
danger of an explosion from the storage of either
Estar Base or acetate base safety film under
these conditions. There are small amounts of
organic materials in acetate film base, as well as

7

Films that have been conditioned at a relative
humidity above 50% may show objectionable
distortion in somewhat shorter times or at lower
temperatures. Higher humidities, however , are
undesirable for other reasons, as explained later.

Thermally processed silver films will build
up background densities fairly rapidly at
temperatures of 93°C (200°F) and above.
At these temperatures, even a few hours will
produce significant loss in readability or
printability. At 149°C (300°F) or above, severe
distortion can occur in a few hours.

Diazo films, while quite stable, cont ain dye images
that can fade and/or discolor as a result of high
temperatures. Kodak Diazo Microfilms can
withstand a week at 93°C (200°F) without image
loss. At 149°C (300°F) or above, severe distor tion
can occur in a few hours.

High temperature is the greatest enemy of
vesicular film. Although Kodak Thermal Print
Films can withstand 71°C (160°F) for several
hours, high temperatures can cause a complete
loss of images if care is not taken with regard to
temperature control.

4 D-31 June 2002