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

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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

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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

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.

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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).

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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

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.

Even though photographic records

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.

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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.

for a valuable record

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.

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

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.

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