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Micrographic Quality
D-31
Storage and
Preservation
of Microfilms
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Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Electronic Imaging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Record Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Storage Hazards and Protection . . . . . . . . . . . . . . . . . . . . . . .
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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 . . . . . . .
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Introduction Definitions Photographic film remains an important To help understand storage requirements, documentary material. The increasing quantity the composition and structure of microfilm are and value of microfilm records used in financial described and definitions of commonly used 1 institutions, libraries, government offices, and terms are given. industrial firms have focused attention on the care of such records to make certain that they last as long as possible. The distinctio
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Emulsion layer(s)—image or image-forming All silver-gelatin Kodak Microfilms on Estar Base, layer(s) of photographic films, papers, and plates. when processed as recommended by Kodak, meet the current specifications established by the Film base—the plastic support for the emulsion American National Standards Institute, Inc., and backing layers. (ANSI) for films intended for use as LE 500. Halation—halo or ghost around the desired Substratum (subbing or precoat)—the layer image on a photog
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Scanner—a device that electro-optically converts Extended-term storage conditions—storage a document into a series of pixels by detecting conditions suitable for the preservation of and measuring the intensity of light reflected or recorded information on the majority of freshly transmitted. When initially captured, each pixel is processed photographic films for 500 years. a level of brightness (gray or color), initially an Medium-term storage conditions—storage analog quantity, but potenti
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Storage Vaults moisture, which will expand under heat and, under some conditions, might generate slight pressure. The highest degree of protection for a large However, such intense heat would be required on number of records is afforded by a fireproof the outside of the fire-resistant cabinet that the storage vault or record room. It should be located cabinet would be seriously damaged from the fire and constructed in accordance with the local before appreciable pressure developed. buil
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High Humidity Water Protection Storage in moist air, such as that frequently found Film records should be protected from possible in basement rooms, and storage humidities above water damage, such as from leaks, fire-sprinkler 50% should be avoided; relative humidities of discharge, and flooding. If possible, storage 40% or less are recommended for minimizing the facilities should be located above basement possibility of growth of microscopic blemishes. levels. Storage cabinets should b
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Very low humidities have, in the past, caused film Molecular Sieves to be brittle. However, film of current manufacture Molecular sieves are capable of absorbing most has not been found to exhibit brittleness or of the potential film degradation agents such as breaking tendencies under normal handling, moisture, oxidants, solvents, and others when even at relative humidities as low as 15%. Old film kept in close proximity with the films under that is found to be brittle at low humidity
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Moisture-Tight Containers Humidity Control If humidity control of the storage area is not Control of relative humidity is required for possible, the storage of film in moisture-tight preservation of permanent records. containers is required to maintain the film’s Air Conditioning humidity limits. The film must be conditioned to the required humidity before being sealed in the Properly controlled air conditioning of the storage container. This requires the temporary use of an area is defi
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Humidification Microscopic Blemishes Humidification is not necessary or desirable Some processed silver-gelatin microfilms in unless the prevailing relative humidity is under storage for two to twenty years have developed 15%—under 30% for polyester-base films—for microscopically small colored spots or blemishes. long periods of time and unless the film is used The fogged leader at the outside of the roll is most frequently and physical troubles are encountered. frequently affected by t
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The conditions under which microfilm is stored Chemical Contamination have been found to play an important role in Air contaminants may add an oxidizing or the development of microscopic blemishes. reducing effect to the atmosphere. This in turn Storage in cool, dry air that is free of oxidizing may cause deterioration of the film base and a gases or vapors is an effective means for gradual fading of the photographic image, as arresting their formation and growth. Storage well as the f
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Adhesive Composition of Enclosure Materials Some photographic images can be damaged Paper by adhesives incorporating impurities such as sulfur, iron, copper, or other ingredients that Paper should be made from rag, bleached sulfite might react with image silver or gelatin. Pressure- or bleached kraft pulp with an alpha-cellulose sensitive adhesives and ether-linked products content greater than 87%. It should be free from should be avoided. highly lignified fibres, such as ground wood, as
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To make sure that there is enough time for the Processing for Permanence fixing reaction to be completed, specific recommendations for each type of film should Silver-Gelatin Films be followed. Undeveloped silver halides are Processing is one of the most important dissolved by the fixer as complex ions of silver factors affecting the potential permanence of and thiosulfate. As the silver content of the fixer photographic records. The removal of residual increases with processing, the si
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Residual Hypo Test Squeegees The accepted criterion for adequate washing is It is important to use an adequate squeegee the methylene blue method described in ANSI/ where the film leaves the water wash and enters 19 PIMA IT9.17-1998. IT9.17-1998 also describes the drying section. Otherwise, residual water the silver densitometric method, which has been droplets will dry and form visible surface defects suggested by the Association for Information and and, in some cases, cause physical s
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Processing of Other Film Types Special Storage and Hazards Thermally Processed Silver (TPS) Underground Storage This film should be processed in accordance Most large industrial organizations and with the manufacturers’ recommendations for government agencies have developed methods optimum image stability. ANSI/PIMA IT9.19-1994 for safeguarding vital records in the event of a war 24 or a natural catastrophe. Many keep their vital and ISO-18919-1999 give specifications for records in undergr
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Time-Capsule Storage Interfiling Only silver-gelatin films conforming to ANSI/PIMA Microfilm may be subject to interactions when 2 stored with films of different generic types IT9.1-1998 or ISO 18901-1999 should be used (e.g., diazo and silver-gelatin). Do not wind for time capsules or sealed in cornerstones of different generic film types on the same roll or buildings. Film intended for this kind of storage store them in the same container. Diazo and should be conditioned to a low relat
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Sometimes film inspection is considered too Inspection laborious and costly and is neglected for many The potential life of photographic records depends years—occasionally with unfortunate results. largely on atmospheric conditions—temperature, If it is not always possible to open every film humidity, cleanliness—and the manner in which can or rewind every roll at the recommended the film is used. If storage conditions are kept frequency, select a few rolls at random from within the li
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Table 2: Storage Life of Microfilms Anticipated Storage Life Film/Type/Parameter Medium Term Extended Term Long Term (Minimum of 10 Years) (Minimum of 100 Years) (Indefinitely) Silver-Gelatin Films Not above 0.030 grams Not above 0.014 grams (1), (2) per square meter (1) per square meter (1) Residual Hypo No more than perceptible tint by spot stain test. — Residual Silver Salts All Films— Storage Conditions See Table 3 Temperature and Relative Humidity Air Conditioning Not necessary Essential
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Although the same general storage principles Summary of Requirements for apply to medium-term and long-term storage Storage and Preservation of records, much greater care must be taken to obtain maximum protection for long-term storage Records on Kodak Microfilm records; makeshift or temporary arrangements should not be considered. Storage Facilities In summary, Table 3 indicates the conditions that The type of storage vault, safe, cabinet, or area are considered suitable for black-and-
