Micrographic Quality D-31 Storage and Preservation of Microfilms
Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Electronic Imaging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Record Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Storage Hazards and Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Processing of Other Film Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . Thermally Processed Silver (TPS) . . . . . . . . . . . . . . . . . . . . . . . . Diazo Films . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Vesicular Films . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Special Storage and Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Underground Storage . . . . . . . . . . . . . . . . . . . . . . .
Introduction Definitions Photographic film remains an important documentary material. The increasing quantity and value of microfilm records used in financial institutions, libraries, government offices, and industrial firms have focused attention on the care of such records to make certain that they last as long as possible. To help understand storage requirements, the composition and structure of microfilm are described and definitions of commonly used terms are given.
Emulsion layer(s)—image or image-forming layer(s) of photographic films, papers, and plates. Film base—the plastic support for the emulsion 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 from the 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.
Scanner—a device that electro-optically converts 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. Extended-term storage conditions—storage conditions suitable for the preservation of recorded information on the majority of freshly processed photographic films for 500 years.
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)7 for a valuable record room, except that an approved, controlled, air-conditioning unit should be installed.
Water Protection High Humidity Film records should be protected from possible water damage, such as from leaks, fire-sprinkler discharge, and flooding. If possible, storage facilities should be located above basement levels. Storage cabinets should be raised so that the lowest shelf or drawer is at least 15.2 cm (6 in.) off the floor and should be constructed so that water cannot splash through ventilating louvers onto the records.
Very low humidities have, in the past, caused film to be brittle. However, film of current manufacture has not been found to exhibit brittleness or breaking tendencies under normal handling, even at relative humidities as low as 15%. Old film that is found to be brittle at low humidity should be reconditioned to a higher humidity before use.
Humidity Control Moisture-Tight Containers Control of relative humidity is required for preservation of permanent records. If humidity control of the storage area is not possible, the storage of film in moisture-tight containers is required to maintain the film’s humidity limits. The film must be conditioned to the required humidity before being sealed in the container. This requires the temporary use of an air-conditioned cabinet or room, or an electrical dehumidifier.
Humidification Microscopic Blemishes 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.
The conditions under which microfilm is stored have been found to play an important role in the development of microscopic blemishes. Storage in cool, dry air that is free of oxidizing gases or vapors is an effective means for arresting their formation and growth. Storage in sealed, metal cans is a sound preventive measure, if this is practical and consistent with the humidity requirements.
Composition of Enclosure Materials Paper Paper should be made from rag, bleached sulfite or bleached kraft pulp with an alpha-cellulose content greater than 87%. It should be free from highly lignified fibres, such as ground wood, as determined by the phloroglucinol spot test. For paper in direct contact with black-and-white photographic material, the pH should be between 7.5 and 9.5. The pH should be close to 7.0 when in direct contact with color or diazo material.
Processing for Permanence Silver-Gelatin Films Processing is one of the most important factors affecting the potential permanence of photographic records. The removal of residual processing chemicals, the exclusion of dirt contamination, and uniform drying are factors normally controlled by proper processing. Processed film, for long-term storage or permanent records, must meet the requirements of ANSI/PIMA IT9.1-1992 (R1996) or ISO 18901.
Squeegees Residual Hypo Test It is important to use an adequate squeegee where the film leaves the water wash and enters the drying section. Otherwise, residual water droplets will dry and form visible surface defects and, in some cases, cause physical sticking of the film laps. In wound-up rolls, these spots may provide places where microscopic blemishes can form. Inspect squeegees regularly (particularly blade and roller types) to make sure that they do not cause film scratches.
Processing of Other Film Types Special Storage and Hazards Thermally Processed Silver (TPS) Underground Storage This film should be processed in accordance with the manufacturers’ recommendations for optimum image stability. ANSI/PIMA IT9.19-1994 and ISO-18919-199924 give specifications for stability of TPS films. Most large industrial organizations and government agencies have developed methods for safeguarding vital records in the event of a war or a natural catastrophe.
Time-Capsule Storage Interfiling Only silver-gelatin films conforming to ANSI/PIMA IT9.1-19982 or ISO 18901-1999 should be used for time capsules or sealed in cornerstones of buildings. Film intended for this kind of storage should be conditioned to a low relative humidity (20-30% is recommended for acetate-base films) in a conditioning room or chamber. During conditioning, air should be circulated against both roll surfaces.
Inspection The potential life of photographic records depends largely on atmospheric conditions—temperature, humidity, cleanliness—and the manner in which the film is used. If storage conditions are kept within the limits suggested in Table 3, inspection of an adequate number of properly selected lot samples should be made at two-year intervals.
Table 2: Storage Life of Microfilms Anticipated Storage Life Film/Type/Parameter Medium Term Extended Term (Minimum of 10 Years) (Minimum of 100 Years) Silver-Gelatin Films Residual Hypo (1), (2) — Residual Silver Salts All Films— Storage Conditions Temperature and Relative Humidity Not above 0.030 grams per square meter (1) Long Term (Indefinitely) Not above 0.014 grams per square meter (1) No more than perceptible tint by spot stain test.
Summary of Requirements for Storage and Preservation of Records on Kodak Microfilm Although the same general storage principles apply to medium-term and long-term storage records, much greater care must be taken to obtain maximum protection for long-term storage records; makeshift or temporary arrangements should not be considered. Storage Facilities The type of storage vault, safe, cabinet, or area selected must be based on the value of the film records and their intended storage life.
References and Bibliography 1. American National Standard: “Technical Report— Glossary of Document Technologies,” ANSI/AIIM TR2-1998. 2. American National Standard: “Imaging Materials— Processed Silver-Gelatin Type Black and White Film—Specifications for Stability,” ANSI/PIMAIT9.11996 or ISO 18901. 3. American National Standard: “Imaging Materials— Photographic Films - Specifications for Safety Film,” ANSI IT9.6-1991 (R1996) or ISO 18906. 4.
EASTMAN KODAK COMPANY Document Imaging Rochester, New York 14650 www.kodak.com/go/docimaging Kodak, Eastman, Estar, and Prostar are trademarks of Eastman Kodak Company. KODAK Publication No. D-31 CAT No. 811-6386 6/2002 © Eastman Kodak Company, 2002 Printed in U.S.A.
