- Preservation of magnetic audiotape
There are multiple types of
magnetic media, however this article focuses on recommended best practices for handling, cleaning and storage of magnetic audiotapes in an archival repository, either in the form of open reels or enclosed cassettes. Although digitizationof materials on fragile magnetic media in library and information scienceis a common practice, this article focuses on conserving the actual physical magnetic tape and playback equipment as artifacts, as there is still a need for this.
Recordists began recording sound on magnetic media in the late forties in the form of magnetic wire and tape recordings. Wire provided higher quality sound; however, tape was sturdier, and thus became the magnetic medium of choice. The tape consists of a coating of
iron oxide(Fe2O3) powder on a long strip of paper, acetate or polyester. Polyester is used in modern tapes; however, early tapes were made on paper, and then acetate bases, which were both prone to damage and chemically-unstable. Although the polyester tape is much more stable than the acidic paper tape or the volatile acetate tape, it is not perfect. In the late 1970s polyester tapes suffered a manufacturing defect which caused a problem known as “sticky-shed”. The tape sticks together because of a breakdown in the polyurethanebinder that holds the iron oxide atoms to the tape, [ Vidipax, (2001). Magnetic Tape Preservation: Problems with Magnetic Tape. Retrieved April 9, 2007, from Vidipax Web site: [http://www.vidipax.com/magtapeprobs.php] ] and must be baked at a very low temperature in order to be played. [ Hall, Stephanie A. “Preserving Sound Recordings”. Save Our Sounds: America’s Recorded Sound Heritage Project. 27 April, 2005 [http://www.loc.gov/folklife/sos/preserve1.html] ,9 April, 2007.] This breakdown is caused by hydrolysis, where water molecules break the long polyester links found in the polyurethane base [ Vidipax, (2001). Magnetic Tape Preservation: Problems with Magnetic Tape. Retrieved April 9, 2007, from Vidipax Web site: [http://www.vidipax.com/magtapeprobs.php] ] . The tape becomes sticky and will not only bond to itself, but will also leave deposits on the tape head in the playback equipment, which will cause frictionand eventually prohibit playback.
It is advised that open reels are handled by the center hub area or by the outer edges of the reel flanges, if necessary, and that the actual tape is not touched. If the outer flanges must be used, do not squeeze the edges of the reel flanges together, as it will damage the edges of the tape. If possible, handle by the center hub only. [(1997, October 29). Preservation of Recorded Sound Materials. Retrieved April 9, 2007, from Music Division: National Library of Canada Web site: [http://www.collectionscanada.ca/6/28/s28-1019-e.html#a11] ] Similarly, it is recommended that cassettes be handled by the existing outer plastic case and that fingers not be placed anywhere inside the cassette mechanism. [ Library of Congress, (2006, December 11). Cylinder, Disc, and Tape care in a nutshell. Retrieved April 9, 2007, from The Library of Congress: Preservation Web site: [http://www.loc.gov/preserv/care/record.html] ]
If tapes are dropped during handling, the shock from the drop can rearrange the ferromagnetic particles, which will have an ill effect on the high frequencies in the recording concerned. [ (1997, October 29). Preservation of Recorded Sound Materials. Retrieved April 9, 2007, from Music Division: National Library of Canada Web site: [http://www.collectionscanada.ca/6/28/s28-1019-e.html#a11] ]
Magnetic tape must be kept clean in order to prevent scratching and deterioration. Dust on the surface of tape traps moisture and will eventually precipitate hydrolysis. Also, dust deposits will cause friction between the tape and the tape heads on the playback equipment, which will scratch the
oxidelayer. The website for sound preservation hosted by the national Library of Canada classifies dirt in two classes: Foreign matter (fingerprints, dust) and alteration of the original state (chemical reactions caused due to grime and dirt deposited on the tape surface). [ (1997, October 29). Preservation of Recorded Sound Materials. Retrieved April 9, 2007, from Music Division: National Library of Canada Web site: [http://www.collectionscanada.ca/6/28/s28-1019-e.html#a11] ] In any event, the tapes must be properly cleaned.
Recommended methods for removing dust on tapes include using a small vacuum with a hose or wipe with 3M Tape Cleaning Fabric. One must be very careful when using a vacuum if a hose attachment is available. If the motor of the vacuum is powerful enough, it can demagnetize the tape and the recording will be compromised. Many of the professional companies for tape restoration recommend professional help for proper care, naturally, as they want business. They are generally correct to recommend this, as it is a delicate process that requires training if one plans to undertake serious chemical or physical repair. Vidipax, a professional tape restoration company, recommends using Pellon fabric or cloth as the safest and most efficient way to clean tapes. They warn again using solvents at all costs unless the tapes have already been submerged in water or another solvent (in the case of a flood). They also remind tape-owners or collections managers that baking tapes to reverse hydrolysis is rarely a permanent fix and permanently alters the make-up of the tape. [Vidipax, (2007). Magnetic Tape Restoration. Retrieved August 02, 2008, from the Vidipax Web site: [http://www.vidipax.com/magtaperest.php] ]
As is the case with any collection, proper storage is extremely important. The general environment, including temperature and relative humidity is key. The proper levels vary depending on how long the materials need to be stored. The Library of Congress [ Library of Congress, (2006, December 11). Cylinder, Disc, and Tape care in a nutshell. Retrieved April 9, 2007, from The Library of Congress: Preservation Web site: [http://www.loc.gov/preserv/care/record.html] ] recommends that any tapes needing preservation for a minimum of 10 years should be stored between 65-70 degrees
Fahrenheitat 45-50% relative humidity(RH). Large fluctuations in either of these factors should be avoided at all costs. If the tapes need permanent preservation, they should be stored at 46-50 degrees Fahrenheit at 20-30% relative humidity. In the case of magnetic tapes, contrary to traditional preservation storage rules for books and photographic film, colder is certainly not better. If the collections are stored below 46 degrees F, the tape lubricantcan separate from the base, ruining the recording. The most important thing is to keep conditions consistent once desirable conditions are achieved.
The National Library of Canada recommends that one and a half rounds of a previously-unused tape should be cut off, so as to remove any adhesive at the end, which could later be transferred to the tape or machinery. They also recommend not storing any paper labels in the box with reel-to-reel tapes to prevent chemical transfer from the paper and/or printing processes used on the paper to the tape. [ (1997, October 29). Preservation of Recorded Sound Materials. Retrieved April 9, 2007, from Music Division: National Library of Canada Web site: [http://www.collectionscanada.ca/6/28/s28-1019-e.html#a11] ]
The Library of Congress recommends that tapes with water repellent plastic containers be stored vertically on edge, not flat, and that reel-to-reel boxes need not be separated, but should be stored vertically with bookends, so as not to fall. Also, it is always important to remember that these collections will be very heavy and should be shelved on strong, non-acidic shelving.
Tapes should only be rewound just before the next play. When rewinding, if possible, use a slower archival wind technique. Although super-speed rewinders may seem convenient, they will warp and damage tapes over time. Professional media librarians at the National Library of Canada suggest that the best way to achieve an archival wind for reel-to-reel tapes is to remove the heads on the player and play backwards at normal play speed. However, the tape tension may need to be adjusted after removing the heads.
Sometimes, a tape may be so fragile that the only long-term method for preservation is to transfer the media to a digital format. However, all of the above precautions still must be taken with collections in order to get a proper transfer. The materials must be in good enough condition to play in order to be digitized; therefore, one should not count on digitization as a safety net.
Additional Sources Consulted:
* Stauderman, Sarah, [http://www.arl.org/preserv/sound_savings_proceedings/Pictorial_guide.shtml "Pictoral Guide to Sound Recording Media"] , Preservation: Sound Savings, preserving Audio Collections. Association of Research Libraries.
Preservation (library and archival science)
Tape baking- an unintuitive preservation technique.
Magnetic tape sound recording
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