Preservation of magnetic audiotape

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There are multiple manifestations 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 there has been a great deal of digitization of materials on fragile magnetic media, this article does not address those practices, useful as they may be, but focuses rather on conserving the actual physical magnetic tape and playback equipment, as there is still a need for this.

Contents

[edit] Basics

Recordists began using magnetic recordings 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 iron oxide on a paper, acetate or polyester. Polyester is used in modern tapes, however, early tapes were made on paper, and then acetate bases, which were both problematic and 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 1970’s polyester tapes suffered a manufacturing defect which caused a problem known as “sticky-shed”. The tapes stick together and must be baked at a very low temperature in order to be played. [1] The science behind the sticky-shed syndrome basically involves a process called hydrolysis, where water molecules break the long polyester links found in the polyurethane base. [2] 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 friction and eventually prohibit playback. For more in depth information about the chemical processes involved in magnetic tape deterioration, visit this link on the Vidipax website. Vididpax is located in Long Island City, Queens, New York, and provides professional magnetic media preservation and transfer. Their website contains very detailed information.

[edit] Handling

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. [3] 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.[4]

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. [5]

[edit] Cleaning

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 oxide layer. 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). [6] 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 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 does, however, list some recommendations on their “Magnetic Tape Restoration” page. They recommend 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 hydrolusis is rarely a permanent fix and permanently alters the make-up of the tape.

[edit] Storage

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 you would like to store the materials. The Library of Congress [7] recommends that any tapes needing preservation for a minimum of 10 years should be stored between 65-70 degrees F at 45-50% relative humidity (RH). Large fluxuations 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 F at 20-30% RH. In the case of magnetic tapes, colder is certainly not better. If the collections are stored below 46 degrees F, the lubricant can 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 “virgin” 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. The website does not indicate exactly why this is. [8]

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.

As for winding, the tape should be played through and then stored. The tape should only be rewound just before the next play. Also, when this is done, if possible, use an archival wind, which basically implies SLOW. Although super-speed rewinders may seem convenient they will warp and damage tapes over time. It has been recommend by professional media librarians at the National Library of Canada 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.

One final comment on digitization: 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 transfer, therefore, one should not count on digitization as a safety net.

[edit] References

  1. ^ Hall, Stephanie A. “Preserving Sound Recordings”. Save Our Sounds: America’s Recorded Sound Heritage Project. 27 April, 2005 [1],9 April, 2007.
  2. ^ Vidipax, (2001). Magnetic Tape Preservation: Problems with Magnetic Tape. Retrieved April 9, 2007, from Vidipax Web site: [2]
  3. ^ (1997, October 29). Preservation of Recorded Sound Materials. Retrieved April 9, 2007, from Music Division: National Library of Canada Web site: [3]
  4. ^ 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: [4]
  5. ^ (1997, October 29). Preservation of Recorded Sound Materials. Retrieved April 9, 2007, from Music Division: National Library of Canada Web site: [5]
  6. ^ (1997, October 29). Preservation of Recorded Sound Materials. Retrieved April 9, 2007, from Music Division: National Library of Canada Web site: [6]
  7. ^ 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: [7]
  8. ^ (1997, October 29). Preservation of Recorded Sound Materials. Retrieved April 9, 2007, from Music Division: National Library of Canada Web site: [8]

Additional Sources Consulted:

[edit] See also