Preservation of magnetic audiotape
Encyclopedia
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 digitization of materials on fragile magnetic media in library and information science
is 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.
in terms of sturdiness and the ability to edit by cutting and splicing made tape preferable to wire as the magnetic medium of choice. Tape consists of a coating of a magnetic pigment, typically iron oxide
(Fe2O3
), on a long strip of polyester (polyethelyne terephthalate) base film. This base film has been used since the mid-sixties as a replacement for acetate bases
film that was prone to chemical instability. Chemical instability reared its head again in the mid-seventies when two significant tape manufacturers changed their dispersion formulations by introducing a polyurethane binder that, in time, turned hydroscopic and broke down as it absorbed water molecules into the long hydro-carbon molecular chains. The tape coatings became sticky and shed oxide onto all tape recorder parts in their path, including heads, guides, rollers, and capstans. This is commonly called sticky-shed syndrome
. Although the problem was confined to two of the four major tape manufacturers (neither BASF nor 3M studio tapes suffer from the problem because neither manufacturer used the hydroscopic binder), all magnetic tapes have been tainted by the defect. Information can be recovered from the "stick-shed" tapes by heating them at a very low temperature in order drive the water out of the binders. The baking method is a one-time solution to the problem because the binder remains unstable. Tapes that do not show the breakdown syndrome do not need any special treatment.
be handled by the existing outer plastic case and that fingers not be placed anywhere inside the cassette mechanism.
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). 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 against 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.
at 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 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 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.
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.
Archive
An archive is a collection of historical records, or the physical place they are located. Archives contain primary source documents that have accumulated over the course of an individual or organization's lifetime, and are kept to show the function of an organization...
, either in the form of open reels or enclosed cassettes. Although digitization of materials on fragile magnetic media in library and information science
Library and information science
Library and information science is a merging of the two fields library science and information science...
is a common practice, this article focuses on conserving the actual physical magnetic tape and playback equipment as artifacts
Cultural artifact
A cultural artifact is a term used in the social sciences, particularly anthropology, ethnology, and sociology for anything created by humans which gives information about the culture of its creator and users...
, as there is still a need for this.
Basics
The first magnetic tapes were manufactured by BASF in Germany in 1932. These were designed with iron carbonyl as the magnetic pigment mixed into the cellulose acetate carrier. Production soon moved to iron oxide coated onto cellulose acetate rolls cut into uniform strips wound onto plastic or metal hubs. Recordists began recording sound on magnetic media in the twenties in the form of magnetic wire. After World War II, the advantages of tapeMagnetic tape
Magnetic tape is a medium for magnetic recording, made of a thin magnetizable coating on a long, narrow strip of plastic. It was developed in Germany, based on magnetic wire recording. Devices that record and play back audio and video using magnetic tape are tape recorders and video tape recorders...
in terms of sturdiness and the ability to edit by cutting and splicing made tape preferable to wire as the magnetic medium of choice. Tape consists of a coating of a magnetic pigment, typically iron oxide
Iron oxide
Iron oxides are chemical compounds composed of iron and oxygen. All together, there are sixteen known iron oxides and oxyhydroxides.Iron oxides and oxide-hydroxides are widespread in nature, play an important role in many geological and biological processes, and are widely utilized by humans, e.g.,...
(Fe2O3
Iron(III) oxide
Iron oxide or ferric oxide is the inorganic compound with the formula Fe2O3. It is one of the three main oxides of iron, the other two being iron oxide , which is rare, and iron oxide , which also occurs naturally as the mineral magnetite. As the mineral known as hematite, Fe2O3 is the main...
), on a long strip of polyester (polyethelyne terephthalate) base film. This base film has been used since the mid-sixties as a replacement for acetate bases
Base (chemistry)
For the term in genetics, see base A base in chemistry is a substance that can accept hydrogen ions or more generally, donate electron pairs. A soluble base is referred to as an alkali if it contains and releases hydroxide ions quantitatively...
film that was prone to chemical instability. Chemical instability reared its head again in the mid-seventies when two significant tape manufacturers changed their dispersion formulations by introducing a polyurethane binder that, in time, turned hydroscopic and broke down as it absorbed water molecules into the long hydro-carbon molecular chains. The tape coatings became sticky and shed oxide onto all tape recorder parts in their path, including heads, guides, rollers, and capstans. This is commonly called sticky-shed syndrome
Sticky-shed syndrome
Sticky-shed syndrome is a condition created by the deterioration of the binders in a magnetic tape, which hold the iron oxide magnetizable coating to its plastic carrier. This deterioration renders the tape unusable...
. Although the problem was confined to two of the four major tape manufacturers (neither BASF nor 3M studio tapes suffer from the problem because neither manufacturer used the hydroscopic binder), all magnetic tapes have been tainted by the defect. Information can be recovered from the "stick-shed" tapes by heating them at a very low temperature in order drive the water out of the binders. The baking method is a one-time solution to the problem because the binder remains unstable. Tapes that do not show the breakdown syndrome do not need any special treatment.
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. Similarly, it is recommended that cassettesCompact Cassette
The Compact Cassette, often referred to as audio cassette, cassette tape, cassette, or simply tape, is a magnetic tape sound recording format. It was designed originally for dictation, but improvements in fidelity led the Compact Cassette to supplant the Stereo 8-track cartridge and reel-to-reel...
be handled by the existing outer plastic case and that fingers not be placed anywhere inside the cassette mechanism.
Cleaning
Magnetic tape must be kept clean in order to prevent scratching and deterioration. Dust on the surface of tape will cause friction between the tape and the tape heads on the playback equipment, which will scratch the oxideOxide
An oxide is a chemical compound that contains at least one oxygen atom in its chemical formula. Metal oxides typically contain an anion of oxygen in the oxidation state of −2....
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). 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 against 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.
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 the materials need to be stored. The Library of Congress recommends that any tapes needing preservation for a minimum of 10 years should be stored between 65-70 degrees FahrenheitFahrenheit
Fahrenheit is the temperature scale proposed in 1724 by, and named after, the German physicist Daniel Gabriel Fahrenheit . Within this scale, the freezing of water into ice is defined at 32 degrees, while the boiling point of water is defined to be 212 degrees...
at 45-50% relative humidity
Relative humidity
Relative humidity is a term used to describe the amount of water vapor in a mixture of air and water vapor. It is defined as the partial pressure of water vapor in the air-water mixture, given as a percentage of the saturated vapor pressure under those conditions...
(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 lubricant
Lubricant
A lubricant is a substance introduced to reduce friction between moving surfaces. It may also have the function of transporting foreign particles and of distributing heat...
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 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.
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.
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 be digitized; therefore, one should not count on digitization as a safety net.See also
- Preservation (library and archival science)Preservation (library and archival science)Preservation is a branch of library and information science concerned with maintaining or restoring access to artifacts, documents and records through the study, diagnosis, treatment and prevention of decay and damage....
- Tape bakingTape bakingTape baking is a process that is used to restore magnetic tapes: audio cassettes and video tapes that have begun to go through a chemical breakdown due to age, known informally as shedding...
- an unintuitive preservation technique. - Magnetic tape sound recordingMagnetic tape sound recordingThe use of magnetic tape for sound recording originated around 1930. Magnetizable tape revolutionized both the radio broadcast and music recording industries. It did this by giving artists and producers the power to record and re-record audio with minimal loss in quality as well as edit and...