The most detailed and authoritative advice available on the long term preservation of magnetic tape recordings can be found in Factors Relating to Long Term Storage of Magnetic Tape, published for limited circulation by EMI Ltd Central Research Laboratories in May 1976. This report is reprinted in full in the July 1977 issue of the Phonographic Bulletin (Number 18). Copies are available to members of the International Association of Sound Archives or by subscription and can be obtained through the Secretary of IASA.1 The advice given in this section summarises the main factors relating to tape preservation and is intended as a basic guide for institutions who may not be able to apply fully professional sound archive procedures.
(1) The Medium
The most important single safeguard against the deterioration of archive recordings is the use of an appropriate tape. Tape characteristics and brands suitable for preservation copies are dealt with in Chapter 10.
(2) The Environment
The recommended conditions for magnetic tape storage are those within the temperature range 7 to 13°C (approximately 45 to 55°F), with relative humidity between the limits 40 to 60% and a magnetic environment not in excess of 10 oersteds. Collecting centres without the use of fully control1ed storage facilities can nonetheless avoid clearly unsuitable locations. As a general guide tapes may be stored in areas in which there is a dry and comfortable working temperature that is not subject to variations of more than 10°C between its upper and lower limits. The area must not be adjacent to any strong magnetic fields (the most common sources of which are power cables and electrical distribution points) or have magnetic devices such as loudspeakers and microphones placed in the vicinity.
Before storage, tapes should be properly wound. Most good quality tape machines (see Chapter 9) will give the kind of firm -but not too tight -and even wind that is necessary to provide a smooth edge across the full length of the tape. This will avoid the possibility of any tape layers standing proud of their neighbours, which are particularly vulnerable to damage (see also Chapter 10).
(4) Tape Spools
Archive tapes should be stored on spools no less than 7" in diameter. Smaller spools have narrow hubs around which the tape is very tightly curved and consequent stress patterns at the centre of the reel can permanently deform the tape. The spool should also be strong with as little 'window' area in the flange as possible, so that it provides the tape with good physical support and protection.
(5) Tape Containers
If they are not made of metal or plastic material tape cartons should be of a sturdy cardboard construction with a low acid content. As an additional refinement hermetically sealed plastic bags give some protection against airborne dust particles.
(6) Checking and Testing
Routine rewinding (yearly or two yearly) of tapes may reduce print-through effects and is also useful for reversing the curvature -and thereby relieving the stress patterns -which is set up in tapes stored in one position over a long period of time. A periodic visual inspection should also be made to check that archive copies are not deteriorating in storage through warping or fungal attack. Only by playing the tape, however, can it be established whether any magnetic degradation has taken place or whether the results of any physical damage have affected the tape's replay characteristics. In such an eventuality the only remedial action that can be taken is to copy the recording onto new tape.
Few professional archives have the resources to apply the full range of recommended conservation practices. It may be that collecting centres with small tape collections can afford higher standards! A good archive tape, a stable storage environment and well wound tapes on suitable spools are standards which most collecting centres should be able to afford and which represent reasonable insurance for the long term safety of archive tapes.
- For membership and subscription details contact David Lance, Secretary lASA, Imperial War Museum, Lambeth Road, London SEI 6HZ, England.