Magnetic tape deterioration

We are about to commence a cooperative research project between the
National Library of Australia and the National Film and Sound Archive to
investigate the deterioration of magnetic tape.

In our Oral History collection we have a large number of magnetic
reel-to-reel tapes that are exhibiting symptoms of the so-called
'hydrolysis' problem.  When tapes suffering from this problem are played
the sound is distorted, a high pitched squeal is emitted and the player
eventually jams because the tape has exuded gummy degradation products.
'Baking' the tapes in a warm, dry oven is known to make most tapes
playable, however, this has not always worked on all tapes we have tried
to restore, and we are concerned that the baking process may result in
the distortion of the sound.  (All the research reports we have located
deal with digital tape--all our tapes are analogue.)

We intend to undertake a number of relatively simple projects to
investigate what is occurring during the degradation and baking
processes, and to determine if there is a less severe means of restoring
the tapes to a playable condition without the loss of sound quality.
These projects include storing tapes for 1-2 years in low permeability
bags with a desiccant to determine if this is an effective way of making
the tapes playable; determining the moisture content of reels of tapes
and investigating how this changes during the degradation and baking
processes; to determine if replaying tapes in a low humidity environment
will enable them to be played without squeal or jamming; and to
determine whether it is the increased temperature or reduced humidity
that is effective in restoring tapes during the baking process.

We hope that the results of these investigations will help us to arrive
at a suitable treatment program for our tapes.

We are keen to hear from anyone who may have done similar
investigations, know of any such investigations, or be interested in
sharing any ideas on the topic.

Thanks,

Leanne Brandis, Chemist, Preservation Services
Jan Lyall, Director, National Preservation Office
National Library of Australia
Phone: +616 262 1571
Fax: +616 257 1703

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                  Conservation DistList Instance 7:43
                Distributed: Thursday, December 9, 1993
                        Message Id: cdl-7-43-004
                                  ***