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From: bcollins@axion.bt.co.uk (bill collins)
Newsgroups: sci.electronics
Subject: Re: What is the life-time of magnetic tape?????
Message-ID: <1991Feb4.100546@axion.bt.co.uk>
Date: 4 Feb 91 10:05:46 GMT
Sender: news@axion.bt.co.uk
Reply-To: bcollins@axion.bt.co.uk (bill collins)
Organization: British Telecom Research Labs
Lines: 44


I recently read an old copy of "New Scientist" (22 Sep 90), which talked
about the problems facing master audio tapes, although I guess that there
could be related problems to computer tapes ...

The article mentions, in particular, the use of polyurethane as a binder
on tapes (the "glue" that holds the magnetic iron oxide onto the polyester
film base). The polyurethane absorbs water, and releases an acid which 
produces gummy residues on the tape. The tape then sticks and judders in 
the tape recorder.

Apparently, this is a problem mainly for tapes produced between the
mid-70's and mid 80's (although this binder was used as early as 1962).
Problems have been found recently with studio quality tapes of that era,
but could affect any tape produced in that period. Ampex are named as
one make which is known to suffer from this problem (quarter and 2 inch
tapes); whilst Agfa are reported as having had problems only 3 years ago,
after a change of chemical mix.

There is a way of stabilising affected tapes (baking them in an oven
for up to 6 days at temperatures up to 50 C.), which will allow them to
be transferred onto more stable stock. However, this is not a trivial
problem .... EMI's Abbey Road recording studios are reported to have
around 280,000 tapes in their archives !

I don't think that this proves very much, except that long-term storage
of any material is open to doubt (and may not be predictable). In the
main, you hope that you never need to go back into the archives.
"Use it or lose it" seems to be the appropriate motto here ...


Regards,
        Bill

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