Re: [AV Media Matters] Digitizing Audio and Video-Mediarecoverability

[rohre@ARLUT.UTEXAS.EDU]

Jim,
I think you are correct about the back coating and sticky shed.   Our
recent
study of several tapes revealed most of the deposit is on the back
guides,
not the heads which touch the oxide surface.  We had a sapphire back of
the
tape fixed guide that was most affected, because it was the first thing
the
tape encounters coming off the supply reel.

It is of course possible that a drive that did not, in effect, scrape
the
back of the tape would be less affected; but also in our experience, a
few
years ago with such a drive, it only resulted in clogging the heads
themselves and "welding" the tape to them.   It caused failure of the
servo
power transistors attempting to make the motor pull the tape that was
sticking.

A contributing factor to shedding problems can be deep wear patterns in
heads, fixed, or other guides which can leave sharp shoulders to abrade
the
tape edge.

It is said the fingernail can detect a wear pattern of 0.001 inch deep
as
just detectable.
Even that little seems to be a factor with shedding tapes.

One of the problems of dealing with old tapes is that the machines to be
used often have wear issues.  A close inspection before use on
reconditioned
tapes is indicated.

Heads can develop wear patterns that also provide a shoulder which can
cause
a tape to jump the track at higher speeds.

One must never forget the recorder and media are a system which all must
be
in good condition for good results.

The good news is with reconditioned elastomer capstans and replaced
guides
and careful baking cycles,  time for the molecules to realign after the
humidity is driven out of the urethane, the old tapes  can be played.
I
would not suggest waiting 28 years, before reclaiming the data, but 10
years
seems to be a completely recoverable storage for back coated tape, if
you do
one baking cycle before play.

Jim Wheeler points out that he has baked some tapes multiple times over
a
time period, and they recover; thus, one has some assurance of getting
the
data back.  In my own past experience with shedding and baking, I have
seen
a tape that was even shedding oxide from the mylar surface to bare film;
be
baked, and able to play back normally enough times to retrieve the data
to
another format.
-Stuart Rohre
Applied Research Labs

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