Re: [AV Media Matters] Tape baking

[rohre@ARLUT.UTEXAS.EDU]

Group,
As a practical matter, the exit ports for cables and instrumentation wires
allows escape of the water vapor when baking in the scientific
environmental
chambers we use of the Blue M and similar brands.  The baking
time would seem
to be a matter of how long it takes to repolymerize the binder
and drive the
water out from the molecules.

At the moderate Ampex temperatures suggested, I have baked both
at the minimum
time and longer when I was not sure we were holding the temperature as
constant.  (That time we used a photo drying chamber in our photo
lab, and the
problem was its controller had quite an overshoot in temperature
each time the
heater came on.  Also, its circulation seemed to be less constant than the
larger industrial chamber I used for larger reel to reel tapes.)  However,
results were good from both methods, and the month or longer
lifetime for the
baked tape was confirmed.

Because we convert the tape to another media, or copy the tape
soon after the
stabilization period after baking; I have not rigorously explored the
condition of the baked masters after 30 days.  Incidentally, it is very
important to allow the tape to rest after baking for the full
amount of time.
Heat is retained inside the pack, especially in metal reels which
also heat
up, and the full 48 hours is used to allow the stresses in the
tape pack and
the heat to stabilize and come down.  Only then do we run the tape.

Tape is an amazing, forgiving, media.  We have seen edge abused
tapes allowed
to "rest" off a reel (in a deep box), and then repacked on a
reel, (thus self
"ironing",) recover to near perfect playback.  I have become
something of an
specialist here in successfully recovering in playable condition, cassette
tapes which for a variety of reasons are damaged, and the end
portion does not
retract into the cassette or gets tangled in R-DAT/4mm or 8mm or even VHS
drives.

One sure way to cause a cassette problems is to place labels in
other than the
recessed areas provided, or to sloppily apply a label, such that its edge
comes out of the recess.  Just fixed a VHS-C tape of high
interest that had
suffered this yesterday.  Usually, if you can work the tape
cassette out of
the transport enough to access the elevator platform, you can use
Q tips, or
other non magnetic wands to lift tape off rollers and drum and out of the
transport.  The most difficult tangled tape recovery efforts are
the 4mm and
8mm drives.  There, you must bite the bullet and remove the drive from its
case and access the top of the transport by removing the cover;
since the tape
is dragged behind the head drum in the loading process.  It is in the long
loop of tape that is pulled out in the load sequence that most
tangled tape
episodes happen.  Another critical time is at the start of rewind, but for
these areas even emergency splicing may be done with little data
loss.  So far
at least, all misbehaving cassettes and drives have conveniently
only damaged
either end of the media!  Of course, this has a lot to do with
the forces in
accelerating the tape and braking the tape to stop and would be the most
stressful part of operations.

Stuart M. Rohre
Univ. of TX Applied Research Labs A/D and Recording Facility