[AV Media Matters] Comments, experience on rewinding

[rohre@arlut.utexas.edu]

My library has had over a thousand Ampex (mainly) tapes over the years.

Although, we have not been able to faithfully carry out a regular rewinding
program, we have made spot checks, or our consultant Glen Schulze has, over
the years on the older archives.   The checking is done on a basis based on
date codes on the tapes, batch codes, and importance of the data thereon.

We have rewound before storing, any tapes that have, by heavy use for data
playback, developed poor packing of the edges.  (In data reduction use,
certain sections are spot played and digitized, and this can shift parts of
the pack).  Some machines will do this on some tapes even if the machine is in
proper path alignment.  I believe some tape slitting variation can cause more
or less of a tendency for a tape to pack poorly.  (This is more of a problem
on coaxial reel machines rather than the uniplanar tape path machines.)

Our findings, is that even backcoated tapes have cinched in storage.  Just a
few, but the bottom line is to look at any tape that has not been used in a
while before reuse.  Particularly, we have many master tapes or copies that
were NOT made on our equipment, and thus have an uncertain prior play/handling
history.  The inspection should consist of visual inspection of BOTH sides (!)
 and a simple stiction test. (I have seen one side start to cinch before the
opposite side, although that was a rare event.)

We simply take the belt off the reel for the spooling test, and allow a few
feet of tape to unwind by gravity, while holding reel high off the floor.  If
the tape "peels" away from the underlying layer rather than unwinding freely,
we are quite cautious in machine operations if any, and do not use fast
speeds. We do use machines to rewind that have good tape handling, and we
clean them in between tapes, including all guides.  Heads are removed and
replaced by dummy heads or an alternate threading path is used. (We have such
a machine, that allows the heads to be bypassed completely.)  All incoming
reel to reel tapes have this done before being mounted on our transports.

We have seen gumminess deposit upon guides, but after cleaning the tape and
guides, we have found no loss of recorded signal.  Most of our tapes are
recorded to full level, and we believe biased to create magnetized information
below the molecular level of the shedding observed.  Of course, we copy or
bake and copy such shedding tapes!

Over the years, we have found that changes in layer to layer tension happen,
in the air conditioned storage, apparently because of varying humidity.  (The
range of humidity seen inside the building can be in a year- 15% RH to 60%
RH.)  In addition to chilled water central air, we have added localized freon
units to try to dry the storage area air.

A number of the tapes that came to our archives from outside sources were made
in ocean research, and thus a high humidity environment aboard ship, even if
the research space was air conditioned!  Some of these during storage, started
emitting amine odors that are noticeable when the tape is replayed.  Those are
of course signs of stiction developing, and rewinding removes the gases that
might accumulate inside solid sided glass master reels that have tape seal
belts to keep out dust.  However, the appearance of the chemical sharp smell
of amine generation is not just a case for rewinding, but at that time of
identifying such a tape, a copying process to recover and preserve the data on
new media must be undertaken.

Jim Wheeler probably knows of a tape archive I heard about from other Ampex
persons.  That one stores tapes in an open office type environment, and had
masters in good shape that well exceed 30 years old.  There was a change of
lubricant used in tape manufacture some years ago, and we have some archives
of 22 year old tape that is in better condition than tapes made at the time of
the manufacturing change from natural to synthetic lubricants.  Generally, we
have seen no storage problems with our Ampex video tape formats, but they are
back coated types.

However, I have personal Video VHS archives that have suffered in home storage
in a cabinet environment in an airconditioned living space.  These were
exclusively non Ampex brands, but included most of the well known overseas
brands.  Most of the problems have been poor packing.  A few have developed
speed variation, which must indicate stiction.    Because most of these tapes
had been used on one or more of only three (dependable) machines, and have not
been frequently played, it appears that casual storage (home) environments may
give varying results with video tapes.

I have seen quite a few variations with 8mm tapes used for computer back ups,
in a lab environment.  However, close study of these seems to identify 8mm
drives as the culprit here.  If they reread a section of tape frequently, they
may affect its winding and storage life.  (The data grade tapes were being
used, not video grades on data machines.)

Also, we found this to be true of using 4mm Computer tapes.  Some bad drives
caused us no end of problems while using high quality tapes.  Any brand did
poorly, until the drive was replaced, and the drive was only months old.  We
have some evidence that manufacturers of small format drives do random sample
testing, and if the production line gets out of adjustment, this might not be
caught before some badly aligned drives slip thru.  We suffered this as well
on 2 SVHS digital transports where the digital wrap around vendor was not
using test tapes to confirm the transport maker had aligned the tape path
correctly to the drums.

Thus, although back coating has been a blessing to the tape users, I would say
one should be careful to keep storage at good conditions for  tapes or film,
and should inspect tapes before each reuse, if the data is valuable.  Thus, to
be sure, after you think the tape is in good condition and can be played, stop
after a few feet and examine the tape and drive for any shedding before things
get out of hand.  You really do not want to be looking at clear mylar after
playing a tape!

Stuart M. Rohre
Recording Lab
Applied Research Laboratories of the Univ. of Tx Austin