On 2015-04-07 3:18 PM, Eric Jacobs wrote:
> 2-inch tapes with sticky shed may not respond as well to baking as
That is true in the sense of in the same or similar time frame.
I don't think there are precise formulae for predicting the time either
to achieve thermal equilibrium or to achieve moisture equilibrium in a
tape pack. Vos (1994) inspired me to develop a rule of thumb that
moisture equilibrium appears to take 1500 times as long as thermal
equilibrium in a one-inch tape, based on my extrapolations from his curves.
We have long suspected that the width of the tape was a large modifier
of this ratio. I based my estaimate on Vos's graphs which seemed to
indicate that a 1-inch tape pack, might achieve thermal equilibrium
might in 100-200 minutes while it might take 100-200 DAYS to achieve
moisture equilibrium. I felt that a factor of 1440 implied far too much
precision in the calculation, so I rounded it to 1500.
Further pointing to this is what Stuart Rohre has reported on the Ampex
mailing list and elsewhere. He has been responsible for retrieving the
most information possible from some 1-inch instrumentation tapes which
are 15-inch diameter tape packs on glass precision Corning reels with no
windows. The windowless reels further slow moisture diffusion. He had
originally said they were baking for several days and could get through
about half the tape and then had to rebake, but they also had to run the
tape through their Bow tape cleaners. Partially at my suggestion and
partially on his own initiative, Stuart found that if he baked the tapes
for 30 days, they would play through without the need for any tape
cleaning or re-baking and he was getting very clean signals off the
tapes at that point.
So, are the two-inch tapes not responding to baking or simply in need of
more of it?
One 7-inch reel of 1/4-inch tape that had been exposed to high humidity
cycles overnight had a very easy-to-remove mag coat when first
inspected. When it was stored in my air-conditioned home (minus the
economizer cycle bringing in Los Angele's famed "Marine Layer" of "night
and morning low clouds") for 3-4 months, the same test that initially
showed mag coat removal could not be duplicated and the tape binder
seemed very secure at that point.
The "more baking" concept pertains to tapes like Ampex 456, 406, and 407
as well as the instrumentation tapes made by Ampex at about the same
time. It may also apply to Scotch 226 and 227 and possibly Scotch 250.
It probably does not apply to Agfa tapes which have some of their own
This web page attempts to categorize tapes by degradation modality, and
degradation modalities are currently described more by what can
ameliorate their effect than by the actual chemical/mechanical failure
modes. My decade-long goal of a "pool-test kit" for tape degradation
measurement is farther in the distance than it was when I started the quest.
Richard L. Hess email: [log in to unmask]
Aurora, Ontario, Canada 647 479 2800
Quality tape transfers -- even from hard-to-play tapes.