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On 2015-04-07 3:18 PM, Eric Jacobs wrote: > 2-inch tapes with sticky shed may not respond as well to baking as > 1/4-inch. > 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 nastiness. 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. http://richardhess.com/notes/formats/magnetic-media/magnetic-tapes/analog-audio/degrading-tapes/ Cheers, Richard -- Richard L. Hess email: [log in to unmask] Aurora, Ontario, Canada 647 479 2800 http://www.richardhess.com/tape/contact.htm Quality tape transfers -- even from hard-to-play tapes.