Hi, Mike,
I replied on the Ampex list, but will here as well since there are many people who are not on both lists.
Tom: <blush>
At 11:39 AM 6/4/2006, Mike Csontos Mwcpc4@xxxxxxx wrote:...About twelve years ago I salvaged tape from a local studio's radio commercial masters for editing transfers of some oral history material for cassette access. The tape was in Ampex 291, 414, 405; 3M 201, 175, and many white boxes, various lengths.
I found that black oxide back coated tape was useless because of SSS, non-back coated tape was fine, regardless of oxide shade, and brown oxide back coated tape seemed OK. At the time I thought the SSS was a function of the oxide, not the backing so I interspliced the scraps of brown coated and non-back coated tape.Obviously mixing types of tape on a single reel is not good practice and nobody on this list would do that, but this provides some idea of the wide variation of tape condition over time even under identical storage conditions (on the same reel).
Mike,
I have been digging into this issue for several months now and I am not much closer to an understanding than I was when I started. In fact, the more I learn, the more I need to learn.
I have been reading "Tribology and Mechanics of Magnetic Storage Devices, 2nd Edition" by Bharat Bhushan and have been talking to a bunch of tape people.
What we think we know about why baking works may not be the whole truth - I don't have a good summary yet as to what the truth is, but chemists smarter than I have told me this.
There are perhaps 5-10 possible causes of squeal, and there is no easy method yet to diagnose what the cause is. Without a diagnosis, any attempted cure is craft not science. It's not that craft is bad, it gets the job done, but I much prefer to understand.
One thing I have learned is that polymer chemistry/mechanics/physics is VERY complex and, in fact, not necessarily completely understood by former practioners. The science has advanced greatly in the last twenty years in data tape, only some of that has filtered back to audio tape. I'm not sure about video tape as I haven't been researching that.
Yes, there appears to be a correlation between back coating and SSS. In an informal survey I took a month or so ago with one exception all tapes that have responded to baking have also been back-coated.
Most if not all tapes that squeal and do not respond to baking are NOT back coated. We have been calling these "loss of lubricant" tapes but, again, there are many hypotheses relating to the cause of the squeal, and most do not involve an actual loss of lubricant.
I feel that I'm back at square one, but will keep digging.
I think the only safe thing to say is that we cannot predict with certainty the expected lifetime of any single reel of tape. I know it sounds self-serving to say this, but if the tape is important, it should be digitized.
While in this thread (and previously), Tom Fine has reported excellent results with 111, I have seen some MINOR degradation starting to set in on 111, and there have been some reports on vinegar syndrome advancing on 111--rare, but not unknown.
It appears that while I thought it didn't matter when you baked, it's now looking as if the degradation is progressing and hasn't necessarily stopped.
I think if the tape is acetate or is on any of the known bad tapes, it definitely needs to be transferred sooner rather than later.
Some known bad tapes are listed here: http://richardhess.com/notes/2006/05/17/sticky-shed-loss-of-lubricant/
You can find the above article and a growing collection of tapetravesties at http://richardhess.com/notes/category/archive-operations/tape-aging/
Some people suggest not trusting important tapes past the age of ten years. One of these is a person who led tape making at a major manufacturer.
One copy of anything important is always a huge risk, but has been the norm.
Cheers???
Richard
Richard L. Hess email: richard@xxxxxxxxxxxxxxx
Aurora, Ontario, Canada (905) 713 6733 1-877-TAPE-FIX
Detailed contact information: http://www.richardhess.com/tape/contact.htm
Quality tape transfers -- even from hard-to-play tapes.