As usual Richard, fantastic work! Thanks so much for putting this together.
PS. Off to the work Xmas party and no, there will be no Isopropyl
concoctions there tonight ;-) Just the good stuff!
On Fri, Dec 18, 2009 at 3:47 PM, Richard L. Hess
<[log in to unmask]>wrote:
> Hi, All,
> We are potentially conflating many different tape degradation modalities in
> this current and fascinating discussion.
> Some of them are:
> Squealing tapes
> These are usually NOT back-coated and may respond to cold soak, lubricated
> playback, fast playback, and low tension/single head reproducers.
> As to The Last Factory tape products, I found I had to use much more than
> recommended and with cassettes and reels that were not back coated but
> squealed, I got minimal results. I find that Decamethylcyclopentasiloxane is
> a more cost-effective and safer lubricant--safer in the sense that it
> evaporates and does not appear to create any chemical reactions with binder
> nor head. You can flood a machine with it which will cause all the friction
> components to stop working, but the liquid will eventually evaporate.
> This is discussed on PDF page 23 (Journal page 260) of my ARSC article
> available at www.richardhess.com/tape/history/
> Since GE is interested in selling tank cars of this lubricant, a quart
> sample can often be pried loose for this application.
> Here are references in my blog to squeal
> In my limited experience, squealing tapes that I have baked have not been
> helped by the baking and the baking may have made the squeal worse.
> I discuss this in my ARSC paper (originally presented at the AES) which was
> where I originally announced the cold playback technique. As a reminder, the
> squeal is at least partially attributable to the symptom of lowered Glass
> Transition Temperature (Tg) of the mag coat. If the Tg is below the playback
> temperature, then we're trying to play back rubbery-rather-than-smooth
> tapes. Cooling the playback system has helped in many cases. I have yet to
> take the playback system below freezing (though tonight would be a good time
> to try at -10°C <smile>).
> Also as a reminder, what shocked me was when we discovered what appeared to
> be a complete lubricant load in a tape--but the tape still squealed. This
> was with Sony PR-150, the other poster child for squealing tape along with
> 3M175. So, we really can't call it "loss of lubricant". That's why I
> introduced the term Soft Binder Syndrome (SBS) and also proposed that SSS
> (see below) was really a specialized subset of SBS that was cured by baking.
> As an aside, the above taxonomy partially confuses current states by naming
> them based on
> (a) how the tape got to the current condition
> (b) how the tape behaves now
> (c) how we cure the current failure
> Since we do not have definitive tests for specific failure conditions of a
> tape, we are a bit like being in Plato's cave and we merely see the shadows
> on the wall--we really don't know what is happening at the molecular level.
> A Ph.D. physicist friend says that all chemistry is physics anyway at this
> level as we're talking about bonds and how they break. So, I'm afraid we
> must be content in our un-funded chem-physics labs to identify problem
> states of tapes by those very shadows--the only things we can actually see.
> Sticky Shed Syndrome (SSS)
> I have several articles, including the first publication of Marie
> O'Connell's isopropyl drip method that you'll find here:
> I thought it was "common knowledge" that baking times are going up. I
> generally bake for at least 24 hours now, even for 1/4-inch tape. In fact,
> if we look at the Ampex patent which I have made available here
> even back in the day they were proposing 12 hours in claim 4. They also
> talk about both
> 50° C and 54° C. That's 122° F and 129° F. I generally use the 54° C
> I cannot recall baking any non-back-coated tape with any success, although
> one correspondent did recall success with one batch, but that may have been
> a batch of normally back-coated tape that was custom-supplied without the
> back coating.
> While SSS tapes can squeal, since the problem is easily ameliorated by
> baking, I don't think we really mean SSS tapes when we say "squealing".
> Squealing (as discussed above) is generally a condition that is not helped
> -- and perhaps made worse -- by baking.
> Inter-Layer Adhesion
> This problem may happen with or without SSS or squealing. As I stated
> previously, I have had some success with 3M176 with cold soaking, but have
> not had any follow-on successes with that technique, but have with slow
> unwinding. Steven Smolian brings up a good point in discussing the "crotch"
> of the tape pulling off the reel. Just as peeling off a sticky label from a
> surface, the angle that it is pulled off at can be critical.
> I think more work needs to be done with wedges that can lift and separate
> the outer strand from the underlayment as well as potentially a roller that
> controls the angle of lifting right at the tape pack.
> The British Library work on the "Grandfather Clock" is the largest effort
> addressed to this that I'm aware of. I'd like to hear more about Steven's
> technique about lubricating -- or perhaps we should consider this more of a
> "release agent" that helps separate the face of the mag coat from the
> adjoining basefilm.
> I have not seen much discussion of the relation of pressure effects, but
> Bhushan did discuss it in his second book. I've discussed this here --
> please excuse the mess that happened during a WordPress update to some
> characters. Grrr.
> These same stresses and pressures can relate to inter-layer adhesion and
> explain why the problem is almost always worse closer to the hub. This is
> the converse of hub collapse which causes other problems like the
> "scalloped" tapes I found in the Mullin-Palmer collection.
> The leader tape issue is a special case of this. Otherwise well-behaved
> Maxell UD35 tape that I used in the mid-1970s has lost the first wrap on
> several album masters that I recorded and spliced in 3M printed leader tape.
> That's why we have safeties. The digital files are made from the master
> except for the first few seconds which are from the safety.
> I hate it when this happens. I have been using paper leader tape for all my
> post 1999 restoration work.
> Anyway, I hope this helps to clarify a bit and focus the discussion. Going
> forward, we should be careful about discussing one degradation modality per
> thread and not let the thread wander too far, though I wll admit to
> partially causing it by mentioning the multiple uses of the Racal machine. I
> hope everyone here who is doing this work understands the shifts between EQ
> that occur at different speeds. Magnetic Reference Labs publishes tables and
> a little program that lets you calculate many of these or you can plug the
> time constants into a spreadsheet and figure it out.
> Richard L. Hess email: [log in to unmask]
> 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.