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ARSCLIST  December 2009

ARSCLIST December 2009

Subject:

Re: Tape Degradation Modalities

From:

Marie O'Connell <[log in to unmask]>

Reply-To:

Association for Recorded Sound Discussion List <[log in to unmask]>

Date:

Fri, 18 Dec 2009 17:27:08 +1300

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (161 lines)

As usual Richard, fantastic work!  Thanks so much for putting this together.

Cheers
Marie
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
> http://richardhess.com/notes/index.php?s=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 -10C <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:
> http://richardhess.com/notes/index.php?s=sticky+shed
>
> 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
> http://www.richardhess.net/restoration_notes/USP5236790.pdf
> 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
> temperature.
>
> 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.
>
>
> http://richardhess.com/notes/2008/02/15/winding-tapes-for-long-term-storage/
>
> 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.
>
> http://www.richardhess.com/tape/scallopped.jpg
> http://www.richardhess.com/tape/oval_pancake.jpg
>
> 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.
>
> Cheers,
>
> Richard
>
> 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.
>

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