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ARSCLIST  December 2009

ARSCLIST December 2009

Subject:

Tape Degradation Modalities

From:

"Richard L. Hess" <[log in to unmask]>

Reply-To:

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

Date:

Thu, 17 Dec 2009 21:47:45 -0500

Content-Type:

text/plain

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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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