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 -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:
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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