Hallo again:

LOL does not respond well to baking.  If the lubricant is gone, it is gone-
baking will have no effect.  If the lubricant has crystalized, the crystals
will melt near room temperature- again, no reason to bake. Note; both
assertions backed up by laboratory testing.   If you are baking standard
audio cassettes successfully, they probably have some degree of hydrolysis.
It appears somewhat different as the binder is thinner (less binder to
decay), the interface between the tape and heads is smaller (less surface
for frictional problems to be noticed) and many of the cassettes are not
backcoated (less tendency to hydrolyze so less oligomer residue).  We have
encountered many audio tapes with hydrolysis.  The effects on the tape just
appear different than on larger tapes.  It is one of the reasons I'm not
particularly fond of the popular term "sticky shed" when the actual problem
is "binder hydrolysis".  Hydrolysis can easily cause tapes to have a higher
frictional coefficient without significant, visible shedding.   Ok, "sticky
shed" sounds way cooler but it can obscure the actual chemical reaction that
is happening and result in incorrect assumptions.  If your audio tapes jam,
stick or run slow in your machinery and respond to "baking", the problem is
much more likely to be hydrolysis than LOL.

As for video tape, nearly all 1/2" open reel videotapes now exhibit
hydrolysis to some degree.  The majority of 3/4" video made between 1975 and
1985 also exhibit hydrolysis (ok, Il use "sticky shed").  Many Ampex 3/4
from this era are so bad that, when put in the playback machine, they almost
immediately seize up and will not move.  1" and 2" videotape also frequently
have sticky shed.

DATs, in my experience, not so much.  Yes DATs have problems but we have
been able to restore DATS to playable condition by cleaning and polishing
the tape surface- no baking.  The DATs are shedding and won't play back
properly but we have found they don't need baking- they seem to  just be
falling apart.  There is also a problem with the load mechanism in many DAT
machines that goes slightly out of alignment very easily and abrades the
tape during playback transport, causing additional shedding.  None of the
DAT info here is backed up by laboratory testing; just my experience.  If
others have had success with baking, there may be a hydrolysis issue.  We
may have just overcome the minor hydrolysis on the surface with the cleaning
and polishing.

Finally, a few thoughts on signal loss with baking.  It is possible that
baking might cause some irregularity on the tape surface.  I haven't seen
laboratory evidence of this, however, and we always clean tapes after baking
them so any irregularities would likely be smoothed out.  I have seen tape
under electron microscope[e that clearly shows tape surfaces are rougher
right after manufacturing than they are after a few record/playback passes.
I have always been amazed that there is no conclusive laboratory evidence
for the audio loss.  Everything is hearsay but it really should not be that
hard to set up an easily repeatable and fairly inexpensive test for this.

Another possibility is "thermal idiots".  Nice technical term but, hey, the
technical name for the insulating powder added to high density magnetic
recording mediums to counter superparamagnetic effects is "Pixie Dust".   In
any case, the magnetic particles on many older analog tape had a wide range
of coercivity and retentivity.  This is one of the reasons for print-through
where the lower coercivity pigments get affected by the magnetic field from
pigments in adjacent wraps.  Heat is also well known to weaken magnetic
characteristics of many materials (including those the magnetic pigments are
made of).  If low retentivity pigments are subject to heat, it is quite
possible they will lose or have the magnetic moment on the pigment effected.
This is one of the ways print through is treated- the tape is wound/rewound
and the low coercivity/ low retentivity pigments that picked up the print
through are scrambled by the combination of the mechanical shock from
transport as well as the  heat generated by the transport friction; and the
print through is reduced.  Just an idea as far as possible loss of signal
during "baking" is concerned, but it is consistent with magnetic theory.
This doesn't mean I am asserting that this is what is happening, as we
haven't seen a problem with signal loss, but it does match the science- now
we just need someone to do some controlled testing.



Peter Brothers
SPECS BROS., LLC
973-777-5055
[log in to unmask]
Audio and video restoration and re-mastering since 1983



  

-----Original Message-----
From: Association for Recorded Sound Discussion List
[mailto:[log in to unmask]] On Behalf Of Tom Fine
Sent: Wednesday, January 20, 2016 3:01 PM 
To: [log in to unmask]
Subject: Re: [ARSCLIST] One more sticky-shed data point - Richardson treated
tape

Hi Lou:

I agree, having transferred 1000+ cassettes over the years, that what we
call Sticky Shed has never cropped up. However, there have been cases of
Loss of Lubricant (LOL) or something similar, which has rendered the
cassette unplayable without baking. Baking has worked for me every time.
I've encountered this mostly with black-oxide off-brand cassettes, circa
1980s and early 1990s, some of which have been mass-duped (ie professionally
duped and packaged for mass-market release).

The other thing I have encountered, mainly with Scotch brand CRO2 tapes
circa 1980s and late 1970s, is terrible warpage that leads to the tape pack
sometimes being too big to fit in the shell. My solution to this has been to
very carefully hand-wind enough of the tape-pack over to one side so both
sides move comfortably in the shell, then splice one side into a new
cassette housing, transfer both tapes and edit together in the proper
sequence in the DAW.

By far the biggest problem I have encountered with cassettes is the pressure
pad having come unglued. I generally transplant those tapes into a new
shell. You can still find screw-together C-0 cassette shells out there for
sale, but I usually use one of hundreds of old Maxell and TDK tapes I've
accumulated into a big box, just for that purpose.

There has been talk out in the video world, some of it on the Ampex List,
about certain videotape brands that develop Sticky-Shed and/or LOL. There
are definitely some DAT types that develop something that makes them gooey
and non-playable. I've enountered this with TDK brand DAT tapes, and baking
has made them playable.

When Telarc Records was reissuing their Soundstream recordings, which were
on 1/2" instrumentation tapes, standard practice was to bake the tapes in a
convection oven. I don't know exactly what brand and type tapes they used. I
don't know enough about reel to reel digital tape systems to know if DASH
tapes need baking.

What is still mysterious to me is why some tapes of a type not known for
sticky-shed will go sticky. 
For instance, Shai has reported all kinds of problems with Scotch 206 in
Israel. I've never had one sticky 206 tape here in the US northeast. And the
same with vinegar syndrome. Some people report never having problems with
Scotch 111, yet my experience is about 50-50 whether a tape will go vinegar
and start edge-curling or not. Audiotape acetate-backed seems less likely,
but I've sure encountered my share of those tapes going vinegar. And yet
almost all types of 35mm acetate-backed audiofilm will go vinegar.

-- Tom Fine


----- Original Message -----
From: "Lou Judson" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, January 20, 2016 2:36 PM
Subject: Re: [ARSCLIST] One more sticky-shed data point - Richardson treated
tape


Here's a slightly offtopic question. I shared the post of Peters' with an
associate, with whom I am 
involved in a restoration project involving cassttes tapes from the 70s
through the 1990s. We are 
wondering why audio cassettes are so rarely having sticky-shed problems. I
know that has been 
discussed occasionally here, but why are cassetes relatively immune?

<L>
Lou Judson
Intuitive Audio
415-883-2689

On Jan 20, 2016, at 10:33 AM, lists <[log in to unmask]> wrote:

> Hello all:
>
> Coming very late to this thread.  I don't intend to talk here about Mr.
> Richardson's process but, in answer to Tom's post, I'll try to address
some
> of the issues with "sticky shed".