Peter, Thank you!

If there is pinning on a tape, resulting in pull-outs if unwound even at 
slow speeds, I have found that the "cold soak" will break the pinning 
bonds in a less destructive manner than unwinding...sometimes.

I wonder what causes the pinning. I have started to think that its 
moisture--a lot of it--working its way in there and hanging around for a 
while. One of the badly pinned tapes that I worked on as part of a 
workshop was apparently stored near a broken attic window...in Oregon. 
Where it rains. Alot.

The late Peter Copeland (I'm writing "the late" far too much these days) 
from the British Library developed his "grandfather clock" (my historian 
brother-in-law grimaces at that and much prefers "tall case clock" 
<smile>) which unwinds the tape at about 1 rpm and then blows hot air 
over the strand before rewinding it onto another reel at the bottom of 
the tall case. The part where the pendulum would normally go is the 
drying chamber and the tape is in there for quite a few minutes.

He found this worked especially well with ultra thin (3600 feet on a 
7-inch reel) tapes.

Is it safe to say that the other three degradation modes apparently do 
not produce anything that impedes playback (except they can generate 
spacing loss)?

I did have an interesting experience with one tape that was kept in a 
library where the humidity plot looked as if they were hosing the place 
down every night--turns out they were forced to run an economizer cycle 
and the moist ocean air drifted in overnight with nightly peaks to 80% 
or so RH.

Many of the white-box, black mag coat, no back-coated tapes had "clear 
leader" that was not spliced on. It was rather easy to extend the length 
of that "leader" by slightly shocking the tape. I brought one tape to my 
home (then in Glendale, CA, rather dry and well air-conditioned) and 
after a few months, the mag coat was no longer susceptible to removal by 
mild shock, and played find. I had not gotten around to sending to The 
Last Factory where they were going to experiment with vacuum desiccation.

The entire archive was copied to two sets of audio CDRs. This was long 
before the ubiquitous application of computer audio and it was crowd 
sourced.

Cheers,

Richard



On 1/25/2016 3:48 PM, lists wrote:
> Richard:
>
> Most of the identified decay residues appear as a "white powder" or
> "crystals" on the surface of the tape.  In some instances, they leave
> an almost undetectable residue that results in a "sheen" on the tape
> heads.  None, per se, were identified as having the effect of causing
> the surface to be "rubbery" but limited testing was done after the
> residues were identified.  The testing was done in reaction to an
> imagined health concern about the composition of the detected
> residues that was, luckily, found to be a non-issue.  Not saying you
> want to start "snorting" these residues but the misidentification of
> the residues that prompted the testing was found to be untrue.
>
> As for "cold soak", yes, that was developed in our lab- we called it
> "cold desiccation".  I shared the data with Jim Wheeler and he passed
> it along.  It is one of the ways we showed that oligomers could be
> cross-linked back into polymers.  One of the issues with cold
> desiccation is that any oligomers that have migrated to the tape
> surface are not reabsorbed into the binder (such as happens with
> baking).  If large amounts have migrated to the tape surface, you can
> actually reform polymers on the surface (which can cause another
> problem altogether).  There are a number of reasons why this
> procedure can work to reattach loose oxide to the base.  One of them
> is that the bonds which hold the binder together are similar to the
> bonds which hold the binder to the base.  By forcing cross-linking of
> oligomers on the underside of the oxide layer, it is possible to
> strengthen or "re-attach" the weakened bonds between the oxide and
> the base.  In addition, cold will cause contraction of the tape
> material but the primary vector of the expansion/contraction is the
> thickness of the tape.  By exposing the tape to cold conditions, this
> loosens the tape pack.  The combination of a loosened pack with a
> reforming of some of the bonds between the underside of the oxide and
> the base, can keep the oxide layer on the tape long enough to get a
> playback.
>
>
> Peter Brothers SPECS BROS., LLC 973-777-5055 [log in to unmask]
> Audio and video restoration and re-mastering since 1983
>
>
-- 
Richard L. Hess                   email: [log in to unmask]
Aurora, Ontario, Canada                             647 479 2800
http://www.richardhess.com/tape/contact.htm
Quality tape transfers -- even from hard-to-play tapes.