What Peter wrote is key to understanding sticky-shed. My chemist mentor,
Ric Bradshaw, formerly chief chemist at IBM tape division, suggests that
the original matrix is never recreated by baking so the repolymerized
longer chains are not as long as the original chains, but no longer
short enough to be sticky.
A few years ago, I visited the Library of Congress and happened to
mention that I was baking tapes for two days (1/4 and 1/2 inch, mostly).
The people I met with wanted to know more. They bake for about eight
hours and have good results. I rarely achieve my goals with that short
of a baking cycle.
LoC confirmed they were transferring their "captive" tapes which had
spent some time in their controlled storage.
I receive tapes from "the wild" and often they have been miserably
stored. There is a lot of humidity in many parts of North America.
Stuart Rohre bakes tapes 30 days now. these are 15-inch windowless glass
reels of 1-inch instrumentation tape which had been sent to sea in a
buoy to record a string of hydrophones. The machines were exposed to the
sea atmosphere just prior to launch. He can make a full pass on one of
these reels after the 30-day baking. So, to me, that seems to indicate
that those of us who bake two days still have some "headroom" left
before things get really bad.
I rarely go back and re-transfer tapes that I've baked, and if I do,
it's within a few weeks, usually (to see if I can improve a specific
aspect of a transfer).
If I have NR encoded tapes, I save both a raw and decoded version so I
don't have to go back to try and correct NR anomalies. In fact, I
provide both to the client. I started doing that on a 16T 1/2-inch tape
that had some tracks recorded with NR and some not and no documentation
as to which was which, and it was "new" music, so I just sent both sets
to the composer and said (nicely), "you figure it out." He was ecstatic
as the original machine when they did the analog mix would not allow
them track-selective NR switching.
On 2017-09-01 1:40 PM, Lou Judson wrote:
> This is quite a wordy explanation, and I do not doubt or argue with it. My only interest is in recovering tapes people bring me to transfer, and so far have had excellent success, baking 8 - 10 hours, cooling the some amount of time, and playing them then. I have not examined them later, the storage comment was third-hand anecdotal, not personal or scientific.
> But - can you please specify what you mean by “Short-term baking?” and is long-term better? How short, how long and what temperatures? Also, what do you recommend for long term storage after the treatment?
> Thanks. Peter.
> Lou Judson
> Intuitive Audio
> On Sep 1, 2017, at 10:27 AM, lists <[log in to unmask]> wrote:
>> Pardon for the very late posting (have been massively busy with disaster
>> recovery projects) but the posting concerning "sticky shed" truly needs some
>> clarification as the way it is stated is very misleading.
>> Sticky shed is caused by binder hydrolysis. This is indeed a function of
>> chemistry- but the chemistry involved is the interaction of water (often
>> absorbed from humid air) with the long-chain polymers in the tape resulting
>> in the polymers breaking down into short-chain, low-molecular-weight
>> While this is a chemical reaction, the reaction is very dependent on the
>> moisture content of the air in the environment in which the tapes are
>> stored. The assertion that " they return to the sticky state eventually,
>> even in perfect storage" is not correct. Should this happen, they have not
>> been placed in "perfect storage". It has, in fact, been proven that
>> "sticky" tapes (without baking) will become less sticky if stored in stable,
>> low-RH environments. If you store polyester-base tapes in an environment of
>> approximately 68 degrees and an RH of 20% or less, within a year, most (some
>> take longer) sticky tapes are no longer sticky and further testing 2, 3 and
>> 5 years down the road, show that the tapes continue not to exhibit "sticky
>> shed". As such, the "perfect storage" referred to in the earlier post is
>> not actually "perfect" storage for polyester-base magnetic tapes.
>> Another issue could be the method used for "baking" and how soon the tapes
>> are tested after they have been returned to storage. Many people perform
>> short-term baking. The issue with this is how hydrolysis affects the tape.
>> When hydrolysis occurs, polymers in the tape matrix as well as polymers on
>> the tape surface are effected. The oligomer residue created inside the tape
>> matrix may partially migrate to the tape surface. Heating the tape during
>> short-term baking primarily causes some of the oligomer residue to be
>> re-absorbed into the tape matrix leaving less on the surface and making the
>> tape, temporarily, playable. It has little effect on the oligomers other
>> than their absorption into the tape and away from the surface. As soon as
>> the tape begins to cool, these oligomers (slowly) start to migrate back to
>> the surface again. This is one of the reasons that individuals who do
>> short-term baking state that you must play back the tape as soon after
>> baking as possible. More sustained treatment (whether by "baking" or
>> exposure to very low RH environments or a vacuum) actually forces
>> cross-linking of the oligomer residue back into polymers. As such, there is
>> no great abundance of oligomer residue to migrate back to the surface and
>> the tapes (so long as they are not exposed to elevated humidity) remain
>> playable for an extended time.
>> This is likely more information about the subject than most people really
>> want to know but to state that "sticky shed" is not a function of "storage"
>> is extremely misleading.
>> Just as background, I was one of the primary authors of the National and
>> International Standards about magnetic tape storage and magnetic tape
>> handling published by ANSI, AES and the ISO.
>> Peter Brothers
>> SPECS BROS., LLC
>> [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 Lou Judson
>> Sent: Thursday, June 29, 2017 11:44 AM
>> To: [log in to unmask]
>> Subject: Re: [ARSCLIST] Cassette repair question
>> I believe it has been more or less proven that sticky shed is a function of
>> chemistry, not storage, as even after baking they return to the sticky state
>> eventually, even in perfect storage.
>> Lou Judson
>> Intuitive Audio
>> On Jun 29, 2017, at 5:11 AM, Steve Greene <[log in to unmask]> wrote:
>>> But bear in mind, the loss of the felt suggests that the tape probably
>>> wasn't stored in the best conditions, be concerned about sticky-shed,
>>> or other binder problems in your future.
Richard L. Hess email: [log in to unmask]
Aurora, Ontario, Canada 647 479 2800
Quality tape transfers -- even from hard-to-play tapes.