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

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