I'll dip my toe in with an observation. Most of my experience has been
with 3/4" u-matic tape from the early 80's.
I have always been amazed (jealous) when I read results here about
recovering audio after 8 hr or 1 day of baking.
When I encountered U-matic tapes going (gone) bad I started out trying
to bake a day or two but quickly came to the conclusion that I was
wasting my time re-assembling the tape housing and testing in a video
machine. As opposed to audio tape machines, testing video and
re-cleaning the machines is more laborious (my guess).
Now when I confirm a bad tape I stop the play back immediately. Shells
are open-up and then I feed de-humidified air into the back of an oven
with a blower set to 135 F for a min of one week at which point I may
test a tape or two and if it fails, the another full week.
The longest I baked material was 4 weeks at which point the heads were
still clogging up after 20 min, so I cleaned and continued and stitched
the video together afterwards.
I would typically bake 12 u-matics at a time, preferably in the fall or
1) do not worry about ruining high frequency content on audio tape.
Video tape is ALL high frequency (Mhz) and the baking allows the signals
to be recovered .
2) I suspect the width of the tape is a big factor as well as humidity.
If temp alone mattered then baking a 1/4 in tape or a 3/4 in tape would
reach thee same temp within an hour easily).
3) I suspect it takes exponentially longer for the dry air to have an
affect wider tapes.
1) I suspect a gadect which continually wound a tape back and forth
between two reels slowly in an oven would speed up the process for video
Off to try and give away a working Webbcor 210-1c in the GTA (free)
On 9/1/2017 2:02 PM, Richard L. Hess wrote:
> 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
>>> 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
>>> absorbed from humid air) with the long-chain polymers in the tape
>>> in the polymers breaking down into short-chain, low-molecular-weight
>>> While this is a chemical reaction, the reaction is very dependent on
>>> moisture content of the air in the environment in which the tapes are
>>> stored. The assertion that " they return to the sticky state
>>> 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
>>> 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
>>> 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
>>> are tested after they have been returned to storage. Many people
>>> 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
>>> 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
>>> 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
>>> want to know but to state that "sticky shed" is not a function of
>>> is extremely misleading.
>>> Just as background, I was one of the primary authors of the National
>>> 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]>
>>>> 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.
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