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.
SPECS BROS., LLC
[log in to unmask]
Audio and video restoration and re-mastering since 1983
From: Association for Recorded Sound Discussion List [mailto:[log in to unmask]] On Behalf Of Richard L. Hess
Sent: Monday, January 25, 2016 2:42 PM
To: [log in to unmask]
Subject: Re: [ARSCLIST] One more sticky-shed data point - Richardson treated tape
Thank you, Peter!
To quote your earlier message (a paragraph that did not register amidst all the other wonderful paragraphs (2016-01-20 13:33 -0500)
> All that said, hydrolysis of the polyester binder is not the only
> decay vector identified in/on magnetic tape. Laboratory testing has
> identified a number of other decay residues. Among these are cyclic
> tri-mers from the polyester base, sodium or calcium impurities from
> the magnetic powder, various fatty acids or stearates from the
> lubricant and surfactants left over from the manufacturing process. Further testing has shown that "baking"
> does not seem to have a positive or "corrective" effect on these other
> residues. In some testing, "baking" has made the surface effects of a
> few of these other residues worse.
Is it possible to relate any of these to the rubberization of the binder as indicated by the lowering Tg symptom?
Is it possible to indicate further symptoms/indicators that can identify the following (I'm not fully giving up my idea of the tape version of a "pool test kit" if some meaningful restoration information couild be
---cyclic tri-mers from the polyester base
---sodium or calcium impurities from the magnetic powder
---various fatty acids or stearates from the lubricant and surfactants left over from the manufacturing process.
I agree with you that baking is not a 100 % cure-all, which is why I've advocated for cold playback, D5 lubrication, and fast playback over "sharper" profile heads as alternatives for squealing tapes.
You question about a specific flavour of mag coat shedding is interesting. One of the things that Jim Wheeler taught me (which he may have received from you) is "cold soak." I have struggled to understand what that does. We can assume that it drys out the tape (which is generally good), but I have also had some limited success with it reducing "pull out" damage from mag coat adhering to the previous layer's back (which is raw base film, not back coated).
One possible scenario I see in that is along the lines that you
discussed: as the tape cools and the moisture content is reduced by the desiccant in the sealed environment, there is microscopic motion of the mag coat matrix--enough to break loose the adhesion (dare I suggest interlocking asperities?) in a manner that is less destructive than pulling the tape off the pack. I am thinking that it may be more of a shearing action while the tape is still packed.
Unrelated in a sense to your question, but we've both come up with microscopic motion as a possible explanation. I have never actually seen the issue that you describe, but I have received two tapes in the past year that had horrible shedding and cold soak did not help one. Both of these were so bad, I was finding mag coat on my clothes and hair and skin! These were not the individual mag particles, but mm sized flakes of mag coat.
Speaking of dimensions, do you have a guess of the amount of differential movement we can see in the mag coat face due to any of these effects? Putting in perpective, the wavelength of 15 kHz at 15 in/s is 0.001 inches--1 mil. We see destructive azimuth errors certainly around 1/4 of a wavelength offset and probably less, but at 3.75 in/s we have a wavelength 1/4 as long as at 15 in/s so 1/16 of a mil is likely to produce audible effects at 3.75 in/s. Is that the order of magnitude of mag coat face warpage (independent of base film warpage) that you might expect to see?
On 1/25/2016 1:52 PM, lists wrote:
> Good summary.
> As I indicated in an earlier post, binder hydrolysis is not the only
> decay vector in magnetic tape. Baking will not cure 100% of the
> problems. I listed in my post about half a dozen other decay residues
> that have been detected and analyzed in the laboratory that were not
> binder hydrolysis. The interaction of different residues may have
> effects that have not been tested. Unfortunately, with the demise of
> tape, the huge labs with the expensive equipment set up to analyze
> these issues (often at a considerable cost) are not as readily
> available. We know a lot about hydrolysis since it was detected as a
> major issue and studied. It is not, however, the only issue.
> Here is a weird one that I cannot come up with a scientific answer
> If a tape (backcoated or not- happens to both types) throws a loop or
> cinches- and the oxide from one wrap is pressed tightly against the
> oxide from the adjacent wrap in the pack- and remains that way for a
> while (timing not determined); the oxide layers that are touching
> each other will occasionally fall off the tape when the tape is
> unwound. It falls off in a "sheet" across the entire width of the
> tape and for as far along the tape as the two oxide layers are in
> contact. This is not an issue of the oxide layer cracking where it
> is folded over and "peeling" off as the heads hit the crack/crease.
> We have unwound some of these tapes by hand (very slowly) and the
> oxide layer just falls off the tape. It is also not an issue of the
> oxide layers sticking together, overcoming the oxide/base adhesion
> and ripping off. The "sheets" of oxide are not adhering to the base
> layer and are not adhering to each other. They appear not to be
> adhering to anything- they just fall off- very strange.
> The only thing I can come up with is that the oxide layers and the
> backcoat have different frictional properties. In addition to all
> the other ingredients, the oxide layer of many tapes have an
> abrasive. It is possible that the frictional coefficient of the
> oxide layers cause them to "lock" together to some degree when they
> are pressed tightly together inside the pack. If the tape is exposed
> to temperature changes, the expansion/contraction of the pack, with
> these two contacting oxide layers "locked together" might,
> eventually, be enough to loosen the binder adhesion to the base.
> This is pure speculation but I can't come up with another
> explanation. Any guesses?
> 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
> Richard L. Hess Sent: Monday, January 25, 2016 10:52 AM To:
> [log in to unmask] Subject: Re: [ARSCLIST] One more
> sticky-shed data point - Richardson treated tape
> Hi, Shai,
> The lowering of the Tg is a symptom and has to be caused by
> something. It is not as if there were a "Tg knob" to turn that down.
> There has to be a cause.
> I do not know whether or not hydrolysis is the engine behind the
> lowering of the Tg. Tg is like body temperature. You might find a way
> to lower your temperature, but the doctor would like to find the
> underlying (root) cause.
> I'm not ruling out Tg drops begin caused by hydrolysis...what other
> degradation modality might cause this? I will accept that hydrolysis
> may not always result in sticky shedding.
> That is why I started to create a symptom- and cure-based taxonomy of
> failure modes and why I thought "Soft Binder Syndrome" (caused by
> hydrolysis or not) was a good over-arching category with the Venn
> diagram circle for traditional sticky-shed syndrome included
> completely within the SBS circle.
> On 1/25/2016 9:44 AM, Shai Drori wrote:
>> No, I think Richards theory about the Tg is accurate about cold
>> play. These tapes do not show any of the signs of SSS but do
>> respond to other methods. Have I missed anything and someone was
>> able to play them fine after baking?
>> Cheers Shai Drori Expert digitization services for Audio Video Hi
>> Res scanning for film 8mm-35mm www.audiovideofilm.com
>> [log in to unmask]
>> On Mon, Jan 25, 2016 at 2:45 PM, Tom Fine
>> <[log in to unmask]> wrote:
>>> I'm wondering if this is an extreme case of what I've been
>>> theorizing about the surface getting degraded from going sticky
>>> and then being baked. Maybe the Sony and 3M tape that Richard has
>>> to cold-play have a surface so screwed up, either because it goes
>>> very un-smooth or something happens where binder material "dries
>>> out" so it doesn't shed but remains somewhat "rubbery" right at
>>> the surface have a chemistry that makes hydrolysis particularly
>>> damaging to the physics of the material?
>>> -- Tom Fine
>>> ----- Original Message ----- From: "Shai Drori"
>>> <[log in to unmask]> To: <[log in to unmask]> Sent:
>>> Monday, January 25, 2016 1:03 AM Subject: Re: [ARSCLIST] One more
>>> sticky-shed data point - Richardson treated tape
>>> High Richard
>>>> I think we had a discussion about these two in the past. The
>>>> PR-150 has some batches that run fine but most do squeal. I
>>>> haven't even tried baking them except once just for the hell of
>>>> it and of course no luck. Double speed playback works when
>>>> possible but I haven't had any lately so haven't tried cold
>>>> play yet.
>>>> Cheers Shai Drori Expert digitization services for Audio Video
>>>> Hi Res scanning for film 8mm-35mm www.audiovideofilm.com
>>>> [log in to unmask]
>>>> On Mon, Jan 25, 2016 at 6:10 AM, Richard L. Hess <
>>>> [log in to unmask]> wrote:
>>>> Hi, John,
>>>>> This is indeed true. HOWEVER, my success rate for baking
>>>>> tapes that are suffering from squealing and/or deposition
>>>>> that are not back coated is much lower.
>>>>> This raises another question. If all binder breakdown is
>>>>> hydrolysis, then why doesn't baking cure it 100%? I'm
>>>>> thinking of Sony PR-150 and 3M-175.
>>>>> These two seem to show the falling Tg, but don't have the
>>>>> shedding. They are outliers and inconsistent.
>>>>> On 1/24/2016 3:41 PM, John Schroth wrote:
>>>>> Back-coating may instigate or speed up the hydrolysis process
>>>>> but I
>>>>>> cannot ignore the fact that there are still obscure
>>>>>> instances where the tape had no back-coating and suffered
>>>>>> from SS. Richard, you have noted this in the past and I
>>>>>> have had this happen in at least two instances that I can
>>>>>> recall. I'm at home today so I don't have access to my
>>>>>> notes, but it was clearly sticky shed on tapes that had no
>>>>>> back-coating. So one should not "always" equate
>>>>>> back-coating with sticky shed.
>>>>>> Just my two cents...
>>>>>> John Schroth MTS
>>>>> 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.
Richard L. Hess email: [log in to unmask]
Aurora, Ontario, Canada 647 479 2800
Quality tape transfers -- even from hard-to-play tapes.