Hi, Tom,
Two chemists I've worked with on this, Benoit Thiebaut who was at the
Natural History Museum in Paris and Ric Bradshaw from IBM both have told
me I'll never get the "pool test kit" that I had hoped when I started
this investigation a while ago.
While I do not want to discourage Sarah from coming up with it when
other say it's impossible--that's just a challenge for some--here are a
few items to consider.
(1) Benoit found out that at least one Sony U-Matic cassette type number
had four different binder configurations (and not just minor
differences). I think I've referred to "running changes" being made in a
particular type number without changing the type number. We believe that
happened fairly frequently at Ampex.
This means that the same type number (U-Matics are easier to deal with
as the housing is clearly identified as to type and one does not have to
rely on the tape being in the original box or on the original reel as we
do with reels) can show very different degradation characteristics.
(2) Some of the degradation products are unreacted original components
of the manufacturing process. It is widely understood that
batch-to-batch consistency was not all that great, especially with Ampex
tape. This may also contribute to differences in aging and degradation
among different samples of the same tape type.
(3) It is believed that storage conditions over the years can create
differing degradation states. For instance, my comment that the LoC is
not seeing the necessity for extending baking times that you and I have
discussed.
So, even if we thought we knew for one tape, we don't really know. There
is a substantial cost to perform these tests and evaluations.
Some of the expensive techniques in use are:
Fourier Transform Infrared Spectrometry (FTIR)
====================================
http://en.wikipedia.org/wiki/Fourier_transform_infrared_spectroscopy
http://mmrc.caltech.edu/FTIR/FTIRintro.pdf which says, in part
"So, what information can FT-IR provide?
. It can identify unknown materials
. It can determine the quality or consistency of a sample
. It can determine the amount of components in a mixture" (p. 2)
Here is a discussion of the use of FTIR for tape analysis.
http://www.morana-rtd.com/e-preservationscience/2011/GomezSanchez-13-06-2010.pdf
Here is the cite for Benoit's work:
Characterization of U-matic videotape deterioration by size exclusion
chromatography and pyrolysis gas chromatography/mass spectrometry and
the role of adipic acid
/Journal of Cultural Heritage/, Volume 10, Issue 2, Pages 183-197
Benoît Thiébaut, Léon-Bavi Vilmont, Bertrand Lavédrine
Mass Spectrometry
===============
http://en.wikipedia.org/wiki/Mass_spectrometry
What I have seen from this is a spectrum showing molecular mass of
various components of the analyzed substance. The molecular mass values
are measured in grams per mole.
What I recall is that there is roughly a decade variation between the
three types of substances of interest:
50,000 g/mol for binder
5,000 g/mol for sticky stuff
500 g/mol for lubricant
So when you look at a mass spectrogram and see a large spike around
50,000 and one around 500, that is normal. How Benoit helped show me
there was no loss of lubricant is we could still see an average-height
spike at 500 on a tape that squealed, but we saw a much bigger spike at
5,000 than in a normal tape. The roughly 5,000 g/mol material is the
sticky stuff and it's broken off the 50,000 g/mol material in many
instances.
Now going beyond this is a Ph.D. chemist exercise and very few
knowledgeable ones are worrying about this anymore. Benoit has gone on
to other disciplines, Ric is in private consulting, and Bhushan is no
longer interested in tape--he's focusing on nano technology. Ric has
helped me greatly but Bhushan basically said he was not interested in
helping even when he knew Ric had asked me to ask him.
Benoit's work in Paris was funded by PrestoSpace and they own it.
Bradshaw's and Bhushan's work is best summarized in Bhushan's two tomes
on magnetic media and the collection of individual papers cited therein,
though most are summarized in the books.
So now we know how to look at tapes using expensive tools that require
an advanced degree to really understand and where are we? We've learned
about the individual reel of tape we're working on. It might tell us
something about a small group but, since in audio, we cannot easily
identify tapes without an FTIR device, it's never going to be a
pool-test kit.
Science likes to work on advances most of the time. We saw what happened
when IPI looked at this -- they did not come up with meaningful results
and they are Ph.D. chemists.
Here are two LoC summaries:
http://www.loc.gov/preservation/scientists/projects/fidelity.html
http://www.loc.gov/preservation/scientists/projects/sticky_shed.html
that reference the work that Lambertus van Zelst reported on in March 2008
From the second link, some conclusions:
* Sticky shed results from the degradation of the binder that holds
the magnetic particles to the base tape.
* While storage at lower temperatures should increase tape lifespan,
and lower humidity will decrease the rate of degradation that
produces sticktion, PEU binders appear inherently instable. Magnetic
tape made with such binders must be assumed to have a finite lifespan.
* Several remedial techniques enable playback of "sticky" tapes, but
none stabilizes the material. Storage conditions may impact
recurrence speed, but sticky tape damage is irreversible and
reformatting should be given high priority. This does not negate
arguments in favor of retaining damaged masters in stringently
controlled low temperature and humidity storage, in anticipation of
future improved reformatting options.
* Among common remedial treatments, baking and dry cleaning have
advantages and disadvantages.
* Attenuated reflection Fourier transform infrared spectroscopy
(ATR-FTIR) may meet the pressing need in audiovisual archives for a
relatively fast, simple, and non-destructive diagnostic to identify
sticky shed syndrome before playback. Further research is needed to
demonstrate the utility of the method of a sampling of sticky tape
in a wide range of manufacturers and formulations.
Van Zelst's bio is here (in 2005--I guess he worked on this 2005-2008)
http://www.loc.gov/preservation/outreach/visit/
It looks as if Bert's paper was never published. I did spend some time
with him on it. I wish the paper could be released.
I see there is a new paper out by S. Hobaica in the Journal of Applied
Polymer Science in 2012. I'm trying to get a copy and I think it quotes
van Zelst's paper as unpublished.
This Google Scholar link provides a good cross section of the literature.
http://scholar.google.ca/scholar?q=related:ej6fSKJU-ycJ:scholar.google.com/&hl=en&as_sdt=0,5&as_vis=1
So, short of some revelation in the Hobaica paper, I still think that
all the govt's research and all the kings men will not help us do more
than we're doing now. As Ric said early on: "Copy it and give the
original tape Last Rites." We don't do that in audio, but you get the
idea. Ric essentially thinks we are on a fools errand (my paraphrase) to
try and preserve this degrading glue. This approach may be a boon to
Jamie Howarth if archives start to require "Mechanical Metadata".
Cheers,
Richard
On 2013-04-04 7:04 PM, Tom Fine wrote:
> Hi Sarah:
>
> Your explainations are the clearest I've seen so far. Thank you!
>
> I agree with you, some science needs to be applied to tapes as they
> age. I'm wondering if it's possible to gauge amounts of degradation,
> can a scale be established? Then, can it be determined if a tape
> farther along the degradation scale will always need a longer baking
> time? Or is something else going on?
>
> In any case, it would be very helpful just to establish a means of
> measuring degradation and quantifying it. I have some known sticky
> tapes that have not been baked and some known sticky tapes that have
> been baked if someone needs samples for this research. I would assume
> this is a chemistry and/or physics project? To be honest, I'm
> surprised the P&E Wing of NARAS hasn't gone to the record companies
> and gotten money raised for this research. It has tremendous bearing
> on vaults and commercially valuable master tapes. If we can understand
> how the degradation works, what its timeline is likely to be, we can
> then study whether super-dry storage makes any difference.
>
> -- Tom Fine
>
> ----- Original Message ----- From: "Sarah Norris"
> <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Thursday, April 04, 2013 4:40 PM
> Subject: Re: [ARSCLIST] Sticky SHRED
>
>
> Hi, Tom (and list):
>
> Please find responses below:
>
>> Would you, for us non-scientists on the list, summarize Bradshaw's
> thinking and the opposing view(s)? Please try to keep it in the realm
> of what an English major or at least what a MLS major can comprehend.
>
> A more thorough description is in my post from April 2, but here's a
> very abbreviated summary:
>
> Bertram / Cuddihy's model says baking works because it repairs the glue
> that holds the media together.
>
> Bradshaw / Bhushan's model says baking works because it makes the media
> and other degraded fragments hold hands for awhile.
>
>> Do any of the theories you explored about what causes sticky-shed
> reveal why baking times would be increasing as the tapes get older?
>
> The models summarized above answer the question, "Why does baking work?"
> The question we're asking now is something closer to, "How are tapes
> aging?" I think the first question probably is relevant to the second
> question, but probably not in a direct, straight-line kind of way. It
> makes logical sense that longer required baking times indicate more
> advanced degradation. Is that really the case? Now might be a great
> time for a series of studies, one every few years, comparing required
> baking times with degraded binder in tape samples!
>
>
> Sarah Norris
> Conservator
> Texas State Library and Archives Commission
> phone: (512) 463-5446
> fax: (512) 463-5430
> e-mail: [log in to unmask]
>
--
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.
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