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Re: [ARSCLIST] revisiting tape bakers
Hello, Charles,
It is interesting that you should post all of these comments. I would
like to suggest that your understanding of this condition and my
understanding of this condition are somewhat different.
Your authority is a nationally recognized forensic laboratory. One of
my authorities is Dr. Richard Bradshaw formerly of IBM who, among
other things, unwound the Challenger instrumentation tape after it
had been on the sea floor while other experts said it couldn't be
done. Bradshaw and his lab in Tucson were responsible for much of the
basic science into understanding the fundamentals of tape chemistry,
physics, tribology, and life. Bradshaw's former colleague, Bharat
Bhushan wrote several books on the subject.
For those of you who wish to read Dr. Bradshaw's perspective on this
particular project, please jump to the end of this over-long message.
At 01:00 PM 2008-11-07, Charles A. Richardson wrote:
Hi Richard:
There has been a continuing discussion of baking as a remedy for
sticky shed contamination on magnetic tapes. List members point to
the Ampex Baking Patent as authority for baking sticky shed tapes to
enable playback. The discussion seems to assume the safety or ignore
the damage that baking does to tapes. Baking is dangerous and much of
the information about baking tapes is misleading. The following is
not just my opinion or assertion but has been substantiated by the
scientific analysis of a nationally recognized, independent forensic
chemical laboratory.
1) The baking process set out in the Ampex Patent melts the sticky
shed debris with heat energy. This stops tape
frictional squealing while the sticky shed debris remains in a
liquefied state, but the squealing returns after the debris cools off
and solidifies once more. It does not cure the underlying chemical
causes of the tape problems which return endlessly.
What is your evidence for this? The Bertram and Cuddihy 1982 paper on
"Humid Aging..." does describe the scission process fairly well. I
think both of us find fault with the claim that the scission process
of the bonds is a reversible process. While it may look fine on
paper, Bradshaw assures me that it just doesn't happen that way in a
filled matrix.
The melting that I mention in my paper is related to the
pre-treatment state of the tape and the conjecture that localized
heating causes the melting of the sticky shed deposits to the tape
heads and guides which is why these deposits are difficult to remove.
Brown (1980) reinforces the humidity-driven breakdown in
polyester-polyurethane systems.
2) Magnetic tapes are made with complex chains of polymers. The
polymer links are extremely heat sensitive. Baking destroys the
flexibility of the tape and the binder adhesion because it damages the
links in the chemical chains. Applying heat permanently breaks down
the chain links, causes unwanted new cross linking of chemical bond
links, and creates new, unwanted chemical compounds. The tape becomes
increasingly brittle and the coatings start to flake off the base
film. Repetitive baking increases the damage to the chemical,
magnetic and physical components, and eventually destroys the tape.
Actually, Brown shows that the polyester polyurethane chains are not
substantially heat sensitive but rather humidity sensitive. While the
heat applied to the tape may be above the glass transition
temperature of the binder system (especially in degraded binders
where the loss of that temperature is a symptom of the breakdown of
the binder system) it is NOT particularly close to the glass
transition temperature of the base film.
In the hundreds of tapes that have been baked, we see a hardening of
the mag coat and an apparent increase in the glass transition
temperature as the heating drives out some of the moisture that has
been retained within the mag coat matrix.
If there is re-cross-linking it is wanted, not unwanted, as that
increases the robustness of the mag coat and allows us to obtain
additional playback.
It appears that normal degradation of the tape and/or incomplete
reactions during original manufacturing is already producing these
unwanted compounds. They are already in the tape prior to baking.
As to baking damaging the magnetic characteristics, I believe we are
well below the curie temperature of the magnetic particles, so I do
not think that is an issue. I agree that multiple baking is to be
avoided, but also have successfully baked some master tapes twice.
The descriptions provided in paragraph two sound much more like
describing a tape baked at temperatures far above the recommended
temperatures in the Ampex patent or perhaps baking an acetate based
tape which is outside the scope of the Ampex patent. Baking has been
contraindicated for acetate tapes since day one.
3) Sticky shed debris, liquefied by baking, collects at the tape head
gap. This debris accumulation pushes the tape oxide surface further
and further away from the tape head's surface at the critically
important head gap. This collection of debris causes a physical and
major magnetic separation loss, which, as you know, severely reduces
the ability of the tape head gap to magnetically scan the short wave
lengths of the oxide's recorded content at high frequencies. This
results in inferior mechanical, magnetic and sonic playback
performance and thereby a deficient transfer of tape content. The
playback head's high frequencies are greatly reduced, the noise
reduction system playback performance mis-tracks, and worsens these
high frequency losses. Thus the tape sound quality is now made dull
and lifeless because sticky shed debris on the head gap magnetically
attenuates proper and complete scanning of the important high
frequencies that are now greatly reduced or even missing altogether.
Your description of spacing loss and its increase, starting with the
second sentence is correct and in my experience precisely correct
when attempting to play a tape which has not been baked but needs to
be. My only change is that I would use the term "wavelength" as
opposed to "frequency" as the spacing loss is related to the
wavelength which, as you know, is a function of speed and frequency.
As to the first sentence, the sticky shed debris is not liquefied by
baking which is why a cool-down period (if not in the Ampex patent)
is recommended by all proponents of baking. In addition to the Ampex
patent, 3M also has recommended similar procedures but with a greater
stress on the cool-down period.
In fact, I do agree with you, playing the tape warm right out of the
baking process is not a good idea. If the baking is done properly
(i.e. long enough at the proper temperature) there is no debris
accumulation upon playback of the treated tape.
4) Baking causes increased print-through.
I will agree with that in some circumstances, although measuring it
in a controlled environment is difficult if not impossible.
Print-through ready exists on most tapes anyway and is a function of
the different range of sensitivity to magnetization of individual
particles. The most sensitive particles are the ones that can become
remagnetized and are the target for the "skimming" function that
Studer provided in the later versions of the A820 mastering recorder
(which I do not have) that can "erase" the print through.
I will further suggest that some of the "print through" that has
become audible on improperly handled tapes subject to sticky shed
syndrome is actually binder pullouts from the mag coat bonding with
the back coat and being heard through the tape. In many cases of
advanced sticky-shed syndrome (SSS), the back-coat-to-mag-coat
adhesion is very strong resulting in substantial pullouts of the mag
coat. This is why we never wind SSS off of the reels they are
supplied on but bake them as found. Note that this includes plastic
reels. If the baking parameters are set properly, most plastic reels
will not deform.
5) Baking causes weakened magnetic fields and thus lower flux and
output signal levels.
The only study I am aware of that mentions anything in this regard is
the one done by the Australian National Archive and shows perhaps a
0.25 dB loss at the shortest wavelengths. It was definitely frequency
dependent, but well under one decibel which is well within the
tolerances of a reel of tape end-to-end. See comments above about
curie temperature.
6) Baking does not provide any "restoration" or "rejuvenation" of
binder chemicals. To the contrary, it causes progressive
and permanent damage to and destruction of the tape. A fundamental
thermal law of chemistry is that heat energy destroys
substances.
Yes, and I believe the when we calculate the relative damage caused
by different temperatures the equations use kelvins not degrees
celsius. I have been told that if one does the math, that a single
baking cycle would take weeks off the life of the tape. There is heat
energy at room temperature. There is heat energy in the refrigerator.
There is no heat energy at absolute zero.
Baking simply allows us to obtain an excellent transfer today. We
have the technology to arbitrarily record this transfer in any format
that we wish. We need to rescue the contents from the unstable
ribbons we call magnetic tape. Magnetic tape is not a permanent
storage medium. Nothing is. The attraction of digital is that there
is no penalty for migration from one storage bucket to another. There
is a loss in each generation in copying analog materials, but the
choice is the users: copy to digital or analog, but get the content
off the decaying old tape.
As Bob Perry, (former Director of Advanced Development in the
Magnetic Tape Division of Ampex) said in a phone interview in July
2006, "If I wanted to keep it, I'd copy it if the tape was more than
10-15-years-old."
7) Baking is not a safely repeatable solution. Each time a tape is
baked, it requires higher temperatures and/or longer bake times. Each
round of baking produces worse chemical, physical, magnetic,
mechanical, and sonic results.
I have done it twice and the second transfer sounded better than the
first because I had obtained a superior reproducer. No...the
temperatures should NOT be increased past the highest in the Ampex
patent. Results from higher temperature baking cannot be used to
assess the damage of Ampex-patent temperature baking.
8) The high heat used in baking drives off by evaporation the light
weight polymers and causes the magnetic particle material attached to
them to fall off.
And where do these magnetic particles go? I don't see them coming out
the vent. I don't see them in a pile in the baker. I don't see them
under the tape or around/on the heads and guides. We're talking about
rust particles here, they just don't evaporate into thin air.
9) Baking the tape damages the tape's magnetic content and seriously
degrades the playback performance. People have ruined tapes by baking
them, but this is generally not admitted, possibly because of fear of
liability and potential loss of income. They may be unaware of any
other method to stop tape squealing safely and permanently.
Yes, many tapes have been ruined by improper treatments of all kinds.
I attempt in my forthcoming ARSC paper (an updated version of the AES
paper where we shared the dais) to detail most of the known treatment
methods. I attempt to differentiate between tapes that are suffering
from SSS and squealing tapes that are not suffering from SSS. I see
SSS as a subset of soft binder syndrome. In this paper, I provide
details on my cold playback technique which has been validated by
several other researchers. Its application appears limited, but
allows playback of certain tapes that squeal at room temperature. My
publication of this will hopefully be adequate as "prior art" if
anyone attempts to patent the technique. If this technique helps
restore a few tapes, then I will be happy to have promulgated it.
10) Some proponents of baking try to rationalize this dangerous
baking method by inventing a new set of terminology and
circumstances, such as "soft binder syndrome", to justify using the
baking technique to obtain a mediocre playback. I am unaware of any
scientific evidence or support by an independent laboratory for "soft
binder syndrome" as either being separate and distinct from or a
sub- set of sticky shed syndrome.
That would be me. Prior to my introduction of the term Soft Binder
Syndrome (SBS) a lot of people were discussing Loss of Lubricant
(LoL). The classic tapes that were called LoL (3M 175 and Sony
PR-150) showed up in analyses to have the lubricant (~molecular
weight 500) components still in the mix, but to have a lowered glass
transition temperature (a symptom).
The taxonomy for SSS is that if it responds well to baking (as many
of the Ampex and some of the 3M tapes do) -- and I believe these
tapes are all based on varieties of BF Goodrich (at the time) Estane
polyester polyurethane binders, although similar products from other
manufacturers could have been used -- then it is SSS. If it does not
respond to baking then it is generic SBS. A subset of SBS tapes
respond to cold playback.
11) The accurate standardized chemical terminology is that tape
binders are inherently hygroscopic, and thus are susceptible to
hydrolysis. The only safe and highly effective method to restore and
preserve tapes suffering from hydrolysis of the binders, or sticky
shed syndrome, is to first, put the affected tapes in a stable
environment of low heat and humidity for as long as it takes to
reverse the hydrolysis reaction, and then second, safely clean all
the tape's debris from both the oxide surface without damaging the
surface, and also completely remove its chemical material causal
source, namely the deteriorated carbon black back coating.
The patented Resurex(tm) process! I am glad that this process now
includes the cold/dry soak as that will often (over a period of many
months) perform the required moisture removal that baking does in a
day. It is important to stabilize the binders as much as possible
before attempting separation of the back coat and the mag coat as
described above.
Since the mag coat and back coat may share the same binder chemistry,
and pure elemental carbon tends to be quite stable, where is the
evidence that the back coating is the causal material.
What is interesting is the SBS tapes which work well in
low-temperature playback (a) do not shed like SSS tapes prior to
baking and (b) are not back coated to begin with.
Off the reel cold playback does not work for traditional SSS tapes.
Long-term DRY soak (not necessarily cold) has been shown to repair
some tapes that were suffering from too-high-humidity storage. It has
not been shown to restore SSS tapes in the information (other than
yours) that I have seen.
12) Much reliance has been placed, or should I say misplaced, on the
Ampex Baking Patent. The Ampex Baking Patent is intended solely to
expedite the transfer of recorded information. The title, "Restored
magnetic recording media and method of producing same", is inaccurate
because the baking method does not take steps to preserve the media,
but only to restore temporarily a "playable condition" in the media.
It is merely a band aide fix, not a cure.
And, since tapes in general do not violate the laws of entropy, no
tape is permanent.
13) The 1993 Ampex Baking Patent suggests that heating tapes to
120-130 degrees Fahrenheit "does not further deteriorate the tapes"
and implies that baking a tape for prolonged periods of time is safe.
The patent does not cite scientific or chemical evidence to back the
"no further deterioration claim". Moreover, the claim runs directly
contrary to pre-existing chemical thermal laws and 1980 scientific
findings that heat damages tape's magnetic content by increasing print
through levels, published in a scholarly article written by Ampex's
own staff scientist, H. Neal Bertram. "The Print Through
Phenomenon" (JAES Volume 28, Issue 10, pp.690-705; October 1980).
Bertram has, I belive, written three papers on print-through which I
am attempting to study but have not gotten through them completely.
Remember, the temperatures of the baking process are not higher than
short-term shipping excursions that can be expected. In fact, I would
suggest that operating environments even through room ambient is in
the mid-70sF might show 80-90 degrees above the reel motors and more
at the head assembly. The machine is the heat sink in many cases.
14) The elevated temperatures stated in the Ampex Baking Patent,
120-130 degrees, also violates Ampex's own tape manufacture's warranty
limiting heat to not exceed 90 degrees. This chemically abusive high
baking heat radically shortens tape lifespan to a small fraction of
the time tapes can last if they are instead stored and handled as
chemical science requires. Tapes have the ability to be reliably
archival for a very long time. However, if abused by improper
storage, handling, and wrong headed restoration, then tapes are
damaged, degraded, and destroyed far ahead of their time.
If tapes had the ability to be reliably archival for a very long time
we wouldn't be having this discussion. Some tapes have this ability,
but at least some tapes that are 50 years old or older are challenged
in one way or another.
15) As you know, a patent does not confer a certification or
implication that an invention is scientifically proven to be effective
or safe. A patent is a grant from the U. S. government (or other
authority in other countries) of a right to exclude others from
making, using, or selling one's invention and also includes the right
to license others to make, use or sell it.
A patent application is only narrowly and formally reviewed to
determine whether the invention is entitled to be granted a patent
under U. S. Patent law. The most important requirement under U. S.
Patent law is that the invention be a new or useful process, machine,
manufacture, or composition of matter, or any new and useful
improvement thereof. Clearly, a patent, baking or otherwise, is no
scientific authority and no certification of safety.
I am well aware of this and it applies to 3784746 and 6797072 as well.
16) Richardson Magnetic Tape Restoration is concerned, not just with
minimal baking type partial recovery of the magnetic content
information contained within a sticky tape, but with the long term
preservation of magnetic tapes as the primary or original source of
the all the magnetic content information on the tapes and to create
optimal playback conditions for high quality reproduction needs. To
achieve this goal, RMTR hired a nationally recognized independent
forensic chemical laboratory to test chemically and to examine under a
high power electron microscope, the sticky shed tapes, before and
after application of baking heat treatments. The lab results showed
significant deterioration of the tape after it was heated as per the
Ampex baking patent. Application of heat treatments, the chemists
concluded, accelerates even more damage from hydrolysis, and increases
the cross linking of the polymers used in making the PET Mylar base
film and binder components of the tapes. This baking practice soon
"leads to unwanted tape destruction." The chemists also concluded
that the new RMTR process was both safe and effective for tape
restoration, preservation, and playback mastering needs.
I have a written paper that elaborates on these concepts. The paper
is available on request.
If you or any other list members have independent chemical laboratory
research that refutes these points or supports baking as both safe and
effective for the restoration and preservation of magnetic tapes, I
would appreciate seeing it.
Suffice it to say that there are multiple tape restorers on this list
who are making EXCELLENT transfers after properly baking tapes.
When we last discussed this in April of this year on this list, I
forwarded your message at that time to Dr. Bradshaw who responded
privately to me -- with permission to use his quotes as I saw fit:
"Richardson's apparent conviction that his process would allow a tape
to then [be] archived forever is absolutely ridiculous..."
Cheers,
Richard
Richard L. Hess email: richard@xxxxxxxxxxxxxxx
Aurora, Ontario, Canada (905) 713 6733 1-877-TAPE-FIX
Detailed contact information: http://www.richardhess.com/tape/contact.htm
Quality tape transfers -- even from hard-to-play tapes.