Charles:
While working on the AES and ANSI technical commissions on magnetic
tape
stability, we reviewed large numbers of documents from both private
and
government labs from around the world (US, Canada, Japan,
Germany ..., 3m,
Agfa, Sony...) and we were never able to locate any repeatable
laboratory
testing that proved a signal deterioration associated with multiple
baking
of a tape. There were anecdotal reports of such but no laboratory
testing
to back up the anecdotes. If you actually have quantifiable
laboratory
results to back up a loss of signal that can be specifically
attributed to
baking of a tape (and contains sufficient controls in the testing
protocols
to isolate the baking as the cause), I would love to see the results
of the
testing. As I said, we looked for such a study and were never able to
locate one. We found lots of other interesting results but not this
one, in
specific.
Peter Brothers
SPECS BROS., LLC
973-777-5055
peter@xxxxxxxxxxxxx
Tape restoration and disaster recovery since 1983
-----Original Message-----
From: Association for Recorded Sound Discussion List
[mailto:ARSCLIST@xxxxxxx] On Behalf Of Charles A. Richardson
Sent: Saturday, April 05, 2008 10:27 AM
To: ARSCLIST@xxxxxxxxxxxx
Subject: Re: [ARSCLIST] Fwd: Sticky AGFA PEM 469
Dear Tom: What Claus describes with Ampex sticky tapes is exactly my
experience -- they go sticky again after about 30 days. What Claus
did not touch on but has definitely been my experience is that there
is audible deterioration after two or three bakings. Treble dropoff,
fuzzy upper midrange, the kind of stuff you hear in multi-track if
it's been run thru too many times for endless punch -ins.
I have spent the last 10 years researching the causes of such tape
problems. My own research, as well as the research of a well-regarded
forensic chemical laboratory which I engaged to find and explain these
complex chemical issues, confirms that the new remediation method that
I devised is very effective and restores the tape to excellent sonic
and mechanical performance. Although my research continued and
provides more information today, the paper I presented at AES in 2006
in San Francisco provides an explanation and drawings for both these
mysteries, namely why the tape becomes sticky again after baking, and
why sticky tapes have increasing high frequency losses and drop outs.
If you contact me off list, I would be glad to send you a copy of my
paper (and a newer follow-up paper) for your review and comment. In
addition I am working on new papers (and a prototype machine to
mechanize my process) which will soon be released.
Charles A. Richardson
Richardson Magnetic Tape Restoration
1938 Baltimore Annapolis Boulevard
Annapolis, MD 21409--6248
410-757-3733
On Apr 2, 2008, at 8:20 PM, Tom Fine wrote:
Hi Goran:
Thanks for digging these posts up.
What Claus describes with Ampex sticky tapes is exactly my
experience -- they go sticky again after about 30 days. What Claus
did not touch on but has definitely been my experience is that there
is audible deterioration after two or three bakings. Treble dropoff,
fuzzy upper midrange, the kind of stuff you hear in a multi-track if
it's been run thru too many times for endless punch-ins.
I have also had experience with some Ampex tapes so badly stuck
together that even baking would not make them un-spool correctly.
The oxide would be "glued" to the back-coat of the layer ahead of it
and thus would rip the back-coat off and end up an unplayable mess.
This was with tapes that had been under extreme storage conditions
(basements, attics, garages).
As for 3M, I can say that Scotch 226 and 227 reels I've had the
misfortune of dealing with behave pretty much like Ampex tapes. I've
never seen this white film discussed in the old posts, just typical
sticky-shed that is temporarily cured by baking. However, with 1-mil
Scotch 227, I had to bake 18 hours and let cool 18 hours to make one
pair of 3600' reels fully playable with no shedding. These
particular reels happened to go back sticky within 2 weeks, because
I tried to make another go at part of one and ended up with quickly
discovering it was sticking and needed another baking. Luckily, the
second pass worked great and those reels were disposed of later on.
I have a bunch of Agfa PEM 468 1/2" reels recently given to me. I
will report back if I run into any troubles. The two I've played so
far are just fine, and one was literally in a basement closet for at
least a decade.
-- Tom Fine
----- Original Message ----- From: "Goran Finnberg" <mastering@xxxxxxxxx
To: <ARSCLIST@xxxxxxxxxxxxxxxx>
Sent: Wednesday, April 02, 2008 11:11 AM
Subject: Re: [ARSCLIST] Fwd: Sticky AGFA PEM 469
Peter Brothers:
The microwave process is called the XT process. It is patented,
That´s correct.
I have saved this from the ARSC list in 2004 that gave some more
information coming directly from Terry O´Kelly of BASF:
-----------------------------------------
ctrelby@xxxxxxxxxxxxxxx 9/28/2004 5:06:38 PM >>>
Hi John,
Welcome to the 70's tape pit. I'm sure you have heard about sticky-
shed
syndrome etc.
Environmental law changes forced most tape manufactures to change
the
formula of their binder in the early 70's. This has left us with
resulting
sticky-shed and other artifacts. Scotch/3M I have found not to
exhibit
sticky-shed unless it was stored VERY poorly, but* A fine white
powder
will
in many cases be released and distribute itself on the tape path and
heads.
It is very hard to see, and in many cases you have to look at the
erase
head
(it's black) to see this. The powder is fine enough that it will
slowly
deteriorate the Hi frequency play-back response during a pass.
The baking of tapes is not a fix-all solution. It was specifically
developed
by a group of engineers from Ampex to solve the sticky-shed issues.
AGFA
developed their own solution to the same problem. (I'll include an
email
from a BASF engineer to our Video Director at the end of this
posting).
No
such study was done by Scotch/3M to my knowledge but I have found
that a
pass or two on a pellon based cleaning machine with light tension
will
clear
off the powder and render the tape playable. This process can also
be
done
by hand if you are very careful.
I know this doesn't answer your question about TDK, but I have not
encountered tapes from the 70's from TDK, and have no direct
solution
for
you. It sounds like and cleaning pass is in order for you, BUT
PROCEED
WITH
CAUTION, and test on lengths of tape with no audio, since you might
damage
the tape in trying to find your solution.
The following excerpt is from and email from Terry O'Kelly,
formerly of
BASF
to Pat Shevlin, Xepa Digital. (130 @ 8hrs refers to 10.5" dia, 2"
tape -
I
would still suggest this process is done by engineers with
experience to
assure a successful result)*
...
"I do have good records of the Agfa XT process and the AMPEX
process for
driving water molecules out of the polyurethane binder. Agfa used a
microwave, but the oven had to be so carefully controlled over a
short
period of time that it was not generally recommended for users.
IDT in
West
Palm Beach licensed the Afga method, but I don't know if they are
still
around.
The Ampex method used a convection oven with an internal fan that
moved
heated air around the tape. The tape was slowly brought to a
temperature of
130 degrees F. for a period of about 8 hours. Plastic reels could
be
used,
but it was better to have transferred the tape to a metal reel. The
transfer process itself helps to redistribute tension in the tape
pack
to
make it more uniform. More than one tape required a spacer such as
an
empty
metal reel. Once the tapes had cooled to the touch, they were good
for
about 30 days; but copying the data as soon as possible was
safest. The
binder would begin to absorb water again after 30 days, but the
linking
structure of the binder would be damaged enough that a second
baking may
not
have prevented the oxide/binder combination from delaminating or
rubbing
off
altogether.
The goals of both the Ampex and Agfa methods were the same: drive
the
water
molecules out. The XT process was faster but more difficult
without a
very
controlled environment. The Ampex process was slower but easy to
follow
for
most people."
...
I hope you find this helpful.
Claus.
Claus Trelby
Managing Engineer/Partner
XEPA Digital
1137 Branchton Road, 19-N-3
Boyers, PA 16020-0137
www.xepadigital.com
ctrelby@xxxxxxxxxxxxxxx
P:724-794-3686
F:724-794-3292
C:805-490-1730
--------------------------------------------------------------
--
Best,
Goran Finnberg
The Mastering Room AB
Goteborg
Sweden
E-mail: mastering@xxxxxxxxx
Learn from the mistakes of others, you can never live long enough to
make them all yourself. - John Luther