Re: RE: [AV Media Matters] Newbie to list question - tape baking,

[Jim Wheeler <Jimwheeler@aol.com>]

Ampex also trademarked the name "videotape".  Ampex patent attorneys have a
little trouble with the follow through.  I can talk for hours about the
incompetence of Ampex patent attorneys.

I was involved in developing the tape baking at Ampex and was shocked to
learn that Des Maderas got a patent for it.

Our work at Ampex was with both video and audio tapes.  I was first made
aware of the "sticky-shed" problem by Richard Warren at Yale.  I visited
Richard along with the Ampex Tape Rep--George Laforgia.  Richard showed us
how an Ampex tape coated the heads on an audio machine and caused squealing.
Fortunately, Richard had a case of the same tape that he had never opened.
This case was taken back to Redwood City where we tested the tapes and came
up with the baking technique.

The tests at Ampex were made on several tapes from several sources.  We
found
that baking made tapes playable many times for a period of a few weeks and
for several months in a few cases.  Rebaking made them all playable again.
We
 rebaked some over a period of three years and they were always playable.

I never proved it but I am convinced that it is the low humidity that is
restoring the tape to a usable form.

The sticky-shed means that the binder is breaking down but the baking (low
humidity) is reversing the hydrolysis.  My personal opinion is that the tape
still has a long life IF it is stored in a cool and dry environment.  By
dry,
I mean below 30 RH.  Cool is anything below about 20 C/70 F.

Testing at the Australia National Library indicates that the only problem
with baking audio tapes at 120 F is about a one db loss at high frequency.
For voice tapes, there is no problem.  As Steve Smolian points out, there is
a potential problem with increasing print-through.  I haven't had noticable
print-through problems below 120 F but it is certainly a possibility.
Winding the tape back and forth a couple of times should eliminate any
print-through problem.

Jim Lindner's problem with tracking on video tapes is probably due to the
stre
sses in the pack caused by starts and stops during previous playbacks.  The
good news is that the polyester can have its "memory" changed.  I have done
this by running the tape end-to-end a couple of times at high speed followed
by a second baking.  The pack stresses were "neutralized" by the high-speed
winding and the second baking gave the tape a new tension profile.  The
"normal" tension profile is nominal in the middle 80-90 percent and high at
both ends.

I have baked hundreds of tapes and have never had any bad results.  I bake
at
115 F in a Blue M that I bought second-hand for $400.  I have also used a
$300 Real Goods fruit dehyrator (with a fan) with good results.  In both
cases, I monitor the temperature and humidity with a chart recorder.  I ramp
up the temperature over a couple of hours, stay at 115 for about 20 hours
and
then ramp down.  I don't know if the ramping is necessary.

Baking only works for polyester tapes.  Diacetate audio tapes from the 50s
and early 60s have a totally different problem--Vinegar Syndrome!  You can
determine what the basefilm is by pulling on the first inch or two of the
tape.  If it breaks clean, it is diacetate.  If it stretches, it is
polyester.  If you smell vinegar, you had better copy it soon.  The acetic
acid causes the tape to deteriorate fast.

Jim Wheeler

P.S.  It took Richard Warren and Ed Cuddihy (JPL) to make tape life an
issue.
 Until I read Ed's article and saw Richard's problem, I was not aware of a
tape life problem.  Richard made the problem known to the Archival community
and Ed made it known to the Scientific community.

P.S.-2  Quantegy no longer bakes tapes.  The chief baker retired.