Dear All, Here at the British Library National Sound Archive we have found a
total of six double-play and triple-play Agfa tapes showing similar
symptoms. The oxide adheres to the backing of the next layer, which in this
case is glossy (not matt). At normal playing-speeds (7 1/2 ips) the oxide is
completely wrecked in the process, and the tape ruined. Neighbouring tapes
in the same collections are usually OK, it afflicts (I would guess) one tape
in five hundred. We are currently using outhoused contractors to get the
sound off such tapes for print-through reasons. The contractors are all
mandated to unpeel the outer turn of the tape very slowly, and if the oxide
shows signs of coming off, return them to us unplayed.
You cannot bake such a tape; as Richard Hess says, it's different from
the usual synthetic polyurethane binder problem. Following an accidental
discovery on my part, the solution seems to unwind the tape incredibly
slowly. I understand that what we call "Sellotape" here in England is
conversationally called "Scotch Tape" in America. If you pull some Scotch
Tape from the reel fast, it goes "pzzzzip" as it separates, while if you
pull it slowly it separates cleanly. We have built a prototype machine
(called a "Grandfather Clock", because that's what it looks like) to unwind
the tape incredibly slowly. The gearbox ratio can be changed, but at the
moment the takeup reel turns at one revolution a minute, so a reel may take
three days to unwind. As this happens, it travels up the grandfather clock
through a box fed with warm air from a fan to dry it before it reaches the
takeup reel. But until last week, we hadn't enough examples of such tapes to
test the machine thoroughly. I hope to present the resulting design at the
ARSC/IASA conference in London in September.
Peter Copeland
<peter.copeland@xxxxx>
-----Original Message-----
From: Richard L. Hess [mailto:lists@xxxxxxxxxxxxxxx]
Sent: 20 April 2001 07:28
To: AV-Media-Matters@xxxxxxxxxx; arsclist
Subject: arsclist Scotch 176 adhesion problems
I hope this cross-post isn't too annoying.
I dug out a 1976 reel of Scotch 176--or at least that was what the box
says. I was going to transfer it to DAT (and ultimately to CD-R). I started
playing it and I saw layer-to-layer adhesion. It's not sticky shed. There
is no residue on guides, but rather some of the oxide may be attaching
itself to the back of the tape. I stopped playing as soon as I noticed (it
didn't happen for the first ten minutes of the tape). There are a LOT of
splices in the tape so it may not be a homogenous type.
I've not seen this before nor come across it in my reading.
Is it sticky shed? Is this a bakable disease? Will baking hurt?
It is not a back-coated tape and it appears to be 1.5 mil...so there is a
good chance it is mostly 176. I guess by 1976 CBC had switched to this?
Could there be Racal Zonal mixed in? Since the first few cuts didn't
exhibit this and about the tenth little skit in (there might be 40 on this
reel) exhibited what I have described. Although some Zonal from 1973 did
well for me two years ago.
The products of the adhesion are splotchy towards the center of the tape.
I'm not sure how the tape was stored, but I suspect in a humid basement for
a long time. Could it be mold? I've had it about a year and am only getting
to it now, so the nose test won't be as useful as a year ago. Most of the
stuff coming out of that basement in Toronto was damp--some downright wet.
I had to replace a box which had gotten so wet that it was all buckled, and
coming apart...but I don't think it was for this reel since this 176 box
has what appears to be the correct label on it. It is very poorly wound
with lots of edges out.
Any thoughts would be of great use.
I check the lists in the evening, but if you could reply to
richard@xxxxxxxxxxxxxxx I'll get it sooner during the day.
Thanks!
Richard
Richard L. Hess richard@xxxxxxxxxxxxxxx
Glendale, CA USA http://www.richardhess.com/
Web page: folk and church music, photography, and
broadcast engineering
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