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Re: [ARSCLIST] TAPE resources online
At 11:00 PM 2007-08-16, Malcolm Rockwell wrote:
Has the possibility that the winding contact between the two
emulsions - front and back coats - is the cause of the syndrome?
That it is really the interaction of the two emulsions? If this were
the case then removing the backcoating should halt any further
degradation, once the tape has been baked, that is.
Hello, Malcolm,
This theory has intrigued me, but it seems the closest it comes is
that the long polymer chains break down with moisture (and the
inherent instability of the polyester polyurethanes that were used)
and then the mag coat and the back coat inter-twine the short chains
to some extent. The back coat has more binder (is "binder rich") and
the carbon black doesn't form any structure unlike the acicular
(needle-like) mag particles on the mag coat. So, there is more stuff
to degrade on the back coat.
We all agree that back-coated tapes behave worse, but Richardson
appears to be out there alone saying that the back coat is the cause.
I've discussed this at some length with the best tape chemist I know,
Dr. Richard Bradshaw of IBM (note all the credits in my recent paper)
-- I owe him a lot, and I am paraphrasing what he has told me.
Bradshaw was the one who figured out how to unwind the CHALLENGER
tape after the Navy scooped it off the ocean floor.
Baking and transfer still makes the best sense to me, though. Then
tossing the original master.
I remember hearing - back in the early 80s - that Ampex 456 would
begin absorbing moisture from the air immediately upon opening the
plastic bag around the reel. Then again, I have actually seen the
syndrome in full force upon opening the bag after boxes of tape had
been stored unopened for a few years.
Right--the plastic used for the bags is not an absolute water
barrier. In fact, the PET used for the tape basefilm is also
hydroscopic -- so it brings water around to the back of the coatings
as well! Only metallic foil is truly a moisture barrier at the levels
we're talking about.
This was disappointing, to say the least. Especially with the
expensive 2" stock! Couldn't even sell the stuff unopened.
Disappointing yes, but better to be rid of it without some precious
recording entrusted to it!
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.