RE: [AV Media Matters] Regular winding/rewinding of tape and film

[rohre@arlut.utexas.edu]

Jim is quite correct that I did not touch the topic of all CD/DVD potential
problems.  And some of the cartridge tape drive computer back up machines
suffer if a user carries around the removeable cartridge in our hot southwest
conditions.  Errors and inability to reread the cart are experienced by the
students who use one cart for a semester's work in a lab course.

And I did not mean to imply the chemical make up of audio and instrumentation
tape and others were the same.  What I think both Jim and I are saying is to
carefully handle all tape formats and all plastic media.  Most media do best
cool and dry for storage.  Careful handling of all media, including care in
picking where to store them, is like gently handling a very old book.

Tapes of various types are similar in that all have a base film, and an
information containing coating.  The coating for audio is tailored to those
needs while the particles on wide bandwidth Instrumentation tapes, or PCM
tapes are tailored in size to those requirements. There are other parts to the
tape including binders for the oxides, and back coating for the reasons Jim
mentions.

I am not sure if there ever were any metal ribbon magnetic "tapes" which would
of course not need a coating if the base was of magnetic material, but of
course there were magnetic wire recordings up until the end of WW2 and the
growth of first paper and then plastic based magnetically coated tapes.
Original Flight data recorders used a stylus marking a metal foil tape, but
that was not a magnetic recording.

There was archival use of Kapton base film for high temperature rated magnetic
recording 9 track computer tape by Graham, but more recently, Kapton as used
in wire insulation in aircraft has been found to crack over the years, and
then to ignite explosively if heated too high.  I think this might be why
Kapton film went away as a archival tape base film.  I am not sure what the
maker thought the user was going to do if the tape was in a fire.  Surely it
would reach the Curie point temperature which could have erased the recording,
making survival of the base film not much of an advantage.

Back coatings apparently are changed even on tapes of a certain model no.
Does anyone know when or why Quantegy, (formerly Ampex) changed the
backcoating on type 722 PCM tape?  The fact that the backcoat has changed
appearance on recent versions of this tape, and is almost the same color as
the oxide side was pointed out to me just today by a user of this tape.
Formerly he said, the backcoating resembled tapes such as 799, or 79L.