Bad Tapes. 1 bit of info...

From: John Lawson <jpl15_at_panix.com>
Date: Mon Apr 26 14:53:33 2004

  This is turning into an Urban Legend as we watch - or, as was once quite
succinctly put: "The plural of anecdote is 'bullshit'". ;}


 Some older formulations of tape - notably Ampex Grand Master 456 - has
proved unstable over time. Recording tape of all kinds consists of a
plastic strip, called the backing, made of various type of plastic -
cellulose nitrate, acetates, or polyesters generally - with some
formulation of a ferrous powder applied to it. The powder is very finely
divided iron oxide, crystalized microscopic metal particles (acicles), or
verious magnetic alloys - all reduced to a very fine dust.

  This dust is mixed with emulsifiers and lubricants, as well as an
adhesive (the binder) to keep it stuck to the surface of the backing.

  There are two main modes of [chemical] tape filure - either the backing
fails, as when acetate tape decomposes and the acetic acid coalesces out -
giving some old tapes that 'vinegar' smell, or other failures of the
backing chemistry to cause it to break, warp, or disintegrate. OR - the
binders fail and the oxide layer becomes disassociated from the backing
altogether (flaking or peeling), or the binder adhesives begin to 'weep'
out of the oxide, and then it gets the whole tape path gooey and
everything comes to a viscid halt in short order.

  In cases where the binders are failing - it is possible to try and dry
the media in an oven - very low humidity and about 120 - 150 degress F for
a few hours. Then it can hopefully be played back and the program
recovered. I've had mixed luck over the last 20 years of direct
involvment in audio and media restoration of all types. I've had some
impossible-to-play tapes return completely from the dead - and I've had
reels that had fused into a sorry, solid block of gooey ruin...

  These failures are much less common with data cassetes and 1/2" computer
tape, because the formulations and speeds, etc, are different.

  Nonetheless, baking media is sometimes quite effective - but it's best
if you know pretty much *why* you're doing it in the first place - and
also it's good to have a firm idea of exactly what the next step after
baking is going to be - because you won't have much time to try and
recover your data after that.


   Cheers

John
Received on Mon Apr 26 2004 - 14:53:33 BST