In a message dated 10/24/03 10:03:59 PM, [log in to unmask] writes:
<< It's a kick to encounter such stability of a 50+ year old synthetic product
that not too long ago, was regarded as inferior to ostensibly state of the
art counterparts made 25 years later! >>
Its a long and convoluted story and I don't know the actual chemistry
involved, but tape stock manufactured from the late 1970s up to the early 1990s
suffered from a particular form of degradation unknown to previous formulations.
Those tapes outperformed previous tape in most respects: except long-term
Engineers gradually discovered that the problem was related to long term
absorbtion of moisture, causing destabilization of the binding materials;
manifested during playback as tape squealing, oxide shedding, "sticktion" (a
combination of stickiness and friction).
A work around was devised: baking tapes at approximately 125 - 130 degrees F
for 10 hours or more. By forcing moisture out of the tape temporary
restabilization was achieved. If tape is subsequently stored in low moisture or
moisture free environment, stabilization could be maintained.
Once this became common knowlege, even the tape manufacturers got involved in
the research into this. Its been estabished that above about 140 degrees F
magnetic flux is affected, otherwise, little or no damage is caused to the tape
itself or even plastic reels.
Numerous articles have been published since the early or mid-1990s, and may
be found in professional journals. A cursory search of Google keywords: "baking
magnetic tape" will yield a dozen such articles, including some by esteemed
members of this list like Graham Newton.