tape baking

[Chuck Guzis]

I'm a bit surprised that this is even a "thing" in the audio business.
Restorers have been baking audio tapes for a long time.

One thing not discussed (maybe it doesn't occur in audio) is that there
can be issues in binder formulation, at least in digital tapes.  In
particular, 3M tapes, most notably Scotch 701 and 777 formulations, have
an issue where the binder "liquefies" under motion and solidifies when
tape motion slows or ceases.  So, you may be running a tape through a
drive just fine and then suddenly, everything freezes up as the tape
becomes firmly "glued" to the heads or other objects in the tape path,
usually with a loud squeal.

In the current batch of 60 tapes from the late 60s-mid 70s, every single
3M tape exhibited this behavior.  It didn't matter if they'd been baked
or not.  There was a note of this on Ed Thelen's site where someone had
encountered this and given up.

Isopropanol does not clean the sticky deposits from equipment--you must
use a stronger solvent.  Acetone, Perc or MEK generally does the trick.

Rather than try to clean the gunk off the tape, which is probably a
fool's errand, I coat the tape with cyclomethicone, using a felt
applicator in my cleaning machine--it doesn't take much to create a
slippery film on the tape surface, perhaps 10 ml will do a 2400' tape.
Cylcomethicone is non-toxic and relatively inert--and is somewhat
volatile, so that it evaporates in a couple of hours, leaving the tape
as it was.  Very slippery stuff, so don't spill it on the floor!  It
does not appear to have a solvent effect on the binder, as nearly as I
can tell.  It also doesn't appear to bother the equipment either.

I've achieved 100% success using this method.

I think it's interesting that tape quality tends to better the older the
tape.  Audio Devices, Ampex and IBM Series 500 tapes tend to survive the
best. Memorex seems to get worse, the younger it is.  (e.g. MRX III
tends to behave better than MRX V).

For whatever it's worth,
Chuck