I've done this successfully by putting a dampened- not wetted- paper towel
in a film can with the tape on a reel, being sure the towel does not come
into physical contact with the tape.  Do it on one side only.  If you do it
on both, you have no way of knowing if the center has been rehydrated. This
is slowly successful (days, not hours) but may also need repeated
applications to be sure the water vapor makes it through the middle to the
other side of the tape.

If the dry tape has been tightened, be sure to rewind and wind it again
after it is remoisturized to relieve the tape tension unevennesses that will
occur.  Being even more obsessive, I'd suggest letting it sit a week after
this rewind dance takes place to reduce any rippling effect as the tape
passes the heads.  This is of particular importance with stereo to avoid or,
at least, reduce phasing issues.

Steve Smolian

-----Original Message-----
From: Association for Recorded Sound Discussion List
[mailto:[log in to unmask]] On Behalf Of Don Tait
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Sent: Friday, December 09, 2011 3:42 PM
To: [log in to unmask]
Subject: [ARSCLIST] Fwd: [ARSCLIST] Treatment for Acetate Tapes

I agree with Scott Phillips. I'd like to read everyone's comments  about
this on the ARSC site if everyone is willing. Because I have some acetate
tapes from circa 1957 that are dried, curled, and that I want  to preserve. 
  I'll tell something that was told to me about a possible rescue  method by
Mitchell Heller, who's been an engineer involved in recording since  the
early 1950s: humidity. Mitchell said the basic problem is that acetate tape
dries out, and curls as a result. He recommended putting a piece of wet
cloth or  paper towel in at least one corner of a tape enclosure, the more
corners the  better, trying to cover all openings of the enclosure with
something like  plastic wrap to trap the moisture inside, and letting it sit
for a while. He  said that would rehydrate the tape and cause it to flatten
enough to be played  successfully.
  Despite my problems with a few acetate tapes I've never had the  energy to
try it, so I don't know whether it works. Others probably will. In any case,
that's my contribution. I hope to read others' thoughts about the  topic.
  Don Tait