Sorry to reply so late but I've took a summer hiatus from the ARSC list.  At
this point, my input is surely too late for your likely treatment of the
tapes but I thought you might like some laboratory results collected on
similar contaminants.  Your later e-mail indicated that close examination
showed the contaminant to be chemical in nature rater than mold.  If this is
the case, laboratory testing of similar residues have come up with a variety
of results.  White "powdery" or "crystalline" residues on magnetic tape have
been alternately identified as: cyclic tri-mers from the polyester, sodium
or calcium impurities from the magnetic powder, various fatty acids or
sterates from the lubricant, and surfactants left over from the
manufacturing process.

Whichever the residue may be, wiping the surface of the tape has usually
been sufficient to allow playback.  It should be noted, however, that
playback should be done soon after the residue is removed as, once a tape
has started exuding one of these residues, it may continue to do so and
re-contaminate the surface of the tape.  Care should also be taken in the
cleaning process if extensive crystalline reside is observed as,
occasionally, heavy concentrations of crystals have been observed to bind
adjacent wraps together.

"Baking" tapes with some of these residues has, sometimes, been
counterproductive as the baking process can increase the volume of the
residue on the tape surface.  If you bake the tape to deal with binder
hydrolysis issues, you will want to clean the tape again before playback is

Peter Brothers
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Tape restoration, disaster recovery and re-mastering since 1983

-----Original Message-----
From: Association for Recorded Sound Discussion List
[mailto:[log in to unmask]] On Behalf Of Karl Fitzke
Sent: Tuesday, July 01, 2014 1:26 PM
To: [log in to unmask]
Subject: [ARSCLIST] White Audio Cassette Contaminant

Anyone care to venture any guesses on these photos and what to do about it?
For the time being, I will hold my tongue and not prejudice the jury.  June
1987 recording on 3M/Scotch AVX90 cassette.  There's eight more where this
one came from, recorded from 2nd through 3rd quarter of 1987, and two Scotch
AVM cassettes recorded in early 1988, with similar but significantly less on
edge of tape.


Karl Fitzke
Audio Engineer
Macaulay Library
Cornell Lab of Ornithology
159 Sapsucker Woods Road
Ithaca, NY 14850


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