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Karl: 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 attempted. Peter Brothers SPECS BROS., LLC 973-777-5055 [log in to unmask] 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. https://cornell.box.com/s/rafx7ue412ylu7svl0j6 -- Karl Fitzke Audio Engineer Macaulay Library Cornell Lab of Ornithology 159 Sapsucker Woods Road Ithaca, NY 14850 607-254-1100 [log in to unmask] Our Mission: To interpret and conserve the Earth's biological diversity through research, education, and citizen science focused on birds.