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ACS Examines Tape Degradation

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  • ACS Examines Tape Degradation

    Unwinding the mystery of degraded reel-to-reel tapes

    A brown “sticky shed” residue on an unplayable reel-to-reel tape is shown accumulating at a playback machine’s contact points; the residue disappears upon heating.

    Credit: Andrew R. Davis
    Click here to download the image.
    WASHINGTON, April 8, 2020 — Crooner Bing Crosby knew a thing or two about sound. In 1947, recognizing that recorded music sounded better on magnetic reel-to-reel tape than on vinyl records, he invested in a company to develop equipment to record his radio shows. Soon, reel-to-reel tapes and recording and playback machines were a household craze. Now, as reel-to-reel tapes make a comeback among audio buffs, scientists are unraveling the secret of why some decades-old tapes are unplayable, while others retain their original superb audio fidelity.

    The researchers are presenting their results through the American Chemical Society (ACS) SciMeetings online platform.

    “It is a mystery why some tapes hold up and others don’t,” says Andrew R. Davis, Ph.D. “I talked to audio technicians to ask what they do to remedy unplayable tapes. They knew that heating degraded tapes worked, and they used everything from toaster ovens to hair dryers. But no one knew exactly why heat worked, and sometimes the tapes reverted quickly to being unplayable. We are trying to find out why.”

    The project is of special interest to Davis, a polymer chemist at the Library of Congress (LC), which has nearly 200,000 reels of audio tapes spanning recordings of popular musicians, National Public Radio (NPR) broadcast archives and the American Folklife Center. The collections are used by scholars and documentary producers around the world. Universities, private citizens and museums also have aging reel-to-reel tapes, and Davis emphasizes that his work could help them preserve recordings in their collections, as well.

    Reel-to-reel tapes are generally comprised of a multilayer polyester-urethane polymer containing various additives and lubricants. Tapes that degrade often have “sticky-shed syndrome,” which is created by the deterioration of binders in a magnetic tape that hold the iron oxide magnetizable coating to its plastic carrier or that hold the thinner back-coating on the outside of the tape. Sticky-shed syndrome leaves a residue that can damage the tape and playback equipment.

    The sweet spot for thermal treatment of tapes appears to be around 130 F, Davis says. In his studies, Davis used sample tapes from LC’s analytical lab that are representative of the library’s valuable collections. On most of the tapes he studied, he observed that residues on the surface of the binder layer were crystalline and polyester-like. He also found that these residues melted back into the bulk polymer layer upon heating, turning an unplayable tape into a playable one. It turns out that the crystals re-appear, or bloom, on the tape surface when they become unplayable again. His studies of thermal transitions in the magnetic layer and polyethylene terephthalate support film indicate that a single component does not account for tape degradation and that the detrimental residues are not isolated to the tape binder layer.

    “This research also confirmed what we heard from audio technicians, that thermally treated tapes that were wound on reels reverted to a visibly deteriorated condition within a few weeks,” Davis says. “Surprisingly, we found that when our small unwound test samples of tape were thermally treated, they appeared to be optically fine even after weeks. Clearly being wound has some effect on the tapes.”

    “One explanation is that when you bake and melt the tape residues, they transfer to the backside of the adjacent, nonmagnetic layer of tape. As it cools down, it retransfers to the oxide layer if the tape is tightly wound,” Davis says. “Or perhaps the pressure of winding the reel has something to do with the melting and recrystallization process.” Davis and his colleagues are studying those possibilities now.

    Despite the ongoing mystery, Davis has advice for people who love their stashes of reel-to-reel tapes and want to know how to store or restore their old tapes. “The best bet is to buy a good technical oven to control the temperature of restoration and good playback equipment, rather than highly specific environmental controls,” he says. “You probably wouldn’t want to store your tapes in a sauna, but normal seasonal changes in temperature and humidity seem to bode well for tape storage.”

    The researchers acknowledge support and funding from the Library of Congress.

    The American Chemical Society (ACS) is a nonprofit organization chartered by the U.S. Congress. ACS’ mission is to advance the broader chemistry enterprise and its practitioners for the benefit of Earth and its people. The Society is a global leader in providing access to chemistry-related information and research through its multiple research solutions, peer-reviewed journals, scientific conferences, eBooks and weekly news periodical Chemical & Engineering News. ACS journals are among the most cited, most trusted and most read within the scientific literature; however, ACS itself does not conduct chemical research. As a specialist in scientific information solutions (including SciFinder® and STN®), its CAS division powers global research, discovery and innovation. ACS’ main offices are in Washington, D.C., and Columbus, Ohio.

    To automatically receive press releases from the American Chemical Society, contact [email protected].
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  • #2
    Very interesting. Those of us who have experience with sticky shed (mine is mostly with Ampex 456) have invested (given the price of tape, probably not the right word) in a food dehyrator, know that the sweet spot most of us use the 125 degree setting. So having the ACS confirm that the sweet spot is 130 is nice to read. And a $60 to $80 food dehydrator is a lot cheaper than a technical oven. Larry
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    • #3
      And having baked dozens of tapes in a food dehydrator with perfect results, I can confirm it’s all that’s required.
      TAPE: Studer A807, A810; Revox B77 MkII; Tascam BR-20; Technics RS-1700; Pioneer RT-707, RT-909
      VINYL: Denon DP59-L/Benz LP-S MR/ModWright PH 9.0; Pioneer PL-50LII/Dynavector 20xH
      DIGITAL: Bryston SP-3, Marantz NA6006/Pioneer N-50, Schiit Bifrost
      SPEAKERS: B&W Nautilus 800, Pioneer DSS-9, Velodyne FSR-15
      AMPS: Cary SLP-05/Sunfire Signature 600, Pioneer SX-1980


      • #4
        I have baked quite a few from 1/4" to 1" tapes. I use the 130 degree setting on my dehydrator as well. For the 1/4" I put them in the dehydrator when I leave the office and bake them over night, then let them cool for a day before playing. For the 1/2" I let them go until at least noon before removing them and for the 1" I let them go for 24 hours, then cool over night before playing them. Over time they well revert back to SSS. So it is best to transfer them with in 24 hours of the baking process. Just keep in mind they need to come to room temperature before putting them on a machine for transferring. Most of the problem tapes have been 456 and some 3M 226.


        • El Magnifico
          El Magnifico commented
          Editing a comment
          Yep, the 456 has been a bitch for a long time here as well. Your formula is what we use too. It works!

      • #5
        I've been using 130 degrees for years now. As Don mentioned, it's a good temperature for all tapes. It works perfectly EVERY time and you can actually re-dehydrate tapes over and over again without damaging them. It's always handy to have a food thermometer to check the temperatures as well. The digital ones made by Taylor are excellent for this purpose. The biggest advantage that I see about using the dehydrator is the fan. Not only are you adding the required amount of heat but you are also blowing the moisture out with the rising hot air.

        Among other SSS tapes, there is Ampex 406/407 which is perhaps the worst of all the problem tapes because tapes that are even WOUND before baking can suffer from catastrophic shedding after baking where the oxide comes off the backing in sheets. DON'T EVER play or wind a roll of known 406/7 without baking first. Another culprit is Scotch 250 although it appears to be the least troublesome of all the types. I have had rolls of Scotch 996 & 986 that have also had the sticky shed problem.


        • #6
          I will add to the list, 3M 226 and Agfa 469, (not 468). and Ampex 457.


          • #7
            The best I've found for baking tapes is this below. But pretty big so check dimensions. But flawless and so convenient. Shuts off automatically when done. Holds at least 8 tapes of 1/4" size.


            • #8
              Has someone found life myself, that even with baking Ampex 456 still sheds? My 456 sheds still even when baked -- but is useable to copy.


              • Don RMGI
                Don RMGI commented
                Editing a comment
                I have only had that happen on one tape so far. It wasn't terrible, so like you I just made the transfer and moved on.

            • #9
              Originally posted by jonathanhorwich View Post
              Has someone found life myself, that even with baking Ampex 456 still sheds? My 456 sheds still even when baked -- but is useable to copy.
              I haven’t actually seen this with 456, but I have once with 406. Wasn’t sticky after baking but still shed an alarming amount, just a dry shed. But this tape clearly hadn’t been stored even close to properly.
              TAPE: Studer A807, A810; Revox B77 MkII; Tascam BR-20; Technics RS-1700; Pioneer RT-707, RT-909
              VINYL: Denon DP59-L/Benz LP-S MR/ModWright PH 9.0; Pioneer PL-50LII/Dynavector 20xH
              DIGITAL: Bryston SP-3, Marantz NA6006/Pioneer N-50, Schiit Bifrost
              SPEAKERS: B&W Nautilus 800, Pioneer DSS-9, Velodyne FSR-15
              AMPS: Cary SLP-05/Sunfire Signature 600, Pioneer SX-1980


              • jonathanhorwich
                jonathanhorwich commented
                Editing a comment
                Yes, exactly. Dry shedding. Maybe I was baking too conservatively at 120 F for 24 hours. 130F might eliminate some of this dry shedding.