Analog Tape Sticky Shed Syndrome (SSS)

Discussion in 'TASCAM Analog Forum' started by Mark Richards, Oct 28, 2021.

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  1. Mark Richards

    Mark Richards Well-Known Member

    Dec 2017
    Somewhere Near Nashville
    DP-24, 40-4 MTR, M3 Mixer
    [to be converted to a sticky thread]



    During the heyday of analog recording, Ampex 456 tape was very popular, used by many professional recording studios.

    By the late 1980s, many of those studios discovered that tapes manufactured during the late 1970s into the late 1980s suffered from moisture buildup between the tape layers during storage. This caused the layers to stick together. Similar problems had been reported also on Ampex 406, 407, 457; and similar quality tapes such as manufactured by 3M/Scotch, as well as some tapes manufactured in Japan and Europe.

    Within 7 years of the manufacture date, even if stored in a controlled environment over a number of years, the magnetic coating becomes physically stuck to the back-coating of the tape layer above it.

    The magnetic oxide on the tape layer becomes so sticky from its bonding agent that, when played, it sheds a thick layer of magnetic oxide and gunk in the entire tape path to the point that the take-up reel can't pull the tape onto it and the deck freezes. It takes a diligent effort to clean the gunk off the heads and tape path; and if lucky enough, with even more effort, all the gunk will be cleaned out of the head gap too.

    In response to this problem, experiments by Ampex resulted in a 1989 priority patent - now held by Quantegy - to restore the tape temporarily by baking it. The dry heat of baking removes the moisture and reconditions the tape. Ampex found that baked tape would remain playable for up to four months, after which it will revert to SSS.

    In the 1990s, when my studio started transferring our Ampex 456 masters recorded in the 1980s to digital, every one of them had contracted SSS, failed, and required baking using Ampex's patented process to recover the music.

    Although Ampex also found that an SSS tape could be baked multiple times without further degradation, they recommended that baking only be used to restore the tape so the contents could be transferred to other media.​

    I used Ampex, Scotch and AGFA 2" over the years. They all would soak up humidity from the air and get sticky. Check out this video at 0:29:​

    Brian May talks about baking the 2" for Bohemian Rhapsody and he even showed the sticker "Baked at Harrisons" so they could run it on the 2" one last time and dub to digital.

    In that video, the 2" is Scotch. In the movie, they show a re-creation of the recording session using a 3M M-79 2" multitrack. I have personally done something like 200 sessions on an M-79 and a high number of those sessions were using Scotch tape.

    Baking is kind of an art and yes, the tape goes back to the way it was before it absorbed moisture from the air. Each time you would want to play an old master tape, it would require inspection to determine if it needed re-baking prior to playback.​

    Sony was the only Japanese company to use that binder.

    The idea that the problem is due to back coating is always assumed simply because the bad binder was used only with better tape that had back coating. This does not mean that the back coating was the cause. It must be understood that the binder failure is on the oxide side as the tape would not be stopped at the heads if the back coating was the only fault.​

    Following is a synopsis of the Problem as Stated in the Ampex Patent
    "Some magnetic tapes deteriorate slowly over a number of years, and eventually exhibit the undesirable properties of stickiness and excessive shed of the magnetic oxide coating layer. These properties usually prevent the use of the tapes in equipment for recording or playback. Magnetic tapes currently in use have exhibited these undesirable properties within 7 years of their manufacture."

    " Magnetic recording tape comprises a metal oxide, on a base film that usually also has a back coat on the opposite side of the base film"

    "The [resin binders and other] materials contained in the magnetic coating of current tape are susceptible to exudation over time"

    "The [magnetic coating] binder can exude from the coating causing the tape to be sticky and to shed the magnetic oxide coating from the base film during recording or playback"

    "When the magnetic coating is released from the base film while in use, it collects on the recording and playback heads in the equipment as well as other components along the tape path, and can clog the heads and also impede the transport of the tape"

    While this may be super geek stuff, what really matters is that back-coated Ampex 406/407 and 456/457 (and similar 3M/Scotch tapes) manufactured between the late '70s and late '80s very likely already have the SSS problem or will develop it in due course.

    How to Bake Tape (all sizes and mils - 1/4" through 2")
    The 1989 Ampex patent (linked above) includes instructions for baking the tape.

    Thanks to -mjk-, and SkywaveTDR for their contributions to this sticky thread.
    Last edited: Oct 28, 2021
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