First we need to know what sticky shed syndrome is. Most folks who are drawn to this page will already know what it is, but some might be reading this out of simple curiosity, hence the need for explanation. Sticky shed syndrome refers to a phenomenon that occurs in professional quality recording tape made during the 1980's. Tapes made after 1991 are not subject to this problem to nearly the same extent. I ran into it a little later than most when I pulled some tapes out of archive to re-release some music on CD's.
I first tried to playback some two track masters. They were recorded on Ampex 456 tape, ½ inch wide on 10 inch reels. I believe this yields a length of about 2500 feet (I am not sure of the thickness). The thickness is not relevant to the discussion. When I played the tape I found that my machines were playing back with a very jittery tape speed and a terrible wobble in the sound. I couldn't rewind the tapes over the spindles and heads. At first I thought my transports were damaged. Then I noticed that the tapes were sticking to the heads and pinch rollers and tape guides. It was as though my recording tapes had been magically transformed into adhesive tape. In a sense, that is exactly what has happened!
In a fit of frustration I called my old friend, Mitch Hennes. Mitch is an excellent bass player. However, he is also the former head engineer of Streeterville Studios in Chicago. He immediately recognized the problem. He told it was called sticky shed syndrome and the solution to the problem would sound unbelievable. He said I had to cook or bake my tapes - literally! I was to put them into an oven and bake them for hours! He told me that I should do some research to confirm this and get a "repair recipe."
I ended up contacting the Quantegy Corporation. Quantegy made the tape for Ampex and now makes the same tape under its own name. I spoke to Steve Smith for almost two hours. Here is a brief synopsis of his explanation.
Recording tape is made of a polyester backing. On top of that is polyurethane binder (glue) which holds the oxides onto the tape. During the 80's a specific molecular weight was chosen for the binder that the engineers felt would yield the best product. After a few years a problem began to surface, though. Tapes that had been archived in places that had any significant humidity showed this weird stickiness that rendered them unplayable. An explanation was needed.
This was dubbed sticky shed syndrome and is explained in the following manner. The technical name of the culprit is "hydrolysis of the polyurethane." Some sort of chemical reaction occurs when some water molecules get near the polyurethane for some time. The polyurethane molecules then migrate to the surface, thus providing a sticky layer on the surface of the tape. In is not the entire binder layer making its way up there, but only a few molecules thick is apparently enough to make this quite a problem.
The solution? Bake the tapes. The suggested safe approach is to take the tape and set it on a cookie pan in an oven for about 8 hours at 130 degrees Fahrenheit. Now this requires some care. Most cooking oven thermometers are designed for higher temperatures. Also, ovens are control systems driven by a thermostat. They will average 130 degrees, but in the process they will cool below that and heat up to above that as the oven cycles. For you engineering types, a damping factor on the control loop governs how much swing there is, but that's not real important here.
So to repair you tapes, get a candy thermometer and check you oven. Make sure it doesn't go over about 175 degrees Fahrenheit. Above that there will be significant expansion of the tape and this could result in permanent damage. I found that I could get good results a little faster than 8 hours by aiming at about 165 degrees. I would then let my tapes cool down for several hours before I played them. They then were like new.
One engineer in Arizona apparently took his tapes, wrapped them in a blanket and put them on the back seat of his car with the windows closed. He parked in the hot sun and left them there when he went to work. When he came to his car, he got his tapes, let them cool and they were fine. The repairs are not necessarily that scientific.
What is happening in this repair process? Well with the raise in temperature, residual moisture is driven off and the wayward polyurethane molecules migrate right back through oxide back down to the binder layer. My concern was for the information magnetically embedded on the tape - my music! At these temperatures there is no audible effect on the music information embedded on the tapes at all. They will sound like new. Problem solved!
There is one slight problem. In about 30 days, you'll have to do this again. This process will continue like this for the life of the tape. I suppose that if you could find storage in a hermetically sealed environment with extremely low humidity, you might be able to prevent this, but most of us will just bake the tapes whenever we need to replay them in the future.
My tapes were just fine after this treatment. In fact, I did some overdubbing and re-recording with no trouble whatsoever. After I had a solution I found the whole business interesting. At first I was just furious at the thought of losing thousands of man-hours worth of work! What a relief.
For more information contact Steve Smith of the Quantegy corporation at firstname.lastname@example.org.
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