I tried to post this on the [Ampex] list but it may not appear because of creeping HTML content in AOL mail. Others here might be interested in the anecdotal data.
About twelve years ago I salvaged tape from a local studio's radio commercial masters for editing transfers of some oral history material for cassette access. The tape was in Ampex 291, 414, 405; 3M 201, 175, and many white boxes, various lengths.
I found that black oxide back coated tape was useless because of SSS, non-back coated tape was fine, regardless of oxide shade, and brown oxide back coated tape seemed OK. At the time I thought the SSS was a function of the oxide, not the backing so I interspliced the scraps of brown coated and non-back coated tape.
Now I am trying to use these same edited reels to make mp3 files for access. Now the brown oxide back coated tape has serious problems.
Back then, the black oxide back coated tape oxide stuck to the heads and squealed, but did not adhere to the coating. Now some of the brown oxide tape still plays fine, leading me to start rewinding one reel before checking. Before I realized it, about half the oxide of that section had transferred to the backing. Baking that reel recovered the part that had not been damaged, but after baking the oxide on the damaged section fell off in strips!
After that incident, I have been baking all back coated tape, whether it seems to need it or not.
Also the adhesive of the splices on the back coated tape are softened and they come apart during rewind, even on back coated tape that plays OK, while splices on the non-back coated tape in the same reel made at the same time with the same splicing tape are holding just fine.
Baking these composite reels 12 hours at about 60C (dehydrator) recovers the back coated tape without damaging the uncoated tape or the reels (7" plastic, various designs) and even seems to harden the splices in the back coated tape.
This relates to the question of whether it is the oxide binder or the backing that is responsible for sicky-shed syndrome. It seems that the backing alone is enough to cause tape deterioration, though it may take a decade or more longer to have its effect. The completely different behavior of the splicing tape on back coating and plain base may be interesting also.
Obviously mixing types of tape on a single reel is not good practice and nobody on this list would do that, but this provides some idea of the wide variation of tape condition over time even under identical storage conditions (on the same reel).
Mike Csontos