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On 1/24/16 1:33 PM, John Haley wrote:
> I have followed this long thread but frankly have found a lot of it
> confusing.  David, I have always assumed it is in fact the black
> back-coating that is what has turned sticky and gums up the machine on
> unbaked tapes.  It wouldn't be the oxide layer coming off like that.

In my experience, which is mostly with Ampex tape, both the oxide and 
the backcoating are sticky, and some of the oxide is coming off when an 
unbaked tape is played.  The deposit that forms on heads and guides 
exposed to the oxide side of the tape is mostly oxide, although 
initially it seems to be somewhat darker in color than the oxide.  I 
think some of the backcoating becomes embedded in the oxide.

In the worst case, large chunks of oxide are so solidly attached to the 
backcoating that they are pulled off the base.  (But I've never seen 
large chunks of backcoating pulled off the base.....)

The deposit that forms on static surfaces exposed to the back of the 
tape is mostly backcoating.

-- John Chester