Scotch 3M 399 color videotape (their first "color" model introduced at the beginning of the high-band color era in 1965 +/-) is non-backcoated but it has shown stickiness and black oxide shed until baked. However, that polyester base and it's coating, although a S/N improvement over 379, is very precarious to use due to pack slippage and oxide just falling off of the base with even the best practices of handling. I have found countless instances of cinching when the tape container is first opened up. The same situation applies to some non-backcoated 1" type A tape I've recovered.
On Jan 24, 2016, at 12:41 PM, John Schroth wrote:
> Back-coating may instigate or speed up the hydrolysis process but I cannot ignore the fact that there are still obscure instances where the tape had no back-coating and suffered from SS. Richard, you have noted this in the past and I have had this happen in at least two instances that I can recall. I'm at home today so I don't have access to my notes, but it was clearly sticky shed on tapes that had no back-coating. So one should not "always" equate back-coating with sticky shed.
> Just my two cents...
> John Schroth
> On 1/24/2016 2:05 PM, John Chester wrote:
>> 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
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