Question about DECtape formulation

[Paul Koning]

> On Jan 23, 2022, at 8:40 PM, Noel Chiappa via cctalk <cctalk at classiccmp.org> wrote:
> 
>> From: Gary Oliver
> 
>> I've always thought the physical tape wound on a DECtape spool was a
>> fairly conventional 'sandwich' of mylar/oxide/mylar ...
>> Was there some kind of 'lubricating' coat on the data side? It makes
>> sense, but none of my DEC documents or Googling has any mention of
>> lubrication ...
>> If someone has some detail information on the tape construction, I'd am
>> curious to see it.
> 
> Dunno if you know of this:
> 
>  http://www.bitsavers.org/pdf/dec/dectape/3M_DECtape_Spec_Nov66.pdf
> 
> but it doesn't mention any lubrication, just a "Protective Overlay" layer,
> over the "Coating" (which I assume is the oxide). I'm a bit surprised that
> "some of the data side of the tape came off on the wipe", though, unless the
> "various concentrations of isopropanol/water" dissolved the Protective
> Overlay.
> 
> 	Noel

Depending on how much the tape has been used, it's possible that the top layer has worn through.  I have known that to happen on highly used tapes, though not many got enough to wear that far.

It also might be oxide tranferred from one tape to the head to other tapes, if the heads weren't cleaned enough.

	paul