Question about DECtape formulation
Gary Oliver
go at aerodesic.com
Sun Jan 23 17:09:53 CST 2022
I've always thought the physical tape wound on a DECtape spool was a
fairly conventional 'sandwich' of mylar/oxide/mylar, but a recent 'test'
makes me think there is something else involved.
I have a number of tapes I'm cleaning (removing dust, etc.) to make
ready to read on a restored (apparently) Astrotype dual DECtape drive
and I was 'dressing' the leaders of the tape (removing ragged bits from
old use.) After trimming a wee bit from several tapes (.5 to 1 inch) I
did a test. Taking the bits of tape, I exposed them to various
concentrations of isopropanol/water (from about 25% to 99% iso) and
found than in all cases, some of the data side of the tape came off on
the wipe. The remaining tape fragment appears intact - the brown oxide
was still there but both sides were now the same color, rather than the
data side being darker (as were all my tapes before the test.)
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, other than the "...hydro- dynamic lubrication, relying on
the viscosity of air to entrain it with the tape and provide the
flotation medium." found in an "ELECTROMECHANICAL COMPONENTS & SYSTEMS
DESIGN" from November, 1964.
All of my tapes, including DECtape brand, Scotch brand and even a couple
of old "Microtape" brand from DEC (before 'dectape' name change) have
this feature, so this doesn't appear to be something that appeared
recently (as in late in DECtape production or due to old-age in the tapes.)
If someone has some detail information on the tape construction, I'd am
curious to see it.
Thanks,
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