On 1/24/22 7:30 AM, Paul Koning via cctalk wrote:
On Jan 23, 2022, at 8:40 PM, Noel Chiappa via cctalk<cctalk@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
I also have tried the alcohol wiping on a piece from a 'fresh' tape
(never used - still with tape seal) and the results were the same.
The procedure was to slightly dampen a piece of lint-less paper towel
(e.g. kimwipe) with the alcohol solution and wipe with minimal force
over a small portion of the 'data' side of the tape. (I used 25%, 50%
and full strength alcohol and all were identical except for time
required to remove the layer.) Removing the dark brown/grey 'coating',
allows the brown oxide to show. After this step, the top and bottom of
the tape looked identical (a medium color iron oxide.) This 'exposed'
oxide did not seem to be any easier to scrap off using a sharp exacto
knife (no oxide residue when scraping, but clearly left scrape marks on
the tape) suggesting there is still a robust protecting layer left on
the tape.
Also, after removal of the layer with alcohol, there was no apparent
thickness change. I haven't used a micrometer yet to verify, but the
'fingernail' test doesn't indicate any thickness layer boundary between
the 'cleaned' and 'uncleaned' portions.
Paul - thanks for the bitsavers reference. I thought I had copied all
of the DEC documents relating to DECtape, but clearly missed that one.
--
-Gary
