23 Jan
2022
23 Jan
'22
3:09 p.m.
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,
24 Jan
24 Jan
4:25 p.m.
On Sun, Jan 23, 2022 at 03:09:53PM -0800, Gary Oliver wrote:
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.)
I had done the careful test to find something safe to clean DECtape. One
time I grabbed the wrong bottle and that removed the coating. Tape was now
totally unreadable in that location. Didn't have any luck with cleaning
helping data errors so stopped trying. This was a long time ago so I don't
remember if my incorrect cleaning result matched your description.
7:27 p.m.
On 1/24/22 4:25 PM, David Gesswein via cctech wrote:
On Sun, Jan 23, 2022 at 03:09:53PM -0800, Gary Oliver
wrote:
As to the real reason I was doing this: Most of my tapes are un-boxed
and have suffered being in a dusty area (before I got them) with the
dust forming a sort of 'crust' on the outside of the tape.? It's only on
the first wrap or so, but it's enough that it keeps those handy vinyl
cohesive tapes from sticking.? For that reason, I was trying to find
something to clean of this dusty gunk so the vinyl strip would hold the
tape into a spooled condition. It was the side-effect of this effort
that lead me to the discovery if this "removable layer" on the DECtape.
BTW, does anyone know of a source for these vinyl strips.? My old ones
are 10 mil blue very-flexible vinyl without any adhesive. They rely only
on the cohesive properties of vinyl-to-a-non-porous surface.? I tried
using some of the 'dry vinyl' sheets from Cricut (the plastic decal
printer company.)? They have a couple of colors without adhesive that
they call "window cling" but they aree only 4 mills thick and a bit
flimsy, though so-far they are holding ok.
-Gary
--
-Gary
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.)
I had done the careful test to find something safe to clean DECtape. One
time I grabbed the wrong bottle and that removed the coating. Tape was now
totally unreadable in that location. Didn't have any luck with cleaning
helping data errors so stopped trying. This was a long time ago so I don't
remember if my incorrect cleaning result matched your description. 
25 Jan
25 Jan
6:18 a.m.
On Jan 24, 2022, at 10:27 PM, Gary Oliver via cctech
<cctech at classiccmp.org> wrote:
There's a children's toy I remember: shapes cut from vinyl, intended to be stuck
to windows to make pictures. That seems to be the same stuff.
paul
...
As to the real reason I was doing this: Most of my tapes are un-boxed and have suffered
being in a dusty area (before I got them) with the dust forming a sort of 'crust'
on the outside of the tape. It's only on the first wrap or so, but it's enough
that it keeps those handy vinyl cohesive tapes from sticking. For that reason, I was
trying to find something to clean of this dusty gunk so the vinyl strip would hold the
tape into a spooled condition. It was the side-effect of this effort that lead me to the
discovery if this "removable layer" on the DECtape.
BTW, does anyone know of a source for these vinyl strips. My old ones are 10 mil blue
very-flexible vinyl without any adhesive. They rely only on the cohesive properties of
vinyl-to-a-non-porous surface. I tried using some of the 'dry vinyl' sheets from
Cricut (the plastic decal printer company.) They have a couple of colors without adhesive
that they call "window cling" but they aree only 4 mills thick and a bit flimsy,
though so-far they are holding ok. 
12:13 p.m.
On 1/25/2022 9:18 AM, Paul Koning via cctalk wrote:
Paul,
Are you thinking of Colorforms (https://en.wikipedia.org/wiki/Colorforms)?
To answer Gary's original question: I did find something at
McMaster-Carr: https://www.mcmaster.com/catalog/128/3973 ("Clear
Static-Cling Chemical-Resistant PVC Film").
I don't have any personal experience with it, and it's only 0.007"
thick, so it may not meet Gary's needs.
But if anyone has used it before for tapes I'd love to know if it works
well.
--Bjoren
On Jan 24, 2022, at 10:27 PM, Gary Oliver via
cctech<cctech at classiccmp.org> wrote:
There's a children's toy I remember:
shapes cut from vinyl, intended to be stuck to windows to make pictures. That seems to be
the same stuff.
paul
...
As to the real reason I was doing
this: Most of my tapes are un-boxed and have suffered being in a dusty area (before I got
them) with the dust forming a sort of 'crust' on the outside of the tape.
It's only on the first wrap or so, but it's enough that it keeps those handy vinyl
cohesive tapes from sticking. For that reason, I was trying to find something to clean of
this dusty gunk so the vinyl strip would hold the tape into a spooled condition. It was
the side-effect of this effort that lead me to the discovery if this "removable
layer" on the DECtape.
BTW, does anyone know of a source for these vinyl strips. My old ones are 10 mil blue
very-flexible vinyl without any adhesive. They rely only on the cohesive properties of
vinyl-to-a-non-porous surface. I tried using some of the 'dry vinyl' sheets from
Cricut (the plastic decal printer company.) They have a couple of colors without adhesive
that they call "window cling" but they aree only 4 mills thick and a bit flimsy,
though so-far they are holding ok.
12:24 p.m.
On Jan 25, 2022, at 3:13 PM, Bjoren Davis via cctalk
<cctalk at classiccmp.org> wrote:
On 1/25/2022 9:18 AM, Paul Koning via cctalk wrote:
Paul,
Are you thinking of Colorforms (https://en.wikipedia.org/wiki/Colorforms)?
Yes, that's it. I would think those will work fine. I remember having something
similar as a kid and what I remember is that the thickness was similar to that of DECtape
"little blue things".
paul
On Jan 24, 2022, at 10:27 PM, Gary Oliver via
cctech<cctech at classiccmp.org> wrote:
There's a children's toy I remember:
shapes cut from vinyl, intended to be stuck to windows to make pictures. That seems to be
the same stuff.
paul
...
BTW, does anyone know of a source for these vinyl strips. My old ones are 10 mil blue
very-flexible vinyl without any adhesive. They rely only on the cohesive properties of
vinyl-to-a-non-porous surface. I tried using some of the 'dry vinyl' sheets from
Cricut (the plastic decal printer company.) They have a couple of colors without adhesive
that they call "window cling" but they aree only 4 mills thick and a bit flimsy,
though so-far they are holding ok. 
12:24 p.m.
On 1/25/22 06:18, Paul Koning via cctalk wrote:
The term of art is "cling vinyl" or "static cling vinyl". Most art
stores carry the stuff--mine is a package of this:
https://www.grafixplastics.com/materials-plastic-film-plastic-sheets/commod…
Cut the strips with a paper cutter and you'll have enough in a package
to last you well into your sunset days.
--Chuck
On Jan 24, 2022, at 10:27 PM, Gary Oliver via
cctech <cctech at classiccmp.org> wrote:
There's a children's toy I remember: shapes cut from vinyl, intended to be stuck
to windows to make pictures. That seems to be the same stuff.
...
As to the real reason I was doing this: Most of my tapes are un-boxed and have suffered
being in a dusty area (before I got them) with the dust forming a sort of 'crust'
on the outside of the tape. It's only on the first wrap or so, but it's enough
that it keeps those handy vinyl cohesive tapes from sticking. For that reason, I was
trying to find something to clean of this dusty gunk so the vinyl strip would hold the
tape into a spooled condition. It was the side-effect of this effort that lead me to the
discovery if this "removable layer" on the DECtape.
BTW, does anyone know of a source for these vinyl strips. My old ones are 10 mil blue
very-flexible vinyl without any adhesive. They rely only on the cohesive properties of
vinyl-to-a-non-porous surface. I tried using some of the 'dry vinyl' sheets from
Cricut (the plastic decal printer company.) They have a couple of colors without adhesive
that they call "window cling" but they aree only 4 mills thick and a bit flimsy,
though so-far they are holding ok.
2:06 p.m.
On 1/25/22 12:24 PM, Chuck Guzis via cctalk wrote:
On 1/25/22 06:18, Paul Koning via cctalk wrote:
The term of art is "cling vinyl" or "static cling vinyl".
Most art
stores carry the stuff--mine is a package of this:
https://www.grafixplastics.com/materials-plastic-film-plastic-sheets/commod…
Cut the strips with a paper cutter and you'll have enough in a package
to last you well into your sunset days.
--Chuck
My search results were dominated (even with 'advanced search') by Amazon
and Ebay (naturally) but also by a couple of vendors (Cricut as example)
and I never found anything coming up for .10 inch or equivalent in mm.?
This appears to be .10 inches without adhesive so I'm going to give this
a try.
Thanks VERY MUCH for this link.
--
-Gary
On Jan 24, 2022, at 10:27 PM, Gary Oliver via
cctech <cctech at classiccmp.org> wrote:
There's a children's toy I remember:
shapes cut from vinyl, intended to be stuck to windows to make pictures. That seems to be
the same stuff.
...
As to the real reason I was doing
this: Most of my tapes are un-boxed and have suffered being in a dusty area (before I got
them) with the dust forming a sort of 'crust' on the outside of the tape.
It's only on the first wrap or so, but it's enough that it keeps those handy vinyl
cohesive tapes from sticking. For that reason, I was trying to find something to clean of
this dusty gunk so the vinyl strip would hold the tape into a spooled condition. It was
the side-effect of this effort that lead me to the discovery if this "removable
layer" on the DECtape.
BTW, does anyone know of a source for these vinyl strips. My old ones are 10 mil blue
very-flexible vinyl without any adhesive. They rely only on the cohesive properties of
vinyl-to-a-non-porous surface. I tried using some of the 'dry vinyl' sheets from
Cricut (the plastic decal printer company.) They have a couple of colors without adhesive
that they call "window cling" but they aree only 4 mills thick and a bit flimsy,
though so-far they are holding ok.
2:37 p.m.
On 1/25/22 14:06, Gary Oliver via cctalk wrote:
My search results were dominated (even with
'advanced search') by Amazon
and Ebay (naturally) but also by a couple of vendors (Cricut as example)
and I never found anything coming up for .10 inch or equivalent in mm.?
This appears to be .10 inches without adhesive so I'm going to give this
a try.
Thanks VERY MUCH for this link.
I found another use for the stuff that may be worth mentioning. I
repaired a damaged cable jacket--just wrap a strip of the stuff around
the damaged area and apply heat sufficient to fuse the stuff to itself.
No adhesives involved.
--Chuck
26 Jan
26 Jan
10:28 a.m.
On Jan 24, 2022, at 10:27 PM, Gary Oliver via cctech
<cctech at classiccmp.org> wrote:
...
As to the real reason I was doing this: Most of my tapes are un-boxed and
1:59 p.m.
On Jan 26, 2022, at 1:28 PM, Tom Gardner via cctalk
<cctalk at classiccmp.org> wrote:
...The UNISERVO I, of Univac I, tape drives had a separate spool of clear
very thin film that was clock motor wound across the head when tape was
moving, since the phosphor bronze plated tape was very abrasive. That
existed long before LINCtape/DECtape."
Note that LINCtape is DECtape :-)
Media-wise, yes. The format is very different indeed.
paul
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