13 Oct
2015
13 Oct
'15
11:43 a.m.
On 2015-Oct-13, at 8:25 AM, Paul Koning wrote:
TMK these were generally referred to as electrographic printing.
This sort of scheme goes back to at least the 40/50s for fax machines:
http://www.cs.ubc.ca/~hilpert/e/deskfax/index.html
There the metalisation is on the back of the paper.
Similar technique used in an early 70s calculator, but the metalisation is on the front:
http://www.cs.ubc.ca/~hilpert/eec/calcs/CanonEP151.html
John Wolff describes the mechanism in more detail:
http://www.johnwolff.id.au/calculators/Canon/SE600/SE600.htm
( In these designs there's no wetting involved.)
On Oct 13,
2015, at 11:19 AM, Jay Jaeger <cube1 at charter.net> wrote:
On 10/13/2015 12:02 AM, tony duell wrote:
There are all sorts of oddball printing technologies from back then. I remember one
(from a lab instrument, not a printer or terminal) that used aluminum-coated paper, but
the coating was on the back of the paper. The writing was done with a high voltage
electrode just as you describe, but the result was that the sparks would scorch the paper
and leave a thin black mark. ...
It appears to be electrolytic. You have to keep the paper damp (there is a wick
inside that you put water on. The paper goes between a helical electrode on
a spinning drum and a straight strip, the latter being replaced when you fit a new
roll of paper. Whether it is some chemical in the paper that changes colour, or metal
depositied from the electrode I don't know (the former seems more likely).
I have never got it to work. Whether that is due to electronic problems (that I can
fix) or chemical problems with the old paper (which I can't) I don't yet know.
-tony
I had a little Comprint printer in the 1970s/1980s that used something
sort of like this. The paper was aluminum coated, thus conductive. The
head was a high voltage electrode unit that burned away the aluminum
layer. (I can't imagine any kind of deposition technology in that
era...). The head flew back and forth really fast, doing one pixel-line
at a time. I don't remember what the VT55 used. Tony's
comment does sound plausible; I distinctly remember "electrolytic" printing
technology though no details. I wonder if it might help to take a bit of the paper to a
competent chemist for analysis, to find out what the active ingredient is. That might
help give a clue what is needed to make it work.
paul