On 2015-Oct-13, at 8:25 AM, Paul Koning wrote: >> On Oct 13, 2015, at 11:19 AM, Jay Jaeger <cu...@charter.net> wrote: >> On 10/13/2015 12:02 AM, tony duell wrote: >>> ... >>> 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. > > 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.
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.) > 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