Remember that sparking printer, and though never had one myself we had
a machine at work that produced its output the same way - a needle
passed over the paper as it fed through and high voltage pulses blew
the aluminium top layer off to reveal the black paper beneath. Yes it
was slow but this only had to give a single trace ( measured the
surface roughness on grained aluminium plates ).

http://en.wikipedia.org/wiki/Spark_printing

Oh the joys of using that thing