Back when small printers were hard to come by, there
was at
least one technology that used a "paper' made of a black
layer on a paper substrate covered by a very thin layer of
aluminum. The printer burned through the aluminum, leaving
the black spots exposed. Oddly enough, this sounds like a
fiarly permanent process. Was the stuff called
"electrographic" paper?
This might be Readex Microprint technology. I've never seen an example
of Readex output, although the company is a few miles from me and used
to be a microfiche customer. I do know they got significant storage
reduction compared to paper.