USE ANYTHING YOU CAN FIND, NOT JUST INK
The Xerox was an instamatic camera which came out with a solid black & white image of whatever you placed under its eye.
Like the pioneers of early camera techniques, especially of those of Man Ray with his “rayograms” in the 30’s, he placed many objects onto the glass platen, arranging them into compositions that would ultimately remain untouched after they were “Xeroxed” – the paper proofs