I work part-time for a national charity as an art tutor with adult learners and yesterday I took a small group out and about to make graphite rubbings of “street metal” – manholes and stop cock covers. We used Koh-I-Noor graphite blocks (6B) onto Japanese HoSho paper.
When I got back, I photocopied some of the rubbings – the copier changed the colour from black/grey to shades of greyish blue and degraded the quality of the image a bit. I cut up some of these degraded images and played around with them on dark blue card.
scribblah 
I love this idea so much!