Using carbon paper is particularly interesting as you cannot tell exactly what you are drawing, and the pen gets stuck in ruts and diverted.
Cutting shapes and peeling, then scanning at different exposures and contrast. The torn edges can be very interesting as well as the sharp cuts.
Try with chocolate: chocolate cats
Different effects are produced on different types of card. It was impossible to really control. But smooth white card glided, absorbent card gave a more water colour effect.
Some intiital C cat sketches
First drawing on canvas, scanned at high contrast.
Next more dilute cats on smooth absorbent cardboard.
Textured effects on corrugated cardboard
Textured effects on corrugated cardboard with thicker chocolate
Large watercolour effect on large card from A4 sketchbook cover. Produced by pouring the left over chocolate in water, then smearing.
Chocolate cat shaper effect with freshly warmed chocalate on shiny white card
Chocolate cats cooler chocolate smudged on shiny white card
Cooler chocolate on light grey cardboard
Drawing over the bits I did not like on the canvas produced new shading effects