Years ago as a student, lithographic printmaking was my favored media. I loved drawing on stone, and loved how the primarily black and white images looked after printing on fine paper.
As my personal rule for collage-making is to only use source materials that have been created by me or have otherwise come into my own life, I have been harvesting portions of images from some of my former prints. This practice has extended into also using portions of digital prints.
Typically I include colored pencil drawing in the collages to reinforce the visual connections I am making from formerly disparate parts.