Leonardo would give this advice to students in search for inspiration. Wall marks reflect the ongoing passage of human experience. Studying them can yield amazing works of art. Some have called this body of art “Chance Art.” They are a fabrication of accidents from trucks scraping a wall to remnants of graffiti. Still artists from Picasso to Man Ray have used them as a basis of art. I always enjoy finding these special marks in the city, photographing them, and then painting what I see in them.
See "Found Wall Marks" video below