Dirtying the paper delicately.
“All art is but dirtying the paper delicately.”
― John Ruskin
In the comments section of my post Broken and bare branches yesterday 
Because of the nature of this charcoal material the drawing was very faint and the roughness of the charred wood determined the style of the lines, so I had to learn the idiosyncrasies of the medium and work with it. In a way I was ''dirtying the paper delicately.”