These stains—or " ghosting" —can also appear if you smudge around fresh markings, which shifts around the layers of polymers and pigments, so that the polymers don't form that nice barrier between the pigment and the board.
All those colorful smudges and loose brush work seemed insubstantial and ephemeral when you compared them to the rigorous forms of the cubists and futurists.
When he caught one of his employees eating a pear there, dripping juice onto the grey carpet tiles, he immediately ripped out the stained tile and laid another.