Using trash to paint on is kind of a fun idea for found object art, especially when it is nice and funky street art. Rik Catlow (top pic) has a bit of a how to for the smashed can paintings here. And I love the pink art on smashed spray paint cans by Buff Monster (bottom pic).
Also a fun idea for kids, it lets them think out of the box in regards to raw materials for their art. A kids page here.
