i can’t remember where i saw this project.
the way it works is by putting a shape of contact paper (or laminate in our case) on old mat board (or whatever you have), then water color painting over the whole surface. this proved to be a big task and it evolved into an opportunity for teacher-child bonding. we would sit and help them paint their boards when they wanted it.
after the paint isn’t dripping (either because it has dried or because we dab it with paper towel), the kids peel off the laminate.