These were soooooo neat, but it was near the end of school and I didn't get enough photos. So, here's how we did it. I collected styrofoam trays from vegetables I had bought at the store. These are usually a little thicker and work better than the thinner styrofoam dinner plates. Then I made a slideshow (I share these if anyone is interested) to give the students lots of different ideas. They sketched the one or two they chose onto paper.
Next, they sketched them onto the styrofoam (after we had cut off the edges to make sure that it would lay flat), using a ballpoint pen. The indentations are the white spaces that make the design. (See the two examples below.)
The top one is different, though. The trick with this one was that after the student had made his sketch, he indented everything but the sketch, making it stick out from the styrofoam. The result is really neat.
After making a few trial runs, the students made repeated prints with their styrofoam blocks, blotting them on sponges brushed with acrylic paint.

























































