I'm doing a lesson using pieces of wall board. I bought a 5x8 sheet at home depot for 5.67. I cut it up into 8x10in pieces. I had students glue a cardboard backing on each. When the glue dries, use sponge and water to remove the paper off one side, carefully. If the board cracks, the cardboard holds it together and you can glue it. They are carving designs in relief and painting with watercolor. They have a "rock like" quality and I can picture them looking like "cave art"
I'm at high school level and so far the kids are very intense with their carvings.