The children have been experimenting with printmaking in first and second grade.  They practiced printing shapes and patterns, as well as images and letters in their sketchbook. We talked  about how some letters have symmetry and some do not. The process is simple but magical and can be repeated(use a damp paper towel to wipe clean the stamp in between colors).  Any vinyl eraser will do(white on one side is okay) and a variety of colors of water based felt tip markers.  Both available for cheap at dollar stores.