Start with a deep frame.
Place the frame over a wooden board.
Roll out a thin slab using white clay. Be sure to smooth the canvas weave and any wrinkles that the slab roller left behind.
In the hallway lay down a sheet of canvas that you will drop your board onto. If you don't do this the board will crash down and make a loud noise.
Lay your slab over top of your frame. Go into the hallway standing over your canvas sheet.
Make sure the clay is completely covering your frame. You can press the clay into the frame slightly.
Drop your board, frame and clay onto the canvas. The crash will pull your clay evenly into the corners of the frame.
You may want to further push the clay into the corners of your frame. Carefully cut away the remainder of the clay (over hanging the frame).
When your clay is leather hard paint 2 coats of iron oxide slip on the top of your clay and remove the frame. Start carving away some clay into a well thought out design of your choice.