Flatten the clay slightly, either by pounding it with your hands or by throwing it at an angle onto a flat surface.
Pull the roller bar all the way to one side by rolling the wheel.
Place the canvas on the slab roller table.
Place the clay on the canvas, more than half the length of the table away from the roller bar.
Fold the canvas over the clay, with the fold several inches away from the clay.
Roll the wheel the opposite direction from before to pull the roller bar over the clay.
Roll the roller bar back over the clay.
Remove the top layer of canvas and take the clay slab off the table.