Make a thick, flat slab of clay and pinch a tall ridge along the length of the slab. In cross-section, it should look like a capital letter T. This will not only serve as a handle, but will provide strength as well.
Flip the slab over and impress it with whatever tool or object you like. Since these are quick and easy to make, try several until you get a few you like. Keep in mind that the texture will be reversed when you press the finished stamp into wet clay.
Bisque fire the stamp so that it is rigid but still porous. The fact that it can absorb water will allow it to release from the wet clay surface. Make a lot of these. You never know when you'll need a little bit of texture.
Making the Cup
Peters uses about 1.25 pounds of clay for a cup. If you are going to throw a vessel for stamping, be sure to use a rib to smooth the surface to it will stamp cleanly. This also removes excess water and slip from the surface so the stamp won't absorb too much moisture.
Apply the stamp texture in whatever orientation you like, making sure to press the clay into the stamp's texture. This works better than trying to simply press the texture into the clay without support. Chances are the clay wall will not be able to "push back" against the stamp enough to accept the texture.
Peters uses a propane torch to quickly dry the stamp so it will release more easily from the wet clay.
After the entire surface is stamped, the wall will have been pushed out of round a bit, so going back with a chamois will help smooth and re-center the lip of the vessel.
If you keep the stamp oriented the same way around the vessel, the texture will blend into itself and the "seams" of the texture will tend to visually disappear.
Stay tuned for part two next week when Peters will demonstrate the
trimming of the leather-hard cup, applying a flashing slip to the
outside texture and glazing the inside with a Shino glaze—complete
with recipes and tips for success.