Set a slab of clay on a flat surface and unwrap it. Test the clay by pushing on it to ensure it's moist enough to knead. Sprinkle some water onto the surface of the clay and knead it in, if the clay is too stiff to knead.
Sprinkle a small handful of unpopped popcorn, perlite or vermiculite onto the surface of the clay.
Knead the clay by pushing on it and folding it over to mix in the added particles. Scoop up any fallen particles and add them to the clay as you continue to knead it.
Sprinkle more particles into the clay and knead it again until the clay has the desired texture.
Put the clay pot on a potter's wheel. Start the wheel and shape the pot. Stop the wheel and remove the pot. Let the clay pot dry, then fire it in a kiln. You can add a glaze prior to firing the clay pot.
Cut patterns into one side of two or three old credit cards. For example, cut a triangle pattern into one card, a curving line along the side of another card and a scalloped edge on a third card. Pull off any debris on the cut edges.
Put the cards next to your potter's wheel. Add clay to the potter's wheel and start the wheel. Continue feeding clay onto the spinning pot until you have the shape you desire.
Keep the wheel going and hold the pot with one hand. Hold a cut credit card against the side of the pot with your other hand to create a ribbed texture on the pot.
Put down the first credit card. Hold another cut credit card against the rim of the pot to create a different ribbed texture at the top of the clay pot.
Stop the potter's wheel and examine the ribbed effect. If you're not satisfied with the texture, score the clay pot while it's stationary by dragging a cut credit card around the outside of the clay pot for a lighter texture.