Self-hardening clay is available in five pound boxes at hobby stores, dries on its own when left uncovered in about a week, and is paintable. This clay is great for a first-time art project if no kiln is available, and dividing the five pound cube into eight equal sections gives students a large enough piece to make a small coiled pot.
Note: when they say it air-dries, it really does. Open each box in the store and do a push-test with your finger to make sure the clay inside the sealed plastic bag is fairly soft (some boxes we found were much more stiff than others). Use it within a few weeks. Sprinkle leftover clay with water drops and remove as much air as possible before wrapping tightly in its plastic bag, and even then, don’t expect too long of a shelf life after it’s been exposed to air.