Have you ever walked through mud puddles and found some of the mud sticking to your toes? That sticky substance is probably clay. You’ll know it is clay for certain if you can shape it with your fingers when it is moist and it keeps the same shape as it dries. Clay comes in lots of different colors depending on what minerals are mixed in with the clay.

Most clay has to be processed to remove impurities and to improve its plasticity. Some potters do this work themselves and others purchase the clay in ready-to-use form. For shaping clay by hand or throwing it on a wheel, the clay should be moist and pliable, but not gushy. To cast it in a mold, it has to be thinned to the consistency of thick cream. Clay in this state is called slip.

Once the clay is shaped, it must be fired in a kiln. This means that the clay piece is heated to a very high temperature – between 1600 and 2200 degrees in a special “oven.” At this extreme temperature, the clay undergoes a chemical change and becomes rigid. It can no longer be dissolved in water. Usually the firing is a slow process, but in raku firing, the process is much faster – and trickier.

After the first (bisque) firing, the clay pieces are often coated with glaze by spraying, dipping or painting. The piece is re-fired, and the glaze melts to the surface of the clay, forming a waterproof seal.

An interesting experiment demonstrates the three different states of clay. You will need an unglazed flowerpot, a glazed coffee mug, and a lump of raw clay. Shape the raw clay into a container. Stop up the hole in the bottom of the flowerpot. Fill all three with water and leave them alone for 24-48 hours. Observe the changes to each container.