Why can wet clay shrink and crack as it dries?

Wet clay contains tiny solid pieces mixed with water. The water helps the pieces move past one another, so the clay can be pressed into a new shape.

As water leaves the clay and goes into the air, the remaining pieces can draw closer together. The clay becomes smaller. It may also become firmer because the pieces cannot move as easily.

Different parts do not always dry and shrink together. If one part pulls against another, cracks can open. Drying clay and heating a pot in a kiln are different changes, even though both can make clay feel harder.