Modeling Clays have several distinct properties that make them useful. Unlike firing clays used in pottery, oil-based clays stay soft and workable. They never harden or dry, but that means they also cannot be fired. They can be pigmented too, with a wide array of bright colors that can be blended still further. Although some professional products are pigmented, scholastic modeling clays are the most brightly colored. They are also the softest and easiest to work with, although they won't hold detail as well.
Although the name is not used as often in the United States, plastilina is a generic term for oil-based modeling clay. Plastilina was developed in Germany in the 1880s. Plastilina was originally a trade name, like aspirin and nylon, but the name lost its trademark status when it came into general use. Today, many professional modeling clay products still go by this name, plastilina.