Before beginning to work, the sculptor must decide what material to use. Materials range from something as rare and costly as ivory, which comes from elephants' tusks, to common clay. Good clay is highly prized, but almost anyone can afford it, since it is found in many places all over the world.
The sculptor must decide between a material that is permanent and one that must be made permanent. Each kind has its advantages and disadvantages. A stone like marble is, of course, very hard. Carving must be done with great strength and at the same time with great delicacy. Mistakes are difficult to repair, and too much force can cause breakage. But when a marble statue is carved and polished, the sculptor's work is done. Clay, in contrast, is very soft. The artist can experiment a great deal, adding pieces and remodeling sections. If a mistake is made, the error can be removed quickly. However, clay must be kept workable. Every day the unfinished work must be covered with damp rags, and from time to time the unused clay in the bin must be moistened with water and pounded. Moreover, when the modeling is finished, the statue is by no means ready for exhibition, for clay does not last long. Therefore, the statue must be converted to another kind of material. A number of systems may be used, each requiring additional work. These systems--pointing, firing, and casting--will be described later.
Perhaps because they are permanent, stone and metal have always been important materials for the sculptor. Other materials that have been used include wood, ivory, jade, bone, glass, and plaster. For sculpture that is to be converted to another material, clay is by far the most frequently used substance, but various kinds of wax have also been employed.
In modern times the sculptor has turned to new materials such as one of the plastics, fiberglass, stainless steel, and aluminum.