Although modern sculptors employ a wide range of methods and an expansive variety of artistic techniques in the creation of a piece, classical sculpture was limited for the most part to two basic types, carving and casting. Carving begins with a large piece of material such as stone, ivory, or wood. The artist, using a hammer and chisel, a knife, or even sandpaper, then begins the process of reducing it1 down to the shape or form desired. Thus, carving is essentially a process of removal and, as such, is limited by the size and physical properties inherent in the material to be carved. Further, because large blocks of marble, for example, are extremely expensive, it is imperative that the sculptor both understand the characteristics of the medium and work first with scale models of the piece to be produced. One of the most famous sculptures produced by carving is Michelangelo's David, an invaluable piece, created over a three-year period of time, that seems to bring life to the marble in which it2 was carved. Casting involves a completely different process. In casting , the artist first produces a model of the piece to be created out of clay or some other easy-to-manipulate substance. Plaster--a liquid made of lime, sand, and water that hardens over time-- is then used to make a mold around the model. The mold conforms to the shape of the clay model, hardens, and is then opened (or carefully split into two pieces) for the removal of the clay model. The mold is now ready to be used for casting. In the casting step, the mold is reassembled, and plaster, bronze, or some other material is poured inside through a small hole. Once the material inside hardens, the mold is shattered or chipped away, leaving a cast of the original clay model, which can then be painted or adorned as the artist pleases. The Burgher of Calais, a bronze statue by Rodin commemorating an important event in French history, is a fine example of the work that can be created using this method.