Carving is the oldest known sculpting method, dating back to sculptures made of bone and tusks in prehistoric times. The basic idea of carving is to take a solid block of material such as wood, stone, ice or bone and remove sections to form a desired shape. This is generally achieved by using tools such as chisels, gouges, knives and, in some cases, explosives. Mount Rushmore, for instance, is an example of a massive carving upon which explosives and jackhammers were used.
Modeling is a more hands-on form of sculpture, with the artist often shaping the materials by hand. Using materials such as clay, wax, plaster or other pliable substances, artists form the desired shapes. Large sculptures tend to be built up over solid frames made out of materials such as metal. Smaller pieces can be made from solid pieces of material. The famous faces depicted at Madame Tussaud's waxworks museums are examples of modeled sculptures.
The casting method of sculpture has several steps to achieve the final result. A primary statue is made out of wax or other material that will melt. This statue is carefully packed in clay which is then baked to cause the wax to melt and run out through an opening. This leaves a cavity in the clay in the shape of the desired statue. Molten metal is then poured into the cavity, most commonly bronze is used. The metal hardens and cools then the clay can be broken off, leaving a solid metal version of the first sculpture.
Compared to the other sculpture making techniques, assembling is a new process. It involves the use of various materials assembled together to make a sculpture. These materials can be almost anything, including pipes, bicycles, pieces of plastic or whatever the artist desires. The limits of what can be used and how, are only in the mind of the artists and how they can use the available materials.