Bronze casting using the "lost wax" method

http://www.cantorfoundation.org/Rodin/Bronze/casting1.html

1. The sculptor creates a model, which is generally made of plaster, clay, marble, stone, or wood.
2. An impression of the model is made in a bed of very fine, elastic material supported by a rigid outer mold. The supportive layer is designed to withstand the pressure of melted wax running through the mold.
3. This sharply defined mold is used to create a fireproof clay model, identical to the artist's original model.
4. The surface of the clay model is scraped, reducing it by the desired thickness of the final bronze.
5. After closing the mold around the clay model, wax is poured into the space between the model and the mold. This stage is crucial in producing a perfect reproduction of the initial sculpture. The result is a wax model which is hand finished to fidelity, incorporating the artist's signature, cast number and foundry seal.
6. A network of wax conduits, called sprues and gates, are attached to the model. They act as channels through which the wax, when heated, will escape.
7. A finely granulated ceramic is gradually applied to the surface of the model and its conduits until it becomes thick and coarse. The end result is called an investment mold. The mold is then dried and heated; melted wax now flows through the mold, leaving a space between the fire resistant clay model and the investment mold. This method of losing the wax is called the "lost wax method."
8. The investment mold is then heated to a high temperature and covered with a coating, which must be completely dry before bronze pouring begins.
9. Molten bronze is then poured into the cavity of the mold, filling the space left by the wax model. The mold is broken and the metal appears - the figure and its conduits are an exact reproduction of the wax figure in Step 6.
10. The network of conduits are then cut and worked so that no trace of them can be seen. This procedure of hand finishing the bronze to perfection is called "chasing." Remains of the fireproof clay model left inside the bronze are now removed.
11. Upon completion of the chasing, hot or cold oxides are applied to the surface of the bronze creating a thin layer of corrosion. This layer, usually brown, green or blue in color, is called the patina.