Portrait bust of a young woman, possibly a sister of Caligula,

second quarter of the 1st century CE

In antiquity, most sculptures were made of bronze, an alloy of copper and tin, using lost-wax casting. A sculptor creates a model, often out of clay, then encases it in another layer of clay, creating a mold. After the mold hardens and is removed from the model, hot wax is poured into it. When the wax hardens, the mold is removed, revealing a wax copy. Clay is then applied to the surface of the wax model and fired. In the process of firing, the wax melts and pours out of holes in the clay. Once the wax has emptied out, bronze is poured inside, creating a thin layer that captures the intricate detail of the original model. The final product is revealed by breaking away the clay mold.