Heilbrunn Timeline of Art History Essays

The Technique of Bronze Statuary in Ancient Greece

The ancient Greeks and Romans had a long history of making statuary in bronze. Literally thousands of images of gods and heroes, victorious athletes, statesmen, and philosophers filled temples and sanctuaries, and stood in the public areas of major cities. Over the course of more than a thousand years, Greek and Roman artists created hundreds of statue types whose influence on large-scale statuary from western Europe (and beyond) continues to the present day.

During the third millennium B.C., ancient foundry workers recognized through trial and error that bronze had distinct advantages over pure copper for making statuary. Bronze is an alloy typically composed of 90 percent copper and 10 percent tin, and, because it has a lower melting point than pure copper, it will stay liquid longer when filling a mold. It also produces a better casting than pure copper and has superior tensile strength. While there were many sources for copper around the Mediterranean basin in Greek and Roman antiquity, the island of Cyprus, whose very name derives from the Greek word for copper, was among the most important. Tin, on the other hand, was imported from places as far as southwest Turkey, Afghanistan, and Cornwall, England.

The earliest large-scale Greek bronze statues had very simple forms dictated by their technique of manufacture, known as sphyrelaton (literally, “hammer-driven”), in which parts of the statue are made separately of hammered sheets of metal and attached one to another with rivets. Frequently, these metal sheets were embellished by hammering the bronze over wooden forms in order to produce reliefs, or by incising designs using a technique called tracing.

By the Late Archaic period (ca. 500–480 B.C.), sphyrelaton went out of use as a primary method when lost-wax casting became the major technique for producing bronze statuary. The lost-wax casting of bronze is achieved in three different ways: solid lost-wax casting, hollow lost-wax casting by the direct process, and hollow lost-wax casting by the indirect process. The first method, which is also the earliest and simplest process, calls for a model fashioned in solid wax. This model is surrounded with clay and then heated in order to remove the wax and harden the clay. Next, the mold is inverted and molten metal poured into it. When the metal cools, the bronzesmith breaks open the clay model to reveal a solid bronze reproduction.

Since the physical properties of bronze do not allow large solid casting, the use of solid wax models limited the founder to casting very small figures. To deal with this problem, the ancient Greeks adopted the process of hollow lost-wax casting to make large, freestanding bronze statues. Typically, large-scale sculpture was cast in several pieces, such as the head, torso, arms, and legs. In the direct process of hollow wax casting, the sculptor first builds up a clay core of the approximate size and shape of the intended statue. With large statues, an armature normally made of iron rods is used to help stabilize this core. The clay core is then coated with wax, and vents are added to facilitate the flow of molten metal and allow gases to escape, which ensures a uniform casting. Next the model is completely covered in a coarse outer layer of clay and then heated to remove all the wax, thereby creating a hollow matrix. The mold is reheated for a second, longer, period of time in order to harden the clay and burn out any wax residue. Once this is accomplished, the bronzesmith pours the molten metal into the mold until the entire matrix has been filled. When the bronze has cooled sufficiently, the mold is broken open and the bronze is ready for the finishing process.

In the indirect method of lost-wax casting, the original master model is not lost in the casting process. Therefore, it is possible to recast sections, to make series of the same statue, and to piece-cast large-scale statuary. Because of these advantages, the majority of large-scale ancient Greek and Roman bronze statues were made using the indirect method. First a model for the statue is made in the sculptor’s preferred medium, usually clay. A mold of clay or plaster is then made around the model to replicate its form. This mold is made in as few sections as can be taken off without damaging any undercut modeling. Upon drying, the individual pieces of the mold are removed, reassembled, and secured together. Each mold segment is then lined with a thin layer of beeswax. After this wax has cooled, the mold is removed and the artist checks to see if all the desired details have transferred from the master model; corrections and other details may be rendered in the wax model at this time. The bronzesmith then attaches to the wax model a system of funnels, channels, and vents, and covers the entire structure in one or more layers of clay. As in the direct method, the clay mold is heated and the wax poured out. It is heated again at a higher temperature in order to fire the clay, and then heated one more time when the molten metal is poured in. When this metal cools, the mold is broken open to reveal the cast bronze segment of the statue. Any protrusions left by the pouring channels are cut off, and small imperfections are removed with abrasives. The separately cast parts are then joined together by metallurgical and mechanical means. The skill with which these joins were made in antiquity is one of the greatest technical achievements of Greek and Roman bronzeworking. In the finishing process, decorative details such as hair and other surface design may be emphasized by means of cold-working with a chisel. The ancient Greeks and Romans frequently added eyes inset with glass or stones, teeth and fingernails inlaid with silver, and lips and nipples inlaid with copper, all of which contributed to a bronze statue’s astonishingly lifelike appearance.

Since all but a few ancient bronze statues have been lost or were melted down to reuse the valuable metal, marble copies made during the Roman period provide our primary visual evidence of masterpieces by famous Greek sculptors. Almost all the marble statues in the Mary and Michael Jaharis Gallery at The Metropolitan Museum of Art are Roman copies of bronze statues created by Greek artists some 500 years earlier, during the fifth and fourth centuries B.C.