How Is a Bronze Statue Made? Destroying the Original to Get the Copy

The full process, in the indirect form used for any work of size, runs through a long chain of stages:

• •The artist makes an original in clay, plaster or another workable material, which is not the thing that will be melted
• •A flexible mould is taken from that original, historically in plaster and now usually in silicone rubber backed by a rigid case
• •Molten wax is poured into the mould and swilled around, building a hollow wax shell of even thickness that is then removed and refined by hand, since this wax is what the bronze will copy exactly
• •A core of refractory material fills the interior, held by metal pins so it cannot shift, which is what makes the casting hollow and saves enormous weight and metal
• •Wax rods are attached to form channels, called sprues and risers, through which metal will enter and air and gas will escape
• •The whole assembly is invested, dipped repeatedly in ceramic slurry and sand until a thick shell builds up, or packed into a mould of plaster and sand
• •The mould is fired, which hardens the shell and melts the wax out, leaving a cavity of exactly the sculpture's shape
• •Bronze at around eleven hundred degrees is poured in, the mould is broken away, the sprues are cut off and the surface is chased, meaning worked over to remove seams and restore detail

Bronze is copper alloyed with tin, commonly with small additions of zinc and lead in modern statuary alloys, and its properties suit casting unusually well. It melts at a temperature achievable with pre-industrial furnaces, flows into fine detail while molten, and expands very slightly as it solidifies, which presses it into the mould and captures surface texture down to fingerprints in the wax. It is strong in tension, unlike marble or stone, which means a bronze figure can have an outstretched arm or stand on one leg, poses that would snap in stone and are the reason classical marble copies of bronze originals carry awkward tree stumps and struts as supports. It resists corrosion by forming a stable surface patina, which can be encouraged deliberately with chemicals and heat to produce colours from near black through browns to greens and blues, a finishing stage that is a craft in its own right and substantially determines how the finished work reads.

A figure larger than a certain size cannot be poured in one piece, because the metal would cool before filling the mould and the stresses would crack it. Large works are therefore cast in sections, which are welded together and the joins chased until invisible, a practice used since antiquity and clearly visible in ancient pieces where the joins have opened. The other consequence of the method is that because the wax comes from a reusable mould rather than from the artist's hand, a work can be cast repeatedly, which raises the question of what an original is. The convention that developed treats a limited edition as legitimate, with each cast numbered and the moulds destroyed afterwards, and legal limits exist in several countries, with French law restricting an edition of a sculpture to twelve casts if they are to count as original works. Posthumous casts made from an artist's moulds after death are a persistent grey area and a persistent source of dispute.

Very little ancient bronze sculpture survives, and the reason is that bronze is valuable and remeltable. Statues were melted for coinage, weapons and cannon throughout history, so that the great bronzes of classical Greece are known almost entirely through Roman marble copies, and the handful of survivors are mostly pieces that were lost at sea and recovered much later, including the Riace warriors found off Calabria in 1972 and the Artemision bronze. The same logic applies to more recent history, with wartime requisition melting down statues and even railings across Europe. Bronze that survives outdoors faces a different problem: acidic pollution converts the stable patina into soluble compounds that wash away, progressively etching the surface, which is why conservation of outdoor bronzes involves cleaning, stabilising and applying protective wax coatings on a regular cycle rather than being a one-off treatment.

Lost wax casting builds a wax copy from a mould of the artist's original, encases it in a refractory shell, melts the wax out and pours bronze into the void, then breaks the shell away. A core makes the casting hollow, sprues carry the metal in and gases out, and the surface is chased and patinated afterwards. Bronze suits the method because it flows into detail, expands slightly on setting and is strong in tension, allowing poses that would break in stone. Almost no ancient bronze survives because it was remelted.