The History of Bronze Casting
History of the Lost Wax method
There is no accurate record of when the lost wax method of bronze casting was first utilized.
It is believed the earliest users of the lost wax method began with a clay core roughly the shape of the subject to be sculpted. This core was covered with wax and then sculpted to the finished form. Once the wax hardened it was covered with clay. The object was baked, hardening the clay and melting the wax. Because the wax method melted out the bottom of the baking receptacle or oven, it was unusable or lost – hence the process is called “Lost Wax”. The space evacuated by the wax was then filled with molten bronze. Once the bronze cooled and hardened, the clay was removed, and the remaining bronze was cleaned and polished.
Other names for the process include “lost mold,” which recognizes that other materials besides wax can be used, including but not limited to tallow, resin, tar, and textile; and “waste wax process” or “waste mold casting,” because the mold is destroyed to unveil the cast item.
Casts can be made of the wax model itself, the direct method; or of a wax copy of a model that need not be of wax.
Archeologists have found castings – thousands of years old. The basic principle of the process has remained unchanged, although many new techniques have been developed. The most significant of which was the use of molds from which many waxes could be made and the ceramic shell process gave a high-quality casting.
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History of Bronze
Bronze was significant to any culture that encountered it. It was one of the most innovative alloys of mankind. Tools, weapons, armor, and various building materials like decorative tiles made of bronze were harder and more durable than their stone and copper predecessors. Initially, bronze was made out of copper and arsenic to form arsenic bronze. It was only later that tin was used, becoming the sole type of bronze in the late 3rd millennium BC. Tin bronze was superior to arsenic bronze in that the alloying process itself could more easily be controlled (as tin was available as a metal) and the alloy was stronger and easier to cast. Also, unlike arsenic, tin is not toxic.
The earliest tin-alloy bronzes date to the late 4th millennium BC in Susa and some ancient sites in Luristan and Mesopotamia.
Copper and tin ores are rarely found together (exceptions include one ancient site in Thailand and one in Iran, so serious bronze work has always involved trade. In Europe, the major source of tin was Great Britain’s deposits of ore in Cornwall. Phoenician traders visited Great Britain to trade goods from the Mediterranean for tin.
Bronze is widely used for casting bronze sculptures. Many common bronze alloys have the unusual and very desirable property of expanding slightly just before they set, thus filling in the finest details of a mold. Bronze parts are tough and typically used for bearings, clips, electrical connectors, and springs.
Bronze also has very little metal-on-metal friction, which made it invaluable for the building of cannons where iron cannonballs would otherwise stick in the barrel. It is still widely used today for springs, bearings, bushings, automobile transmission pilot bearings, and similar fittings, and is particularly common in the bearings of small electric motors. Phosphor bronze is particularly suited to precision-grade bearings and springs. It is also used in guitar and piano strings.
Bronze is typically 88% copper and 12% tin. Alpha bronze consists of the alpha solid solution of tin in copper. Alpha bronze alloys of 4–5% tin are used to make coins, springs, turbines, and blades.
Commercial bronze (otherwise known as brass) is 90% copper and 10% zinc and contains no tin. It is stronger than copper and it has equivalent ductility. It is used for screws and wires.
Unlike steel, bronze struck against a hard surface will not generate sparks, so it (along with beryllium copper) is used to make hammers, mallets, wrenches and other durable tools to be used in explosive atmospheres or in the presence of flammable vapors.
Indian Hindu artisans from the period of the Chola empire in Tamil Nadu used bronze to create intricate statues via the lost wax method with ornate detailing depicting the Gods of Hinduism mostly, but also the lifestyle of the period. The art form survives to this day, with many silpis, and craftsmen, working in the areas of Swamimalai and Chennai.
In antiquity, other cultures also produced works of high art using bronze. For example: in Africa the bronze heads of the Kingdom of Benin, in Europe; Grecian bronzes typically of figures from Greek mythology, in east Asia; Chinese bronzes of the Shang and Zhou dynasties – more often ceremonial vessels but including some figurine examples.
Bronze continues into modern times as one of the materials of select choice for monumental statuary.
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