A Brief History of Bronze
and the Lost Wax Process
Bronze was first cast in China about 1,700 BC. Most of these castings were vessels used for ancestor worship, often engraved with the names of ancestors, or for commemoration of important events and intended as family heirlooms, now treasured as some of the most beautiful objects ever made by man. In the southern Chinese province of Hubei a set of bronze chime bells, inlaid with a filigree of gold inscriptions, dating to circa 500 BC, was recently discovered. The set consists of 65 bells, large enough to fill the stage of a modern recital hall, and encompasses 5 octaves, a greater range than many contemporary musical instruments.
In these early years the proportion of copper to tin varied from 67% to 95%. An 11th-century Greek manuscript found in the library of St. Mark's, Venice, Italy describes an alloy consisting of one pound of copper to two ounces of tin (around 89% copper), approximating that later used in the production of bronze gunmetal. Whilst less malleable than pure copper the alloying with tin makes it more fusible (easier to melt) and therefore ideal for casting. It is also much harder than copper and pure iron and considerably more resistant to corrosion than iron, making it ideal for outdoor use such as garden ornaments or fountains. Nowadays most commercial sculptures are cast using an alloy of copper, a small proportion of tin and additional metals such as zinc allowing sculptures to be available at lower cost. Sometimes known as "yellow bronze" this the bronze we use for casting most of our sculptures.
It is its unique casting properties that have assured bronze its continued popularity in cast sculptures. As the molten bronze solidifies, it expands, assuring accurate reproduction of every detail in the mould. During the cooling down period it contracts slightly, allowing removal from the mould. Bronze sculpture is often esteemed for the natural patina that forms over time as the surface of the bronze tarnishes. This thin, uniform patina of green and blue copper compounds also provides a measure of protection to the underlying metal.
In ancient Greece bronze was used for producing vases, statues and large-scale sculptures as well as protective helmets used in battle. In the Middle Ages churches and cathedrals, for doors, vessels, candlesticks, reliquaries, and other religious utensils, used bronze extensively. Common in households, up to the 19th century, were bronze basins and ewers, candlesticks, chandeliers and furniture fittings.
In the 16th century when the Spanish began the colonization of the Philippines they were probably quite surprised to discover that Filipino technology was not so far behind their own with the Filipinos manufacturing their own small, portable bronze cannons. By the 16th century bronze cannons were so valuable that they were the first to be salvaged from shipwrecks.
Using the original sculpture a rubber-based mould is formed and the inside coated with melted wax to the desired thickness of the bronze. Depending on the size and design of the sculpture the mould may be cut into sections and brazed (a technique similar to welding) together prior to finishing.
Once the wax has hardened the rubber mould is removed and the inside of the wax shell filled with a heat resistant mixture of plaster, sand and water, this is known as the “core” and is suspended within the mould by metal pins.
Once the plaster hardens and all the wax has drained away it is removed from the kiln and molten bronze poured, through the ducts, into the hollow left by the wax. Once the bronze has cooled the plaster shell is chipped away and any imperfections repaired, the sculpture is then ready for hand polishing and finishing.