During the Renaissance, sculptors worked around bronze using the lost-wax method. Basically, it involved pouring smelted bronze into a clay-wax mold with a low melting point. It's called "lost-wax" because the mold is destroyed during the process. Historians believe the practice began in Africa as early as the tenth century.
Today’s technology has given rise to more than one method of casting bronze. The lost-wax art still lives on as investment casting, while sand and centrifugal casting methods have also seen widespread use. Here's a breakdown of the three most common casting methods, which are also used to fabricate machine parts.
Not much has changed in investment casting from the lost-wax method. One of the differences is the mold used; whereas the early casters used beeswax or latex, investment casters today use a ceramic slurry. The ceramic coating allows the mold to withstand the molten metal but not without preheating the mold to 1,000o C first.
This casting method yields more intricate figures but suffers from a low production rate since, like the lost-wax method, the mold will be destroyed. One of the most widely-used types of sand for this process is green sand (not to be confused with greensand). This sand contains silica, clay, water, inert sludge, and anthracite.
Using centrifugal and centripetal forces, this casting method results in bronze pieces that are toughest on the surface. This is thanks to the rotational forces pushing the molten metal outward.