Description
There are several methods and procedures for casting bronze. Below is an attempt to summarize the basic steps. A model is made, usually of wax. However, if a rubber mold is used, it can also be made of clay, plaster, plastic, or even wood or stone. The wax used for this is usually casting wax, paraffin, or modeling wax. For small wax models, the caster can proceed directly to the next step. For larger models, or for models made of clay or plaster, for example, a hollow wax model must first be created. To do this, the caster usually makes a rubber mold with a plaster support cap, which ensures that the rubber mold retains its shape. Various materials, such as casting wax or plaster, can be poured into this rubber mold at relatively low temperatures. In this case, a hard wax cast is required, which is already the thickness of the final bronze. Above a certain thickness, it becomes difficult to cast bronze solidly due to uneven shrinkage of thicker and thinner parts. The caster pours liquid wax into the rubber mold until a layer of the correct thickness has solidified. The remainder is poured off, creating a hollow wax cast. This (hollow) cast is provided with wax projections that will later serve as sprues for the bronze supply and vents for the removal of air from the mold. The wax cast, including the sprues, is covered inside and out with a refractory material. This can be a mixture of plaster and fireclay or another shrink-resistant and refractory material. Stainless steel core supports ensure that the distance between the core and the outside remains consistent. The finished cast is heated for a long time in a kiln to melt out the wax and remove all moisture from the mold, and if it is made of plaster, also all chemically bound water. A dry mold is now created with a cavity in the shape of the model and sprues. Liquid bronze is poured into this cavity. After cooling, the channels are sawn away and the casting is finished: burrs and protrusions are ground away, and holes and unwanted cavities are hammered or welded shut. This protects against oxidation and enhances the appearance.
