Bronze Zebras by Antoni La Porta 2008

There are multiple methods and procedures possible for casting bronze. The following attempts to provide a summary of the basic steps. A model is made, usually from wax. But if a rubber mold is made, it can also be made from clay, plaster, plastic, or even wood or stone. The wax used for this is usually casting substance, paraffin, or modeling wax. With small wax models, the caster can immediately proceed to the next step. For larger models or for models made of, for example, clay or plaster, a hollow wax model must first be created. To this end, the caster usually makes a rubber mold with a gypsum support cap, which ensures that the rubber mold retains its shape. In this rubber mold, various materials can be cast at relatively low temperatures, such as casting wax or plaster. In this case, a cast of hard wax is needed, which is already at 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 right thickness has solidified in the mold. The rest is poured out, creating a hollow wax cast. This (hollow) wax cast is provided with wax protrusions that will later serve as casting channels for the supply of bronze and venting channels for the discharge of air in the mold. The wax cast, including channels, is covered inside and out with a refractory mass. This can be a mixture of plaster and chamotte or another shrink-resistant and fireproof material. Stainless steel core supports ensure that the distance between the core and the outer side remains consistent. The completed mold is heated for an extended period in an oven to melt out the wax and remove all moisture from the mold, and if it is made of gypsum, also all chemically bound water. A dry mold has now formed with a cavity in the shape of the model, complete with casting channels. Liquid bronze is poured into it. After cooling, the channels are sawed away and the casting is finished: burrs and protrusions are ground away, and holes and unwanted cavities are hammered or welded shut. For protection against oxidation and for aesthetic purposes, a patina layer is often applied to bronze castings, especially in sculptures, using chemicals, a process known as patination.