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To understand how Bronze Sculptures are created we have put this article together to help you understand the Lost Wax Casting process for Bronze Statues.
The first step for this bronze casting process is to create an original sculpture design. Charles, the sculptor on our website www.DimensionsThruArt.com begins his pieces with a wire model and then covers them with clay. He adds clay and smoothes out the clay until the figure is the image he imagined for his bronze sculpture. Most of his models start at approximately 12 inches.
A plaster mold is then made from the clay model. Plaster is used to cover the clay. Several layers of plaster are put on the clay to form a ½ inch thick coating. After the plaster has dried, the mold comes apart. The molds are then used to reproduce his pieces in wax. Molten wax is poured into the mold, after letting the wax seep into all the crevices of the mold the wax is poured back out. When the wax is cooled, the wax mold is removed from the plaster. The wax figure is then finished with kerosene and a special sanding screen until the form is smooth.
The wax model is then attached to a gating system which will allow the molten bronze to flow to where the wax piece of sculpture once was. Gates or sprues made from rods of wax and a venting system is made the same way to move air and other gasses out of the mold when it is filled with hot bronze. Once the model is set up with its gates and vents, it is surrounded with ceramic slurry; this is done by dipping the model into the slurry. Special dry aggregate (silica sand) is then applied to the wet slurry by using a fluidized bed which blows the dry particles around in a confined space, covering the wet areas until no more will adhere. The coated form is then hung to dry. After drying, another layer of wet and dry material is applied. This process is repeated until a sufficient thickness is built up. This material will cover it smoothly and withstand high temperatures when baked.
Once the ceramic shell has dried and hardened, the forms are placed in a kiln and slowly heated to between 1000 and 1250 F, and held at that temperature until all wax residues have disappeared. The place where the wax was, is now a void – hence the “lost wax” method for this process. The metal is then melted to a temperature of 1750 F and the molds are filled with liquid bronze. The form is allowed to cool, and the ceramic mold is broken away, revealing the metal sculpture. The gates and vents, now bronze must be cut off using a plasma cutter. Sand blasting is then done to remove all of the shell.
Next is the assembly of the sculpture. The individual parts are welded together and then grinded down to form the original sculpture. Grinding, chasing, and hand sanding will get the sculpture ready to patina. The bronze is now treated with chemicals and heat to give it the color the artist has chosen. After the sculpture has cooled a carnauba wax is applied to protect the patina. The wax is brushed on and then buffed off with a soft cloth. The sculpture is mounted on its base and engraved with the artists name and number of edition.
This model can now be used to make larger additions of the same sculpture by using an enlarging tool called a panagraph machine. The process is basically the same for the larger piece. Instead of wire for the model, rebar is used to form the metal armature the clay will be formed around.
We hope this article was helpful. Bronze casting for sculptures is a very time consuming process but the museum quality bronze statues are well worth the time and effort. Please let us know if you have any additional questions or needs by contacting us.
Lost Wax Casting for Bronze Sculptures