How to Cast Bronze Sculptures With Lost Wax

Lost wax casting is often used for making bronze sculptures of human figures.

Lost wax casting is an old method for making bronze sculptures. The process has been used since the third century BC. The casting method remains essentially the same as it did back then, with modern refinement of its details. It was used by the ancient Chinese, Indians and Egyptians to cast ceremonial and religious images and by Classical Greek and Roman artists who used lost wax casting to make fine art statues and figurines. Fine portrait heads were cast by African tribal sculptors from the 1100s to the 1400s. Also called cire perdue, the technique remained prevalent in Europe until the 1700s. Lost wax bronze casting is still practiced on a small scale in the present day.

Things You'll Need

• Drawing materials
• Paper
• Bronze
• Wax
• Modeling clay
• Silicone rubber
• Plaster of Paris
• Ceramic materials
• Kiln
• Blast furnace
• Crucible
• Grinder
• Cauldron

Instructions

1. Draw thumbnail sketches of your ideas for a bronze sculpture. Draw details and compose the overall design of the piece. Work from life or from reference photographs for your preparatory drawings. Sculpt the original model for your bronze using wax or oil-based modeling clay. Build it freehand or form it around a wire or wooden armature, which is an internal skeletal framework. Finish the maquette or model, adding all of the textures and details you want in the final work.

2. Cover the entire model with a coat of silicone rubber for the soft inner layer of the negative mold. Wait until the rubber dries and hardens. Mix a batch of Plaster of Paris with the amount of water needed to make enough for the size of your project. Cover the rubber surface with a layer of plaster to support it and remove the rubber and plaster mold jacket in two sections. Make several sets of molds for casting multiple copies of the sculpture.

3. Melt the wax by heating it to 210 degrees Farenheit. Pour it into the mold. Build up several even layers against the rubber. Roll the mold around until the wax hardens. Swish the wax around; don't leave the mold in one position or it'll dry unevenly. Remove the mold, leaving a hollow positive wax copy of the model. Attach solid wax sticks (spruing) to the wax pattern to form channels and vents for the bronze to flow through.

4. Dip the sprued wax pattern into a slurry of ceramic silica, then sift on fine silica sand grit to build up the layers of your outer ceramic mold. Dip and sift several times for a half-inch thick ceramic shell. Air dry the ceramic mold. Heat the mold in the kiln till the wax melts and runs out. Recover the lost wax for later use. Fire the negative ceramic mold in the kiln to harden it for the casting.

5. Pour some water through the ceramic mold to make sure it flows through the spruing, or vent tubes. Heat the mold in the kiln so that it won't shatter when you add the molten bronze. Put bronze ingots, (weighed out blocks of brass), or scraps into a graphite or stone crucible. Use a natural gas blast furnace to heat the bronze to 1700 degrees Fahrenheit until it completely melts. Pour it into the mold. Break off the ceramic mold to reveal the final positive version of your bronze sculpture.

Tips & Warnings

• Finish the sculpture by removing the sprues and seams with a grinder.

• Wear protective gear when working with molten metals.

References

• Wild Life Art: Lost Wax, Found Bronze
• Lotus Sculpture: Lost Wax Method