How to Make Clay Molds for Bronze Art

With clay molds for bronze casting, you can make a wide variety of bronze art.

Bronze casting has been around since the early Bronze Age. According to professor Richard Cowen at UC Davis, bronze artifacts have been found at Ur and other Mesopotamian cities dating from about 3000 BC. Back then, bronze was primarily cast for weapons and tools. Now bronze is cast for art and collectibles as well as machinery. The process hasn't changed much; the method of lost wax casting using wax and clay molds remains a time-honored method for casting bronze.

Things You'll Need

• Original sculpture
• Clay
• Paintbrush
• Silicone rubber
• Plaster
• Wax
• Wax or clay modeling tools
• Ceramic kiln

Instructions

Making the Clay Mold

1. Lay the original sculpture for reproduction down on a flat surface. Use clay to build a barrier around the original halfway up its sides so that only the top half of the sculpture is visible.

2. Paint on the rubber to create a negative. Paint several layers of silicone rubber over the half of the original. Allow rubber to dry according to its manufacturer's directions before applying the next coat. Continue until all the areas of the original are covered with a 1/4-inch thickness of rubber.

3. Paint rubber on the other side. Lay the first half of rubber aside, flip the original over and follow Step 2 for the other side. The whole process should take about a week depending on drying time and size of the piece.

4. Create the mother mold. The rubber negatives need a stiff carrier so they can hold the form once the original is removed. Build up a casing over the rubber by applying plaster in layers over the rubber to form a thick shell. Allow the plaster to dry between layers. The plaster shell should completely encase the rubber negative. When the shell is dry, remove the original sculpture and rejoin the two sections of the mother mold.

5. Make the wax positive. Flip the plaster mother mold upside down to expose the pouring channel. Melt the wax according to its manufacturer's instructions and pour enough into the negative mother mold to give a single coating. Allow the wax to dry. Repeat the process until the wax layer is 1/4 inch thick.

6. Check the wax for accuracy. Remove the mother mold and rubber negative to reveal the wax positive. Remove any imperfections in the wax duplicate of the sculpture that formed during pouring with your clay or wax modeling tools.

7. Create the negative clay mold. Use small pieces of clay to completely cover the wax copy. Make sure to push and fill every space on the copy to produce an accurate negative. Allow drying time for the clay mold and drill out small holes in the backside of the mold. These holes allow wax and air to escape during the firing process.

8. Fire the ceramic mold. Place the ceramic mold in the kiln and fire at 1500 to 1600 degrees F. The wax will burn out of the mold and produce a perfect negative.

9. Plug and re-fire the ceramic mold. Use bits of the clay to plug up the holes once the ceramic has cooled. Re-fire the mold at 1500 to 1600 degrees F so the form is hollow and without holes.

10. Remove the mold from the kiln and allow to cool before pouring the bronze.

Tips & Warnings

• For larger sculptures, use canvas or burlap strips mixed in with the plaster to make a more durable mother mold.

• Be sure to allow the kiln to cool down before attempting to take out any of the clay. You can burn your hands and the clay needs a slow regulation of temperature so it doesn't crack.

References

• UC Davis Department of Geology's Richard Cowen: The Bronze Age

Resources

• University of California, San Diego: Ethnoarcheology in India