How to Make a Mold for Sculptures

Eagle sculpture.

Mold making was traditionally used to create bronze sculptures. Famous artists from the Italian Renaissance age through modern times have employed this method of first creating a clay model, building a mold around it and then pouring the final material inside the mold to make the final sculpture. Artists today often use new casting materials, such as concrete or polyester-resin compounds, to form their sculptures rather than bronze.

Things You'll Need

• Wood or wire
• Clay
• Plaster powder
• Bucket
• Brush
• Knife
• Petroleum jelly
• Shellac
• Paste wax
• Silicone spray

Instructions

1. Build an armature for your sculpture. Form the inner skeleton of your piece with wood or wire. Attach it securely to a wood base. The size and shape of the armature depends upon the sculpture you are creating.

2. Build the model of your sculpture from clay. Gradually add water-based clay to the armature to create the three-dimensional piece.

3. Roll out slabs of clay to create a barrier or fence around the model. The clay should be rolled into a 1/2-inch-thick slab and then sliced into 1-inch-wide strips. Press the strips onto the mold, adhering them securely.

4. Mix the plaster powder according to the manufacturer's directions. Remember that plaster is always added to water, not the other way around. Brush a layer of fluid plaster on the model. This thin coat will capture all the small details and help to catch any air bubbles that might go unnoticed and mar the surface. The plaster in the bucket thickens as it sits. Add a layer of this thickened plaster to the model. Continue to apply until it is approximately 1 inch thick. Trim the outside of the plaster as it sets up with a knife so that the surface is smooth.

5. Remove the fence around the mold after the plaster has set. The plaster will feel warm as it begins to set. It generally takes 20 minutes. Apply the next section of fence to the model and repeat the application of plaster, starting with a fluid layer and gradually building it up.

6. Coat the edges of the plaster mold sections with petroleum jelly. Before applying the last section of plaster to the mold, add a separator between the fence and the plaster.

7. Carefully pull the cooled pieces of hardened plaster from the clay model. Clean excess clay residue off the plaster by brushing the plaster with a wet paint brush. Patch any air pockets with fresh plaster.

8. Prepare the mold for casting by brushing on three coats of shellac to the interior of the plaster pieces. Once dry, apply paste wax evenly to the surface, followed by a spray of silicone spray. These precautions will keep the mold intact without chipping or breaking while casting.

Tips & Warnings

• Molds can also be formed around existing sculptures, rather than creating your own from clay. Follow the same procedure, apply the fence and plaster to re-create the object of your choice.

• Do not use any tools when adhering the fencing pieces to the model. Any marks made will show up in the final sculpture.

References

• "Crafts and Hobbies: A Step by Step Guide to Creative Skills"; William Finneran; 1979

Resources

• Borsheim Arts Studio: Bronze Casting Process