Home: Classic Sculpture by Susan Wagnerlittle girl sculpturebird sculpture

Outline of the Steps

  1. Armature
  2. Sculpting
  3. Mold Making
  4. Rubber Mold
  5. Mother Mold
  6. Remove Molds
  7. Wax Casting
  8. Chasing Wax
  9. Spruing
  10. Slurry
  11. Shell Burn-out
  12. Shell Preparation
  13. Melting & Pouring Bronze
  14. Shell Removal
  15. Sprue Removal and Sandblasting
  16. Welding
  17. Metal Chasing
  18. Final Sandblasting
  19. Patination
  20. Installation

The Bronzing Process

  1. Armature - The sculpture’s framework, known as the armature, is built. Armatures provide structure and stability for a piece and are often made of steel for larger sculptures and aluminum wire for smaller pieces.
  2. Sculpting – The artist applies clay directly over the armature to create the sculpture.
  3. Mold Making – After a clay model is complete, it is sealed and a mold release agent is applied so a mold can be removed without damaging the original sculpture.
  4. Rubber Mold – The sculpture is first covered with a thin layer of rubber. After the first rubber layer sets, additional coats of rubber will be applied. At this time keys are also set to facilitate alignment after the mold is separated into halves. Simple, small sculptures may require just one mold while large sculptures or those that show movement may require several molds. The size and movement of a piece determines how many molds will be created and, therefore, how long this part of the process takes. After the rubber sets, a mold release agent is applied to the surface and the mold is cut into halves.
  5. Mother Mold – Now the back-up mold, also known as the Mother Mold, is created by covering the rubber mold with strips of hemp that have been dipped in a plaster mixture.
  6. Remove Molds After the plaster has set, both halves of the Mother Mold and then the rubber mold are removed to reveal the original clay sculpture. The rubber mold is then cleaned to remove debris from the original sculpture. During the mold making process the original clay sculpture was destroyed and after this step is complete the remains of the original clay sculpture is discarded.
  7. Wax Casting – The first coat of melted wax is brushed into the rubber mold to capture the fine details of the artist’s original sculpture. Then the rubber mold halves are put back together and sealed. As a cooler wax is poured into the hollow mold, the mold is rotated to distribute the wax evenly. After the wax cools, the rubber mold is removed from the wax casting.
  8. Chasing Wax – The wax casting is now refined with the goal of replicating the original clay sculpture. This process includes removing the seam lines or air bubbles created during the waxing process.
  9. Spruing – Spruing is the process of creating a treelike structure of wax rods and a cup on top of the wax mold. The wax rods provide paths for the molten bronze to flow and for air to escape the mold.
  10. Slurry – The wax casting is dipped into a liquid binder material (slurry) and covered with a fine ceramic shell. After the first coat dries, the process is repeated. Then, a courser shell is added. The size of the statue determines how many coats of shell are necessary, a larger sculpture requires a thicker shell.
  11. Shell Burn-out – After the shell dries, holes are drilled into the shell. These holes will allow the wax from the wax casting to escape when the shell is placed in a kiln and baked.
  12. Shell Preparation – After the shell is baked, the wax evacuation holes are patched and any hairline cracks are fixed. Then the shell is preheated in the kiln to prepare it for the bronzing.
  13. Melting & Pouring Bronze – In a furnace, bronze ingots are melted to the correct pouring temperature, which is determined by the artwork’s unique configuration, thickness, and size. Then the bronze is taken from the furnace and poured into the shell molds, which have already been taken from the kiln and put into a vat of sand.
  14. Shell Removal – Shortly after the bronze is poured, the piece is removed from the sand and the shell is knocked off, revealing the unfinished bronze casting.
  15. Sprue Removal and Sandblasting – Now the sprues are cut off and the piece is sandblasted to remove any remaining pieces of the ceramic shell and to unify the color of the surface.
  16. Welding – Large bronze sculptures are cast in several pieces, which are now fitted together and welded in place.
  17. Metal Chasing – The bronze surface is refined to eliminate signs of welding or other imperfections.
  18. Final Sandblasting - The sculpture is sandblasted again to eliminate any discoloration on the surface of the bronze that could have resulted from atmospheric conditions or oil stains from handling. This step also slightly roughens the bronze surface to help the patina stick to it.
  19. Patination - Patination is a process that can embellish a bronze sculpture’s color and texture. A variety of chemicals can be sprayed, brushed, or heated onto the bronze to achieve a different color or look. After the patina is applied, the sculpture is coated with wax or an enamel sealant and then waxed to help protect the patina against degradation from atmospheric conditions.
  20. Installation – Necessary artisans, craftsmen, and professional installers are employed to install larger sculptures. Smaller sculptures may need a base added if they are not free standing.