CREATION OF A BRONZE SCULPTURE

 

Jim Bridger Monument at Chamber of Commerce Building

Bozeman, Montana  

 

STEP 1:
 
MAQUETTE
& ARMATURE
 
STEP 2:
 
RUBBER MOLD

First, a miniature clay model called a maquette is created.  Once a pleasing composition is chosen, an armature of steel tubing, aluminum wire and styrofoam is built to support the larger than life-size original clay sculpture.

Once the original clay sculpture is completed, it’s cut into various pieces and a flexible latex rubber mold is painted over the clay capturing every detail of the sculpture.  A ridged plaster backing is then built over the rubber mold.

 
STEP 3:
 
WAX POURING

Hot wax is poured into the rubber mold at 225 degrees to produce a wax replica of the original clay sculpture.  Pieces larger than tennis ball size, must be cast hollow to prevent heat shrink as the metal cools.  Thus, several coats of wax are poured into the mold and then dumped out leaving a hollow 1/4” thick wax inside.

 
STEP 4:
 
WAX CHASING

Seam lines, where the mold was pulled apart and other imperfections in the wax model are removed. Various wax pieces (cut off for molding), may have to be reassembled together, matching the textures of the original sculpture.

 
STEP 5:
 
SPRUING

Wax spru bars, which will become channels where molten bronze will flow, are attached to the chased wax casting, which is then attached to a hollow wax cup.

 
STEP 7:
 
METAL POURING

Molten bronze is poured into the ceramic shell at 2100 degrees. Once the metal has cooled, the ceramic shell is chipped and sandblasted off the raw bronze casting.  The now metal sprue bars and cup are cut off of the casting.

STEP 9:
 
PATINA

The finished bronze is heated with a torch and liquid chemicals are applied with a brush. The metal absorbs the chemicals to create beautiful patinaed colors.

 
STEP 6:
 
CERAMIC MOLD

The sprued waxes are dipped into a liquid ceramic slurry (six coats) forming a mold around them. Once cured, they are placed in a burnout oven where the wax is melted from inside leaving a ceramic shell – thus the term “lost wax process”.

 
STEP 8:
 
WELDING &
     METAL CHASING

The bronze pieces are welded together forming the complete sculpture. Weld lines are removed and blended with various hydraulic grinders, sanding cones etc. to match the textures of the original sculpture.