Sculpting  & Bronze Lost Wax Process

It all starts with Pen being struck by the beauty of something seen and then drawing a sketch or taking a photo.

The original is usually sculpted in pottery clay over many days and sometimes months.

A silicone rubber mold is made by brushing on a viscous, platinum-catalyzed liquid. Many coats are applied until the necessary thickness is achieved.

Plaster is poured over the silicone encased sculpture to create a "mother mold," which will support the floppy rubber when the wax copy is made.

When the plaster has hardened, everything is flipped over and the clay positive is removed. The plaster-supported, silicone mold is the exact negative of the original sculpture. This will allow copies to be made out of wax.

Molten wax is carefully brushed onto the silicone rubber mold to create the wax copy. Many coats are needed to achieve the  uniform thickness required for a bronze .

When the wax has cooled, the rubber mold is gently pealed away and the wax copy is revealed. 

Excess wax is trimmed and any imperfections in the wax copy are carefully fixed in a process known as "chasing." 

The wax is then taken to the foundry to be cast. First they will attach wax bars and a cup which will be the channels for the liquid bronze to flow. This is called spruing.

The wax is first dipped into a colloidal silica slurry and then sprayed with a very fine silica, which is allowed to dry. Another coat is applied and the process is repeated over the course of many days until the shell is thick enough to hold the molten bronze.

Then the shells are loaded into the blast furnace. There the wax is melted out at 1300° F and the created void in the heat-hardened shell becomes the mold for the bronze.

The shell mold is checked to see if it will hold liquid (water) and is patched with thick refractory cartable-mortar where it's necessary.

On the pour day, the shells are reheated to bring them up to temperature and to the harden patches. The bronze ingots are melted at 2000° in a silicon-carbide crucible.

The hot shells are tied to a bar with their cups up in a tray with a bed of sand. Then the glowing crucible is hoisted up and out of the kiln.

Using the hoist, the crucible is maneuvered over to the line of shells.  Moment of truth - Molten Bronze is poured into the cup of each of the hot shells.

The new Bronzes in their shells are brought outside to cool and then untied. When cool enough to handle with heavy gloves, the foundry worker chips off most of the shell with a ball pein hammer. 

Some shell bits stick to the bronze that can not be safely removed with the hammer. (Notice the sprues and cup are still attached) Foundry worker sand-blasts the remaining shell off in special cabinet.

The welder cuts off the sprues, flattens the bronze, and attaches hardware to hang the plaque. Although I often have the foundry do all the metal work, I will chase this piece myself.

Basic grinding smooths edges and large areas and then small rotary tools and scribes perfect the details on the sculpture.