John Bassi > Bronzing

The Bronzing Process

Once an idea has set itself, mostly gained from an actual event observed during work in the field, rough pencil drawings are made in order to preserve the concept. Research can often take more time than the work itself and will include photographing the subject, in the wild, from as many angles as possible, mostly from the helicopter. An armature (or framework) is then made out of wood and mild steel, which will support the clay model. This original model is sculpted out of various materials, for example clay, wax and wood.

Moulding

Once the original model is completed, which can take up to 6 weeks; moulds are taken by dividing the original piece into sections using silicone rubber, fiberglass and plaster of Paris. The original is then removed from the mould and destroyed, leaving only the mould. Molten wax is poured into the mould producing a replica of the original, which is then repaired and touched up. Wax runners and risers with a wax funnel are attached to the wax replica in such a way as to prevent air locks occurring when the molten bronze is poured into the final ceramic shell. The wax replica with runners is dipped into a special mixture of sand and ceramic slurry until it is at the desired wall thickness. The “lid” of the funnel is cut off and the ceramic/wax replica is fired in a kiln until the ceramic has set and the wax burned out completely, leaving a ceramic shell.

Bronzing

Bronze ingots are melted in a crucible using a furnace heated to 1300 degrees centigrade; this molten bronze is then poured into the funnel of the ceramic shell, finding its way to all the intricate appendages of the replica, via the runners.

After a precise time, the excess molten bronze from the core is discarded out the replica, leaving a thin wall of bronze approximately 4 to 5 mm thick. This procedure is crucial since it is not possible to cast solid bronze without facing enormous shrinkage, cracking and deformity of the piece, not to mention the weight. Once the bronze has cooled completely, the ceramic shell is chipped off. The runners, funnel and any defects are cut off the bronze which is then ready to be worked. Extra pieces are welded onto the sculpture which is then sand blasted, worked, polished and buffed.

Finishing Touches

The raw bronze sculpture is prepared for the patina, a process involving the application of heat and various acids, causing the bronze to undergo an oxidization process, until the desired colouring is obtained. The sculpture is then sealed with wax which preserves the patina and brings out the life of the sculpture, which must now be mounted onto an appropriate base made of wood, stone, granite or marble.

Images from the Bronzing Process