2015 Jan Willem van der Wal Bowen Island BC Bronze; Lost Wax Method (cire perdue) The lost wax (cire perdue) method: A sculpture made out of wax cast in a mold from grog and plaster which can be burnt away. The original wax structure is now gone and the mold holds a hollow negative of the sculpture. Into this mold the hot liquid bronze will be casted. After cooling down the mold itself has to be smashed /demolished to retrieve the sculpture in bronze. The bronze has to be cleaned from all kinds of abnormalities, created during the firing of the mold and casting the bronze. (air bubbles, small cracks turn in bronze too) Also the casting cup, support posts and vents must be removed. After cleaning the sculpture you can color it by fast oxidizing, using different chemicals and a torch. The finishing touch is made with some polish. Creating a bronze sculpture, step by step: Phase I Creative Using all kinds of materials which can burn, but mainly wax, you create the wanted sculpture. As wax is a weak substance (there are different kinds of firmness) you might reinforce the wax, using wood (branches), plastic, cloth,cardboard, etc. In fact everything that can burn will vanish during the burning process of the mold. Wax and other materials for the sculpture The sculpture in wax
Phase II Creating the correct flow for bronze This is the most important step in the process to create the sculpture. To enable a proper flow of the liquid bronze into the mold you should prevent airlocks and too narrow passages. Also great differences in thickness can cause failures in the final product due to uneven shrinking or cooling down speed. The wax structure must be connected to a casting cup / sprue gate and air vents to enable the bronze to flow properly through the hollow chambers. Also sometimes bypasses are necessary on the original structure. Casting cup/ sprue gate, vents and supports mounted (casting cup shown upside down) Phase III Mold making To form the wax structure in a mix of plaster and grog a form should be made. Metal sheet material is very good to create a flexible form. The grog and plaster (1:1) is mixed with clean water till it reaches the consistency of yogurt.
Plaster and grog (coarse) This liquid mix is poured along the wax structure into the form. About half an hour later the form can be removed and the mould is ready for firing in a kiln. The wax model in the form The form filled with grog/plaster mass Phase IV Burning out the wax The mold is placed in a kiln and burned out for about 24 hours up to 800 degr. Celsius. (1500 F) After cooling down a negative of the sculpture remains in the mold. Small particles remaining in the hollow part of the structure can be removed by vacuuming. Molds in the kiln The kiln
After firing the mold for about 24 hours, the mold, ready to cast the bronze Phase V Pouring bronze Melted bronze with a temperature between 1100 and 1200 degr. Celsius (2000-2200 F) is cast into the mold till the vents in the mold fill with bronze too. Smelting furnace with crucible
Bronze is an alloy of copper, tin and zinc (90% Co, 4% Sn, and 6% Zn) Pouring the bronze Bronze has cooled. Pouring cup and vents filled with bronze
Phase VI Cleaning the sculpture The mold can be broken and the bronze structure thoroughly cleaned using also a pressure washer. Sculpture after cleaning Sculpture after removing casting structure The casting cup / sprue gate, vents and other casting bypasses are removed using a saw, angled grinder, Dremel and chisels. Various tools to finish the sculpture
Small bronze cracks and bronze bullets can be removed using a chisel. Also a steel brush attached to an angled grinder can be used too. Phase VII The finishing touch After cleaning the sculpture is now in bronze. Using chemicals such as liver of sulphur, aluminum sulphate and copper nitrate to apply to the sculpture, using a torch gives the desired colors. Some chemicals react slowly in humid air and show their patina after some weeks. Clockwise top: copper carbonate, copper nitrate, liver of sulphur, copper acetate & coppersulfate. To deepen the effect of color, shoe polish can be applied and some spots brightened by polishing with a polishing machine.
Jan Willem van der Wal Bowen Island July 2014. The result: Take Off Amazon Mistake Walking together Growing The box
Movement Uranus Joep Kahn Take off Happy landing Seagull Eye catcher