A two-part mould is made from the clay so that each half can be filled with wax and put back together accurately. To preserve the fine details of the clay’s surface, silicon rubber is applied onto the clay.
This is supported by a plaster layer which ensures both halves of the mould create a tight fit.
Lost-wax Bronze casting has its roots in antiquity, yet has not changed in thousands of years.
Sometimes called by the French name of "cire perdue" meaning "lost wax".
Removal of wax & touching up
This hollow wax copy of the artwork is removed from the mould.
The hollow wax copy is then "dressed" to hide any imperfections including the seam line. A wax "foot" is added so that it can be attached to a base. The signature plus edition number with date are etched into the wax. The wax now looks like the finished bronze in every detail. A separate wax is required for each bronze edition to
Spruing & Investment
The wax copy is "sprued" with a tree–like structure of wax that will eventually provide paths for molten bronze to flow and air to escape.
The carefully planned spruing usually begins at the top with a wax "cup", which is attached by wax cylinders to various points on the wax copy.
The "sprued" wax is covered in a mixture of plaster and crushed ceramic (investment). The process is repeated until a coating of 10cm covers the entire piece.
Burnout, pouring & release
The invested wax is placed cup–down in a kiln for at least 36 hours. The melted wax can be recovered and reused, although often it is simply burned up, hence the term "cire perdue" (lost wax).
Now all that remains of the original wax is the negative space that it once occupied within the investment material. The feeder and vent tubes and cup are also hollow.
The investment is placed cup–upwards into a tub filled with sand. Bronze is melted in a crucible in a furnace to 1200 degrees C, then poured carefully into the investment. The bronze–filled investment is allowed to cool and can be opened with half an hour of pouring.
The investment material is hammered away, releasing the rough bronze. Now one can see if the casting is successful and at this stage it is customary to open a bottle!
The spruing tubes, which are also faithfully recreated in metal, are cut off, to be reused in another casting. The bronze is worked until the telltale signs of casting are removed, and the sculpture again looks like the original artwork. Pits left by air bubbles in the molten bronze are filled, and the stubs of spruing filed down and polished. The foot of the bronze is levelled and drilled, ready for the base.
The bronze is now ready for colouring (patination). This is an age–old technique that mimics the patina′s of ancient bronzes and many foundries keep their recipes under lock and key! I prefer to use hot patination which gives me a very stable and even colour.
The bronze is heated with a blow torch and acids stippled onto the surface to oxidize the metal. After the patina is applied, a very light coating of pure bees wax seals and protects the bronze.
The bronze is firmly secured to a marble or wooden base that has been made for the unique sculpture. The sculpture is finished and ready for delivery with an authentication certificate.