I can offer a foundry service to sculptors and individuals wishing to reproduce their work in bronze. The use of a large commercial foundry can be too expensive for the sculptor wishing to produce a one off or a small sculpture. I can usually provide this service much cheaper because my setup is small in comparison and I do not have the large overheads of a big foundry. I also have the advantage of not having to employ other people, and the expenses associated with this. I carry out all the stages myself, including producing the wax pattern, spruing, ceramic shell investment, casting and chasing. You can read about these stages in detail below. I specialise in casting smaller pieces up to about 30cm. However, larger pieces are achievable by producing the work in sections and TIG welding them together seamlessly using the same alloy as the casting, so that the join is completely invisible. Please contact me through the 'Contact Us' page to get a quote. Please provide as much detail as possible about the sculpture and your preferred method of communication an I will get back to you with a price.
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Casting a Bronze Sculpture |
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Lost-wax casting, sometimes called by the French name of cire perdue, is the process by which a bronze is cast from an artist's sculpture. It is an ancient practice, the process today varies from foundry to foundry, but the steps which are usually used in casting small bronze sculptures in a modern bronze foundry are generally quite standardized. • Wax. A mould is made of the original sculpture, molten wax is poured into it and swished around until an even coating, usually about 1/8 inch or 3 mm thick, covers the inner surface of the mould. This is repeated until the desired thickness is reached. Another method is filling the entire mould with molten wax, and let it cool, until a desired thickness has set on the surface of the mould. After this the rest of the wax is poured out again, the mould is turned upside down and the wax layer is left to cool and harden. With this method it is more difficult to control the overall thickness of the wax layer. • Removal of wax. This hollow wax copy of the original model is removed from the mould. The model-maker may reuse the mould to make multiple copies, limited only by the durability of the mould. • Chasing. Each hollow wax copy is then "chased": a heated metal tool is used to rub out the marks that show the parting line or flashing where the pieces of the mould came together. The wax is dressed to hide any imperfections. The wax now looks like the finished piece. Wax pieces that were moulded separately can be heated and attached; foundries often use registration marks to indicate exactly where they go. • Spruing. The wax copy is sprued with a treelike structure of wax that will eventually provide paths for molten casting material 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. This spruing doesn't have to be hollow, as it will be melted out later in the process. • Slurry.A sprued wax copy is dipped into a slurry of silica, then into a sand-like stucco, or dry crystalline silica of a controlled grain size. The slurry and grit combination is called ceramic shell mould material, although it is not literally made of ceramic. This shell is allowed to dry, and the process is repeated until at least a half-inch coating covers the entire piece. The bigger the piece, the thicker the shell needs to be. Only the inside of the cup is not coated, and the cup's flat top serves as the base upon which the piece stands during this process. Prior to silica, a mixture of plaster and fire-proof material such as chamotte was used. • Burnout. The ceramic shell-coated piece is placed cup-down in a kiln, whose heat hardens the silica coatings into a shell, and the wax melts and runs out. The melted wax can be recovered and reused, although often it is simply burned up. Now all that remains of the original artwork is the negative space, formerly occupied by the wax, inside the hardened ceramic shell. The feeder and vent tubes and cup are also hollow. • Testing. The ceramic shell is allowed to cool, then is tested to see if water will flow through the feeder and vent tubes as necessary.Cracks or leaks can be patched with thick refractory paste. To test the thickness, holes can be drilled into the shell, then patched. • Pouring. The shell is reheated in the kiln to harden the patches and remove all traces of moisture, then placed cup-upwards into a tub filled with sand. Metal is melted in a crucible in a furnace, then poured carefully into the shell. If the shell were not hot, the temperature difference would shatter it. The filled shells are allowed to cool. • Release. The shell is hammered or sand-blasted away, releasing the rough casting. The spruing, which are also faithfully recreated in metal, are cut off, to be reused in another casting. • Metal-chasing. Just as the wax copies were chased, the casting is worked until the telltale signs of the casting process are removed, and the casting now looks like the original model. Pits left by air bubbles in the casting, and the stubs of spruing are filed down and polished. |
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