![]() ![]() 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 model-maker may reuse the mould to make multiple copies, limited only by the durability of the mould. This hollow wax copy of the original model is removed from the mould. With this method it is more difficult to control the overall thickness of the wax layer. 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. Another method is to fill the entire mould with molten wax and let it cool until a desired thickness has set on the surface of the mould. This is repeated until the desired thickness is reached. ![]() Once the mould is finished, molten wax is poured into it and swished around until an even coating, usually about 3 mm ( 1⁄ 8 inch) thick, covers the inner surface of the mould. Sometimes many moulds are needed to recreate the original model, especially for large models. If there are long, thin pieces extending out of the model, they are often cut off of the original and moulded separately. Most moulds are made of at least two pieces, and a shim with keys is placed between the parts during construction so that the mould can be put back together accurately. The outer mould can be made from plaster, but can also be made of fiberglass or other materials. Inner moulds are usually made of latex, polyurethane rubber or silicone, which is supported by the outer mould. The rigid outer moulds contain the softer inner mould, which is the exact negative of the original model. A mould is made of the original model or sculpture. Wax and oil-based clay are often preferred because these materials retain their softness. An artist or mould-maker creates an original model from wax, clay, or another material. These are the steps for the indirect process (the direct method starts at step 7): Process Ĭasts can be made of the wax model itself, the direct method, or of a wax copy of a model that need not be of wax, the indirect method. (In modern industrial use, the process is called investment casting.) Variations of the process include: "lost mould", which recognizes that materials other than wax can be used (such as tallow, resin, tar, and textile) and "waste wax process" (or "waste mould casting"), because the mould is destroyed to remove the cast item. The steps used in casting small bronze sculptures are fairly standardized, though the process today varies from foundry to foundry. Lost-wax casting was widespread in Europe until the 18th century, when a piece-moulding process came to predominate. Other examples from somewhat later periods are from Mesopotamia in the third millennium BC. Cast copper objects, found in the Nahal Mishmar hoard in southern Israel, which belong to the Chalcolithic period (4500–3500 BC), are estimated, from carbon-14 dating, to date to circa 3500 BC. A copper amulet from Mehrgarh, Indus Valley civilization, in Pakistan, is dated to circa 4,000 BC. The oldest known examples of this technique are approximately 6,500-year-old (4550–4450 BC) and attributed to gold artefacts found at Bulgaria's Varna Necropolis. Intricate works can be achieved by this method. Lost-wax casting – also called investment casting, precision casting, or cire perdue ( French: borrowed from French) – is the process by which a duplicate sculpture (often a metal, such as silver, gold, brass, or bronze) is cast from an original sculpture. The sprue will be cut away and the final shape polished On the left is an example of a rubber mould, often used in the lost-wax process, and on the right is the finished bronze sculpture. In the next step (not shown), the mould is heated in an oven upside-down and the wax is "lost" Step 5: Liquid bronze at 1200☌ is poured into the dried and empty casting mould Step 5: the bronze cast, still with spruing attached. ![]() The core is also filled with fire-proof material. (The mould is shown here with a solid cast in plaster) Step 3: From this rubber mould a hollow wax or paraffin cast is made Step 4: The hollow paraffin apple is covered with a final, fire-proof mould, in this case clay-based, an open view. Step 1: A model of an apple in wax Step 2: From the model a rubber mould is made. Process by which a duplicate metal sculpture is cast from an original sculpture
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