The Jewelry Casting Process
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Definition
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Casting is the process where liquid metal is forced into a mold and cools into a particular shape. Jewelry casting is often accomplished with lost wax casting, a process at the center of handcrafted jewelry manufacturing. Said to be invented by Leonardo da Vinci, lost wax casting is a process which uses wax models to create the molds into which gold, silver and other metals can be cast. It has been used by jewelry makers for centuries to create rings, earrings, pendants, charms and many other pieces.
Wax Models
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The wax models used for lost wax casting can be hand carved or produced by wax injecting. Hand carving is preferred for special pieces and can be accomplished using a variety of types of wax.
Wax injecting is the process of creating a mold to generate multiple wax models of the same piece. It is used when more than one of a given piece is wanted as the wax model is destroyed in the casting process.
The desired pattern is pressed into clay in a flask with a sprue attached. The sprue creates a channel for the wax or metal to pass into the mold. The flask is closed and a silicon mixture added. Once sufficient time has passed for the mixture to cure, the flask is opened and the clay removed. The original pattern is placed into the now rubber half and the process is repeated to complete the second half of the mold.
Once the rubber mold is complete, wax is heated and injected into the mold to create the wax models needed for lost wax casting.
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Lost Wax Casting
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The wax model is set on a rubber base, using a sprue and enclosed in a flask. The flask is filled with investment, a plaster-like material which must be mixed and placed in a vacuum chamber prior to pouring in the flask. The vacuum removes air bubbles which can cause defects in the mold, affecting the final metal piece to be cast.
The investment with the wax model inside is placed in the vacuum and then allowed to set up for a period before it is baked in an oven. This step is known as the "burn out cycle." The wax model melts and evaporates--it is lost, which is where the name "lost wax casting" originates.
The investment is now the mold into which molten metal will be cast. Casting into the mold can be accomplished with steam, vacuum and centrifugal force.
Finishing
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Once the metal has been cast into the mold, it is allowed to cool briefly. The mold is then dunked into cold water. The water melts the investment, leaving only the cast metal piece. The sprue must be cut from the piece. The piece is filed and polished into its finished form.
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