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Technique

Lost wax casting

Lost wax casting is used to mould various types of metal into intricate pieces of jewelry and artistic sculptures.


The wax casting process starts with sketching out a preliminary drawing of the piece you have in mind. Then, the wax carver crafts a representation of the desired piece out of wax or clay, creating a pattern with the same intricate detail that will appear on the metal piece of jewelry in its final form.  The wax pattern is then attached to a "sprue base" which is made of durable rubber.  The rubber base with the wax model is then covered with a metal flask and investment is poured over it.


After the chunk of plaster has been allowed to dry it is then placed in a hot kiln. As temperatures rise, the wax within is melted and eradicated, hence the name "lost wax."  The result of this stage is a strong mould with a hollow opening in the shape of the original wax design.  In the kiln, the burnout times are anywhere from 5 - 12 hours. The flask is then taken out of the kiln and placed in the centrifuge.


Bits of silver and gold are ready to be melted. Sterling silver is an alloy of silver containing 92.5% pure silver and 7.5% other metals, usually copper. The minimum millesimal fineness is 925.  Fine silver (99.9% pure) is too soft for producing large functional objects, and in Sterling, the silver is usually alloyed with copper to give strength while preserving the ductility of the silver and high precious metal content. 


A crucible will be heated. When the crucible will be red hot, it will be placed in the centrifuge and the silver will be poured into it.  The crucible sits tightly against the flask which holds the negative impression made by the burned-out wax pattern.  When the metal is completely liquefied, the centrifuge will start to spin very quickly forcing the liquid metal into the flask.  When the metal is cold, the whole flask, containing the plaster and metal jewelry items is then quenched is a bucket of cold water to dissolve the investment and to harden the metal.  After the metal inside of the plaster has been allowed to cool, the plaster is then chipped away.  The original wax mould is gone, and the silver piece replaces it.


The piece is then cut off with a diamond cutoff wheel.  It is then ground smooth and rubber-wheeled.  The piece is then buffed and cleaned. Antiquing is added to darken the design and then the piece is re-polished and cleaned.

 

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