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Casting Process (page 2)

(page 2 of 2)

Burnout
Curing the ceramic shell and removing the wax is the next step in the process. The prepared ceramic shell is placed in a kiln pre-heated to about 1400 degrees(f). The wax is melted from its outer surface inward to prevent the expansion of the wax and cracking of the shell.

The melted wax is collected in a chamber below the kiln and may be used again. Once the mold is completely free of wax the shell is heated to over 1500 degrees and held at that temperature to burn off any wax residue.

Pouring the Bronze
Bronze is an alloy formed by blending copper and tin and sometimes combined with small amounts of Zinc, lead or nickel. Silicon bronze is commonly used in art casting and is an alloy of 95% copper 3% silicon and 2%zinc. The melting point is approximately 1850 degrees(f).

Bronze ingots are placed carefully into the crucible, which is placed into the furnace. Once the metal is at the correct temperature, the crucible is lifted from the furnace using special tongs and placed into the pouring shank.

The slag and impurities, which have floated to the surface, are skimmed off with an iron tool before the molten metal is poured.

The preheated metal is then poured quickly and steadily. Once the pouring is complete the casting is allowed to cool.

Breaking the Shell
Once the casting has cooled, the ceramic shell is broken off. This is done using a hammer to reveal the metal casting complete with pour cup and gates. Remaining shell chips are removed by sandblasting the piece.

Metal tooling
The gating system must be removed and the points of attachment to the sculpture must be chased clean. Separately cast parts are welded together using bronze welding rod, and the surfaces are ground to match toe original. Casting imperfections may be repaired at this time.

Patina
The final finish, is the patina, or application of color and texture. A wide variety of chemicals can be used to create various effects. Often heat is applied to the sculpture with a propane torch while simultaneously applying chemicals such as ferric, cobalt and silver nitrate through a sprayer or with a paintbrush.

Once the patina is complete, past wax is applied to the hot sculpture with a brush. When cooled it is buffed to s soft shine.

Mounting
Most artists prefer to mount the finished bronze on a wood base. Usually a hard wood such as walnut is used. Though the style varies greatly from artist to artist the purpose of the base is aesthetic as well as functional. Protecting furniture from the metal as well as giving the piece a finished look, a beautiful piece of wood can warm up the work itself.

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Diane Anderson Tymarc Art Studio P.O. Box 44 Cremona, Alberta Canada
phone or fax: 1-403-637-2274 email: tymarcartstudio@gmail.com

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