Lost Wax Casting Process
A good foundry is invaluable to any bronze sculptor. Their knowledge of the ins and outs of the process can often make or break a design. I am privileged to have wonderful working relationships with two foundries. Kalispell art casting in Kalispell Montana and Bronze art Casting in Calgary Alberta.. Both offer exceptional quality in the end product and both are willing to work with me personally to see that what I have envisioned for my work is what actually shows in the final sculpture. I never underestimate the importance of these people in my ability to do my works.
I thank them from the bottom of my heart.
The lost wax process is the oldest casting method for most metals, including of course bronze. First developed during the bronze age this casting method is more efficient than the traditional, and less expensive sand casting process. The lost wax method preserves more of the tradition involved with the artistic making of fine arts crafted from metal, thus giving more importance to the intricate detail of the pieces. This process is composed of several steps, which are very briefly explained here.
Making The Mold
The original sculpture should be made of a material suck as clay, plaster, stone, or wood. The mold maker examines the sculpture and decides how to divide the master. The number of divisions depends on the complexity of the design.
The mold most often used involves applying rubber onto the original, building to a ¼ " thickness. Then covering the flexible mold with a rigid material called a mother mold made of plaster or fiberglass.
Once the mold is prepared, the original sculpture is removed and a hollow wax replica is poured.
Preparing the wax
The wax original is prepared following de-molding by chasing seam lines, touching up the surface and checking detail. Since the wax will serve as the pattern for the finished bronze it is important to check it carefully before moving on to the next step. At this point the casting is etched with an edition number. Having an edition allows the artist to spread the mold costs over the whole series.
Then the gating system is fitted, which is the system of channels through which the molten metal flows. Constructed correctly the gating system ensures a quick, smooth flow of the molten metal. This structure is also necessary to allow gasses and air to escape. Attaching sprees to the wax with a hot metal tool and attaching a wax-pouring funnel make the gating system.
The prepared wax, complete with the pouring gate and cup, is evenly coated with a slurry made of colloidal silica and silica flour, then left to dry and harden in a controlled atmosphere.
The first layer picks up all the detail. Subsequent layers of ceramic shell are then applied, including large particles of fused silica, which eventually build up to a stucco like appearance. Each application must be allowed to dry and harden before another coat is applied.
When the desired wall thickness has been achieved, the entire piece can be prepared for de-waxing.
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.
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.
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.
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 esthetic 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.
To view more of Diane M. Anderson's incredible sculptures, please go to her website.
You can also contact Diane directly through email
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Diane M. Anderson Tymarc Studio
P.O. Box 44
Canada, T0M 0R0
Phone: (403) 637-2274 Fax: (403) 637-2274
E-mail: firstname.lastname@example.org Website: www.dianeandersontymarc.com
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