Casting Bronze,Casting Bronze

Lost Wax Casting in Bronze

 
Sculpting
Each sculpture begins as an artist’s inspiration. Concept, size, details, where and how the piece will be displayed, are all important factors to determine before beginning the sculpting process. The sculpture's genesis starts with armature. When sculpting in clay, the armature serves as the support system for the piece, much like the human skeleton. The armature is constructed in a very basic shape of the finished piece. Think "stick" men similar to a drawing a preschooler might make. Armature can be made of anything that will act as the support system for the clay. Smaller pieces might use wire in conjunction with household aluminum foil and the clay built up over the surface. Carved foam has become common for very large pieces.

Actual sculpting take place once the clay is applied over the armature. This is where the sculpture starts to come to life. Using a variety of sculpting tools, but including "makeshift" tools to achieve the desired effects, the details are added, right down to the stitching on a pocket . Once the clay sculpture is finished, the original is signed, dated, and the edition number carved into the clay. The clay sculpture is photographed and measured before heading to the mold maker.

Actual sculpting take place once the clay is applied over the armature. This is where the sculpture starts to come to life. Using a variety of sculpting tools, but including "makeshift" tools to achieve the desired effects, the details are added, right down to the stitching on a pocket . Once the clay sculpture is finished, the original is signed, dated, and the edition number carved into the clay. The clay sculpture is photographed and measured before heading to the mold maker.

Making the Mold
The first step in the casting process is making the mold. Although the sculpture is carved in a solid piece, it is then strategically cut into smaller pieces for the casting process. The mold maker determines the best places to dissect the sculpture based on, among other things, the pouring of the molten bronze and welding joints. Each section is marked with notches for proper realignment when assembled.

Creating the rubber mold involves pouring liquid silicone over each section. Depending on the size and shape of each section, the mold may be made in hemispheres, meaning two sides are made, that will eventually fit together. The cured silicone mold is soft and pliable, and easily "peeled" off the clay sections. It is from this "mother mold" that all the finest details are captured and will translate into the final bronze. The next step in the process calls for the flexible rubber to be stabilized by the an application of plaster to the exterior of the rubber mold. The plaster exterior keeps the rubber mold from distorting and shifting during the next step of the process.

The Lost Wax Process
The next step defines the "lost wax process." Once the plaster is hardened, it's time for hot wax to be poured into the "mother mold". A thin layer of 200 degree wax is applied to the inner cavity of the rubber mold. Very thin layers are applied one after the other until they are built up to the desired thickness. The thickness of the wax layer will determine the thickness of the bronze sculpture in any given area. It is important that each successive layer is poured at a cooler temperature so that it does not melt the previous layer. When completely cooled, the wax shell is then pulled from the mold.

After being pulled from the mold, the positive-imaged wax sections are connected and hand finished, or "chased" to remove any imperfections and perfectly duplicate the original sculpture. The quality of the final sculpture depends on maintaining the integrity of the details at this stage.

The wax form is now prepared to accept the, molten bronze. This is accomplished by strategically attaching a series of hollow wax channels or branches. These channels create the "gating system" that will allow the molten bronze to flow into the cavities created when the wax is melted.

The finished "tree" is dipped into a ceramic slurry and coated with silica sand. This process is repeated 8-10 times, drying between each layer, until a hard shell is created. When fully dried, this ceramic shell is placed in a burnout oven heated to over 1,000 degrees. The internal wax melts, creating a hollow cavity. Hence the term "lost wax".

Casting the Bronze
While the shell is still hot, the bronze alloy is heated to over 2,000 degrees, and poured into it. It takes teamwork to successfully pour the bronze. The “lead pour” directs the crucible which holds the molten bronze. The “dead man” maintains the balance of the crucible. A third skims away the impurities or “slag” that collects on the surface of the bronze.

Once cooled, the ceramic mold is broken away from the bronze. The gating system which has also been cast in bronze at this point, is removed. The surfaces of the cast bronze are sandblasted, cleaning the crevices of any ceramic residue.

Using the notches as guides, the sections are pieced back together and welded. The bronze is "chased" or finished by filling any small pits that might have developed and filing down any excess surface metal. Weld lines are sanded down and any lost details restored. Finally, the sculpture is prepared for patina by sandblasting of the surface.

The Final Bronze
Patina, or the coloring of the bronze, is now applied. Patinas are created when heat is applied to metals salts, each having their own properties and resulting in finishes unique to these properties. Different application techniques, such as dabbing or spraying, yield different results. Patina artists often have their own signature recipes that become proprietary to their foundries.

Following the patina process, the bronze receives a wax sealant. A layer of hot carnauba wax is applied and hand rubbed onto the surface of the sculpture. An additional two or three more coats are applied and hand buffed to bring out a fine luster and shine. Once the sculpture is attached to a base, it is ready for delivery.

 

 

A Sense of Curiosity

Visit Caswell Sculpture in Historic Downtown Troutdale - Gateway to the Scenic Columbia River Gorge!

 

Cell: (503) 502-7756  

Ph: (503) 492-2473

Email: info@caswellsculpture.com  

Mail:  P.O. box 850 Troutdale OR. 97060  

Studio: 903 E. Historic Columbia River Hwy. Troutdale OR. 

Gallery:253 E. Historic Columbia River Hwy. Troutdale OR.

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