The Process of Casting Metal
I like to create my projects first out of plasteline clay, water based clay or carve them out of wax. Then I make a latex mold around it so that it can be cast again in wax using the lost wax process for casting metal. I like to have this mold just in case I don’t like the way it casts the first time, then I can redo it until I am satisfied. I find flexible latex molds the best approach for my casting work. The image on the left is covered in latex mold material, the next two pieces were carved in wax, and the last image on the right is a piece cast in bronze. The blocks of wax behind the last image is the type of wax you use for the lost wax process.
Before I cast the latex mold around the sculpted project, I use many types of clay or dental tools to work the wax into the right textures and detail. This may take up to two weeks depending on the project and its difficulty.
Next I paint the flexible latex material all over the surface of the project until it has about a 1/4 thickness on all surfaces. Then, I allow it to dry. Next I make a backup mold, called a “mother mold” to support the latex once I pull the project out of the mold. Next I pour hot wax into the latex mold that is supported by the mother mold so that I can get a clean wax cast that will reproduce well in metal. After the wax is cooled, I remove the mother mold and peel the latex off the cooled wax.
The next step is where you add wax rods called “sprues or gating” to the project that are attached to a cup of wax. The metal is poured into the cup so that it can flow into the channels of sprues and allow the metal to fill into the cavity of your project.
Once your sprues are set, you turn your project so that the cup is facing down and so that the wax can be melted out via the channels of sprues you attached. Next you build a frame called a “cottle” with chicken wire and tar paper. This is wrapped around the piece so that it has about 1” - 1 1/2” of open area on all sides of the piece. Once your cottle is ready then you mix up a mold material that is meant to be baked in a kiln and allows the wax to melt out leaving a cavity of an inverted shape of your project. This mold material is referred to as investment. It depends on the artist what type of formula they use, but the concept is mostly a plaster and sand based mixture. Next you remove the tar paper, and you load it into the kiln so that the mold is firmed up and the wax is melted out.
After the wax has melted out, you remove the mold from the kiln. Then you vacuum out any debree that might have slipped into it. Next you cover the holes where you pour the metal with paper. The paper keeps the mold clean of debree until they are successfully buried in sand. The molds are packed into a sand pit to prepare for the pouring of the metal and to keep the molds intact while pouring metal. Crucibles are then loaded with metal ingots that will melt and be poured into the molds. The metal can be thousands of degrees hot, depending on which metal you cast. The temperature is continually checked to make sure its the right one for the metal you use.
When the metal is the correct temperature, it is removed from the metal kiln via a crucible. It’s carried to the sand pit full of molds using a crane and clamp system. The metal is then poured into the cavity left by the melted wax and allowed to cool for a couple of days.
When the metal has cooled, the sculpture is removed from the baked investment mold. The investment is air blasted, chiseled, or wire brushed off of the metal and the gating|sprues and cup are cut off. I like to scrub, polish, and then color the metal with a patina. I seal the sculpture with a metal sealant to keeps its luster. Lastly, I mount the sculpture so that its presentation ready. This piece is a “FUNK”tional piece using a pinecone as a back scratcher cast in aluminum.
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Check out the cartoon verion of how to cast metal!