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The three traditional casting processes used for making multiple copies of three dimensional items are; sand casting, injection casting, and lost wax (or investment casting).   Sand casting, the least expensive process, is used for casting simple rough items where the surface finish is not critical, such as metal casings for street lights.  Injection casting is the most expensive process, mostly due to the very expensive injection molds needed for the process.  Injection molds are used for tight detail and high production – in the thousands.  The lost wax, or investment casting process, is what I will be discussing in the following blogs.  It is the preferred process for most limited edition art work and while expensive, it is not cost prohibitive and still able to maintain the detail required for quality, limited edition bronzes.  

A basic rule about the “Lost wax” or “Investment Casting” foundry process is that; in order to make editions of a sculpture, an “investment” is required.  To put it another way, for every casting made, a wax proof (or investment) must also be made first.  Below, I have listed the basic steps required for this process and I will attempt to explain each of these steps in subsequent blogs.

Basic steps

1. Make mold(s) and supporting shell around the mold. Remove the clay sculpture.
2. Pour hot wax into the mold and pull the wax proof out of the mold.
3. Clean the wax, sprue the wax, add to a tree and make shell/slurry mold.
4. Place the shell/slurry mold in an oven and burn the wax out.
5. Pour molten bronze into the shell/slurry mold, when cooled, break the shell/slurry mold off the casting.
6. Clean, repair and reassemble all parts of the sculpture to the casting.
7. Apply patina

The Original Sculpture

The original sculpture can be in any three-dimentional medium.  I, like most sculptors, work in Plasticine clay which is an oil and parifin based clay.  Plasticine clay has great modeling qualities and is very user friendly in that it never dries out, unlike water based clays.

To begin with, all lost wax, or investment casting, sculptures require a mold.  The reason, as stated earlier, that in order to get a metal casting, the process requires a “wax proof” (or copy) of the original sculpture.   

(continued to The Molding Process blog)