While lost wax casting has been around forever, every foundry has their own process and protocol. In a nutshell, the sprued waxes are dipped into a tank of colloidal silica binder which wets the surface. The wax is then dipped into a layer of zircon so fine that it can capture the finest detail. This process is repeated using varying solutions and grades of sand until the wax is completely covered in seven to ten heavy coats of the stuff.
Remember back when I said this would all make sense later? Well, once all of the layers of shell are dry (the whole process takes over a week), the entire piece is inverted and placed into the de-waxing oven which will reach temperatures exceeding 900 degrees. Here's why it's called lost wax casting: all of the wax from the sculpture turns to liquid and pours out through the sprues leaving a perfectly clean negative space inside which has hopefully captured all of the detail perfectly. When this process is complete, bronze can be poured inside and will fill all of the voids of the original wax model.
Here are some photos to better illustrate the shell process:
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| The first dip into the colloidal binder. |
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| My buddy Brad makes sure that every detail is captured. |
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| Letting the colloidal drain. |
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| The first dip into the zircon. |
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| Looking good! Great job, Brad! |
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| You can see the zircon pouring off like sand. |
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| Heavier silica is eventually applied, replacing the ultra fine zircon. |
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| The base gets the same treatment. In the background you can see the other pieces going through the process as well. |
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| Attention to every detail is very crucial. |
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| The eighth and final coat. |
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| Now it's time for everything to dry before the de-waxing process can begin. |
I hope this has illustrated the basics of the shell process. After a few days of drying (aided by forced air blown through tubes into the shells), the shells will be de-waxed and the pouring of the bronze can begin. Stay tuned!
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