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Lost Wax Bronze Casting Processes 7 - 9
7) A completely "sprued" wax copy is then dipped into a ceramic slurry, and this wet object is further dipped into a mixture of powdered clay and sand. This is allowed to dry, and the process is repeated until a half-inch thick or thicker surface covers the entire piece. Only the inside of the cup is not coated. The flat top of the cup serves, coincidentally, as the base upon which the piece stands during this process.
8) Once several of these ceramic-coated sprued wax copies are dry, they are placed cup-down in a
kiln and the wax inside them melts out. This is why the method is known as the Lost Wax process! Kiln-heating serves the dual purpose of hardening the ceramic coatings into a hard shell. Often, the melted "reclaimed" wax is collected and reused again and again. Now all that remains of the original artwork is the negative space, formerly occupied by the wax, inside the hardened ceramic shell. The feeder and vent tubes and cup are now hollow, also.
9) The ceramic shells are allowed to cool and are tested to see if water will flow through the feeder and vent tubes in the way that was predicted when the wax copy was being "sprued." Holes are sometimes drilled into the shell to test the thickness, and are patched over with thick ceramic paste. Any cracks or leaks in the ceramic shells are also patched.