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Ceramic Mold and Bronze Pour The wax figure is molded. From "Trade School" episode DTRS-310

In this segment, apprentice Jeff Herndon continues his education in the many aspects of foundry work.

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Figure A

Now in another portion of the foundry, Jeff encases the wax segments by layering on a heat-resistant ceramic shell mold. After the wax melts away, it's this shell that will eventually hold the molten bronze.

1. Grasping an attached metal handle, Jeff dips a segment of the piece into a vat of yellow ceramic slurry (figure A). He dabs slurry into the smaller crevices with a paintbrush.

2. Then he coats the slurry with liberal amounts of very fine sand to pick up each piece's details (figure B), and then hangs the segment on a rack to dry. For the subsequent coatings--which build up the shell after Jeff dips the segments in the slurry--he instead places them in a bin full of air-fluidized sand (figure C).

3. After several more coatings to build up the shell, Jeff wraps each piece with metal wire (figure D). The wire acts as rebar and serves to bolster the thickness of the ceramic shell. Jeff continues adding layer after layer of ceramic materials until each shell achieves the proper thickness.

Figure B

Figure C

Figure D

4. With the wax segments now encased in a thick ceramic mold, Jeff takes them to the pour floor section of the foundry. Here, all of his earlier preparations come to fruition as he fires the ceramic in a powerful kiln, which also melts out the wax. He's now finally ready for the bronzing process.

Safety Note: Molten metal is extremely dangerous and should always be used by professionals. Always wear heat-resistant clothing and mask when working around molten metal.

5. Jeff begins this process by positioning each segment onto the kiln platform (figure E). Under each piece, he places a slotted steel disc, which allows the wax to drain out through a tube and collect outside the kiln for reuse (figure F).

6. At the push of the button, the pieces slide into the kiln and fire for 20 minutes at 1600 degrees (figure G). Afterwards, Jeff removes the now wax-less ceramic shells and sets them in front of several fans to cool and set.

Figure E

Figure F

Figure G

7. While the ceramic shells cool, Jeff places several bronze ingots into an induction furnace (figure H). The furnace melts the bronze to a white-hot temperature of around 2,000 degrees. Jeff agitates the bronze using a steel rod, which causes impurities called slag, to rise to the top (figure I). He skims off the slag using a steel paddle (figure J).

Figure H

Figure I

Figure J

8. When the bronze completely melts, Jeff returns the ceramic shells to the kiln to heat them up. Once hot enough, he places them, cup and sprue bars-up, into a bin lined with sand, which stabilizes the shells. With the shells ready, Jeff tips over the furnace to carefully fill a ceramic crucible with the molten bronze (figure K).

9. Working quickly and deliberately, Jeff uses a pulley hoist to maneuver the crucible, and then pour the liquid bronze into the shells (figure L). The molten bronze flows into the cup, distributes into the sprue bar channels and coats the insides of the shell. When the pouring is done, he transports the bronze-filled molds back to the cooling area using a metal hook.

Figure K

Figure L

In the next segment, Jeff breaks off the ceramic shell and proceeds with the metal phase of his education.