The wax maquettes that were encased in investment molds last week (see blog entry for 3/15/14) were loaded into the kiln and subjected to a burnout temperature of approximately 1,250 degrees for 30+ hours. This process removes all of the wax from the molds and dries out the investment. After the kiln cooled to a manageable temperature, the still warm molds were removed and lined up on a shallow bed of dampened sand. Long wooden flasks (frames) were placed around the molds and dampened sand was tamped in around them to within a couple of inches of the top of the molds. The sand serves to contain any spilled bronze and to insulate the molds. While we readied the molds, bronze ingots were melted in a crucible in the furnace at a temperature of about 2000 degrees. The crucible can hold over 200 pounds of melted bronze.
When we finished packing the wooden flasks with sand and the bronze was hot, the pour team suited up in their protective garments (face shields, leather jackets, and flame resistant chaps). The furnace was shut down and the hot crucible of bronze was removed using crucible tongs and an overhead hoist system. The crucible was then locked into a pouring shank attached to the hoist, moved along the overhead support beam, and lowered into position over the first of the molds. The hot bronze was poured into the mold until it was full and then the pour team moved down the line of molds and repeating the process. After the first 8 molds were poured the bronze had to be returned to the furnace for reheating to insure that the remaining molds would be effectively filled. (If the bronze is too cool it can solidify before the mold is completely filled.) A second pour teamed filled the remaining molds with the second crucible of bronze.
Once the bronze in the molds cools, the real work will begin. The gated bronze will have be broken out of the investment molds and any remaining investment will have to be cleaned off the surface of the bronze. Next the gating and fill cup will be cut away from the sculpture casts. The removal points will have to be chased and resurfaced, as will any areas with surface imperfections. This part of the process takes time and a lot of "elbow grease" Stay tuned!
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Cynthia Smith, Maine artist, originally from Connecticut. Taught art at secondary level for 35 years, retired in 2004. Sculpts in bronze, wood, stone, clay & plaster. Her work can be seen at several mid-coast Maine galleries and shows.