Following the trauma of the "wilted gates" incident described in my last posting, the invested pieces were loaded into the kiln and a successful burnout was achieved. Next came the manual labor phase of the process. The molds were set up in wooden flasks and then the flasks were packed with dampened sand. The pour itself went very smoothly and all that remained was to wait until the molds were cool enough to handle.
The first step in the break-out process involves taking a hatchet and cutting a shallow gouge down the length of the side of the mold. It needs to be deep enough to cut through the chicken wire surrounding the gated work, but not so deep that you run the risk of damaging the bronze castings. Next you use a wooden wedge and a hammer to try to pry the halves apart. If the casting is fairly simple in shape, this can be done relatively easily. If the casting is more complex it can take quite a bit of careful chiseling away of the investment materials (still using a wooden wedge, because a metal tool could damage the surface of the casting). Another helpful technique to remove stubborn investment from the casting and gates is to pound the sprue cup with a heavy hammer. The vibrations act to separate the material that is still clinging to the remaining nooks and crannies.
After eliminating the majority of the investment, I cut off most of the vents, gates and sprue cups so the castings could be individually bead blasted to remove the remaining thin coating of investment material. This made it easier to cut off the small sections of gating that were still attached to the more delicate and hard to access areas of the castings. The next step will be to grind down the attachment points, remove any surface imperfections and then re-texture those areas to match the surrounding surrounding surfaces. Stay tuned....
...cast bronzes after preliminary bead blasting with most of gating removed
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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.