Now is the time to add the sprues to each piece. A sprue is a downward channel the bronze will follow into the mold. The mold should fill quickly, so that the metal doesn’t cool before the mold fills, and completely, so there is no area in which air is trapped, causing a void in the finished piece. This is a matter is visualizing the flow of metal through the piece as you turn it to discover the optimum position which will accomplish both. Of course, there is some intuition and experience involved too, and every piece must be considered uniquely. In some cases there are vents which give a path for air to leave the mold from areas where it might otherwise be trapped. I naturally tend to overdo this sort of thing, but since these pieces have some thin and narrow sections, I want to be sure that the metal will not “freeze-out” or cool anywhere, so I have placed a sprue into each hand foot and head to get metal into every area. As well, all those sprues can serve as vents too.
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