Saturday, November 27, 2010
Ball Mold For Shoulder Joint
Today I made a ball mold for the shoulder joints of the new upper torso. This is a photo of the second half of the mold being prepared for pouring. The mold has been sealed with clay. Registration keys have been carved into the first plaster half of the mold with a spoon. The mold has been soaped.
I will mix the same 2:3 ratio of water to plaster as I did for the first half of the mold. For this small mold I'm using one half pound of water to three quarters pound of plaster. The plaster has been sifted into a bowl. The water has been weighed. I will put a bowl on the scale, and adjust the scale to zero. Then I will add the water. The scale will read one half pound. Then I will add plaster evenly to the bowl of water until the scale reads one and one quarter pounds. I will let the plaster sit without disturbing it until all the plaster has absorbed water. This is called slacking. Then I will stir the plaster for about a minute with my fingers, making sure all lumps have been mashed. I will turn on the vibrator, then pour the plaster into the mold. I already know that there will be some extra plaster left over. I have a bucket of water ready to clean out the plaster mixing bowl. Then I will let the plaster sit for one hour to set up. Finally, I will split the mold open, and clean it up. It will be ready to cast carving wax balls into.
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