We finished the mold for the first figure grouping this week and hope to finish the second figure in this coming week. Please check out Meg's blog, as she went to Reed Quarry in Bloomington, IN on Friday and bought 2 huge blocks of stone (I'm going to try to talk her out of the smaller one). The 16 ton block is for a commission in Charles City, Iowa.
Sunday, May 10, 2009
If you're overbooked with sculpture commissions and you need molds real fast, who you gonna call... Meg had approval on her clay-for-bronze sculptures for the Emily Cooper Memorial. It was time to put molds on the pieces and ship them to the foundry. The first step was to dismantle the first figure group into manageable pieces. We are removing the dove from the babies hands. In certain instances, it is best to cut off appendages to make the molding process simpler. We have removed the babies arms and legs. Next, we will slice through the woman's wrist and remove her arms. The small pieces are pinned to boards, so that we can make 2-part molds on each piece. We were able to enlist the help of Steve McMillen. He and I did all the mold work, so that Meg could move on to other projects. Steve is applying vaseline to the boards so that plaster and rubber won't stick to them. Steve is spraying a mold release onto the clay before applying the rubber mold compound. We use the 2300 from Polytek. The next step was to apply 2 coats of rubber. We use polygel 40 from Polytek. You mix 2 equal parts and apply with a brush. It's important that you apply the first coat very carefully, because that will pick up the details of the clay work. I draw the part lines on top of the second coat (when it is firm) to help determine where to put the shims. Next, we cut plastic shims to make the part lines. We use bubble sheet from Sculpture Depot in Loveland, Colorado. We mix a regular batch of Polygel 40 and then add Polyfiber (from Polytek) until it is knife-grade (not runny) in thickness. We put the thickened mixture into a ziplock bag, cut a corner and apply it like someone would apply icing to a cake. By squeezing a finger-sized line onto the part lines, we can stick the plastic shims into it and it will hold. We tape the pieces of plastic bubble shim together. We heard something on the windowsill, eating the bird seed during a heavy rain. After making and attaching the shims (the hardest part of the job), it's a simple matter of applying successive coats of rubber until you get the desired thickness (1/4 to 3/8 of an inch). On the last coat, you want to make sure that there are no undercuts, so that the plaster mother mold will release. Iron Maiden? The bubble shims have a cool look. Baby Hans Solo in Carbonite? The last step (not counting de-molding) is applying the plaster mother mold. We use Tuff Cal which is a hydrocal with fiberglas fibers. It is formulated to be extra tough and strong. The mother mold insures that the rubber mold will retain it's shape when wax is poured into it. We apply a coat of plaster about 3/8 of an inch to the rubber. Then we spread a layer of hemp fibers which gets covered up by another 3/8" of plaster. The embedded hemp fibers add lots or resilience and strength to the mold. (Hemp? the jokes just write themselves, don't they).