I recently made a bunch of new molds, while on a long visit up to Cincinnati to visit my mom. I turned part of the basement at her house into a little mold-making workshop - clearing up years of clutter and then stinking it up with old seafood. Here's a little about my process:
It's important to me that I take molds of REAL things, so that I can capture the realistic textures and proportions and beautiful little spontaneous details. So I got some live blue crabs from a seafood market in Westwego, on the West Bank of New Orleans - live because that's the only way I could get the claws 😣
To make the mold, I essentially have to block off half the claws from the first plaster pour, then remove the clay used to block off, exposing the other half of the claws, and then pour a second side of plaster - encasing the claws in two separate chunks of plaster.
To create the blocked off half, I use plasticine clay, which is pretty firm, but becomes quite soft and easy to manipulate when warmed in the microwave. The tricky part is being really smart about the perimeter line at which the two plaster blocks divide the claw, as this line is really sensitive to any undercut in the three-dimensional shape. If I overshoot this line, the plaster will break off and I'll have a flaw in my cast that I have to repair every time. Also, the crispness of this line, and the smooth texture of the blocked off surface, is important to the result of a clean, long-lasting, accurate mold. Plasticine clay is the best method I've found for achieving this!
Once half the claws are blocked off by carefully applied plasticine clay, I pour liquid plaster (Pottery Plaster #1, not plaster of paris) around the exposed claws, and wait for at least an hour for the plaster to set. I peel off the plasticine clay from the claws half buried in plaster in one piece - another reason I love the plasticine as opposed to regular clay. Then I have to treat the plaster with a release agent before pouring the second plaster piece, otherwise they'll stick together! The best thing that I have found for this, by far, is (oddly) Murphy's Oil Soap, which is a wood floor cleaner that puts down a thin, waterproof layer of wax, that will later flake off leaving the plaster uncoated. It's perfect for the job, don't waste your time with other mold release agents :) After waterproofing the first plaster piece, I pour the second chunk of plaster around the other half of the claws, and wait a few hours for the plaster to begin to cure. Plaster is a complicated, amazing material, and I'm happy to nerd out on that in a future blog post.
Here's the process shown more completely, and the resulting amazing first casts, from an instagram post.
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