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Building a plaster mold

Here's a #deepdive into my process!! There are two major steps to my process. First is to make a plaster mold from a real object, which can be used many, many times. The second step is to create the clay objects from these molds. Here's a basic video of how I make the molds!


I choose the most perfect, and largest of whatever I want to mold. Largest, because the clay shrinks about 20% in the kiln, so I need to start off big if I want it to end up normal size. Some food objects have textures or moisture that will prevent the plaster from setting up properly, so I sometimes spend a lot of time figuring out how to get around that: carefully blotting off lemon juice from the cut section, creating a little clay bed for the oysters to be pinned down to, a water barrier over the avocado flesh because it does something weird to the plaster... Every object is a different challenge!


Then I have to divide up the shape of the 3D object so that the sections of the mold can pull straight away from the cast, releasing it without hooking onto an undercut. I build up clay around the object, up to the line that I established as a mold divide, to block off the future sections from the first plaster pour. This step is a fun brain activity for me, like deconstructing a three dimensional puzzle.


Then I clamp wooden "cottles" around the clay/object assembly, to create a container for me to pour plaster into. Such an under-appreciated step: I used to halfass this part and more than a few times I ended up with quarts and quarts of liquid plaster busting the dam and splattering allllll over the place. What a mess!


Next, I take off the cottles, flip the beast upside down, so that I can peel the clay away from the newly set plaster of the first mold piece. I shave down the plaster to the cleanest shape, add round "keys" so that the mold pieces all fit together exactly and firmly, and then paint Murphy's Oil Soap all over the exposed plaster. This works as a really great mold release, because plaster poured onto old plaster will just permanently bond together, and the oil left by the soap prevents this.


Now it's time to start on t