Today I made a mold for a special order platter. I could just make one without the mold, but this size is the good medium size oval platter between my 15″ and 22″ oval platters.
First I made a model (platter) with a slab of clay and shaped its wall placing a coil of clay underneath according to the paper template I made. Then, weigh the water and the plaster (#1 potter’s plaster) at 70:100 ratio. Always pour the plaster into the water, then stir for 5 minutes. I poured the plaster mix into the model, and placed a wood block on its top. Wood block has two nails (screws) to anchor into the plaster. This wood block gives the mold the height, so I can easily trim excess clay from underneath. Waited for 20 minutes, and flipped over and removed the master. Then shaped the edges with the surform shaver. Let it dry for a couple days before using it.