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offcntrBack when I worked for Slippery Bank Pottery, I spent a winter (when I'd caught up with all of the hummingbird feeders, spoon rests et al) recasting all of Will's plaster slip-casting molds. He probably had a couple dozen, mostly one-piece, open-topped baking dishes, though he did have me make a two-piece lamp base. Some of his forms were original models, though I was surprised to find that many were commercial bakers with the logo ground off. I went through a good 200 lbs. of #1 Pottery Plaster that winter, and got very good at mold prep, mixing, pouring and clean-up. (Secret to clean-up when a mold form splits and plaster pours out all over the floor: walk away. A pottery studio has a thin layer of dust on everything, and after the plaster sets, you can pop it up in sheets with a drywall blade.)
I used the skills to good effect when I offered a Tile Making class, where we each molded a sculptural relief tile, then cast a mold to make multiples, but I don't really do much plaster work in my own business. Except for this one thing…
City mugs. Specifically, the City of Eugene commemorative employee five-year appreciation mug. It's got a sprigged city logo on one side, employee's name painted on the other. I've been using the same plaster mold since I started doing them, lo these many years ago. And they just informed me that the design has changed.
So Monday, while the glaze kiln was tootling along towards cone 8, I sat down with my tools, clay, and the new logo, and made a new one.
I worked with thin layers of clay on a glass sheet--a scrap of mirror I had in the studio. I sized the logo on my computer and printed out several copies. (Because the old one always looked a little weird from the curvature of the mug, I expanded this one 10% horizontally. With a little cylindrical distortion, it should end up looking round.) Traced the pattern lightly with a needle tool, then cut, peeled and modeled the layers with an X-acto knife and sculpting tools.
After the master was finished, I made a cottle with thick clay slab, estimated the volume (easy with a cylinder) and mixed up a batch of 73 consistency (73 parts water to 100 plaster, by weight) plaster. When it was the consistency of heavy cream, I poured it into the mold, being careful not to splash onto the form. Slowly filling in from the side keeps from trapping air bubbles in the letters or the little building silhouettes. Extra plaster is dumped into a bowl lined with newspaper and allowed to set before trashing, and the mixing bucket is thoroughly washed.
After that, it's a matter of going away for half an hour or more, until the plaster has set and absorbed any surface water. At that point, I pulled off the cottle, peeled out the seal, and touched up any fins of plaster that had seeped between layers of clay.
The mold is now drying in the warm kiln room. In about a week, I'll start making City Mugs 2.0 for all those appreciated 2010 hires.
I used the skills to good effect when I offered a Tile Making class, where we each molded a sculptural relief tile, then cast a mold to make multiples, but I don't really do much plaster work in my own business. Except for this one thing…
City mugs. Specifically, the City of Eugene commemorative employee five-year appreciation mug. It's got a sprigged city logo on one side, employee's name painted on the other. I've been using the same plaster mold since I started doing them, lo these many years ago. And they just informed me that the design has changed.
So Monday, while the glaze kiln was tootling along towards cone 8, I sat down with my tools, clay, and the new logo, and made a new one.
I worked with thin layers of clay on a glass sheet--a scrap of mirror I had in the studio. I sized the logo on my computer and printed out several copies. (Because the old one always looked a little weird from the curvature of the mug, I expanded this one 10% horizontally. With a little cylindrical distortion, it should end up looking round.) Traced the pattern lightly with a needle tool, then cut, peeled and modeled the layers with an X-acto knife and sculpting tools.
After the master was finished, I made a cottle with thick clay slab, estimated the volume (easy with a cylinder) and mixed up a batch of 73 consistency (73 parts water to 100 plaster, by weight) plaster. When it was the consistency of heavy cream, I poured it into the mold, being careful not to splash onto the form. Slowly filling in from the side keeps from trapping air bubbles in the letters or the little building silhouettes. Extra plaster is dumped into a bowl lined with newspaper and allowed to set before trashing, and the mixing bucket is thoroughly washed.
After that, it's a matter of going away for half an hour or more, until the plaster has set and absorbed any surface water. At that point, I pulled off the cottle, peeled out the seal, and touched up any fins of plaster that had seeped between layers of clay.
The mold is now drying in the warm kiln room. In about a week, I'll start making City Mugs 2.0 for all those appreciated 2010 hires.