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oola

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    Pasadena, Los Angeles

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  1. No, the bowl curves outward at the top. It's a handmade bowl, so there might be a slight undercut, but I think the foot is mostly straight. This is my 2nd attempt at making a mold, and the first time I used a bowl that definitely should have worked (progressively wider towards the top, just a flat bottom with no inward foot) but experienced the same issue. I used pottery plaster #1 with the correct 7/10 ratio. Just to clarify, the plaster is definitely hardening, it just doesn't feel like there's much of a difference between an hour after I first poured and 2-3 days.
  2. Hello, I followed https://www.instructables.com/Plaster-Mold-for-Slipcasting-a-Bowl/ this tutorial to make my own 1 piece plaster mold. I used a similar bowl (ceramic bowl glazed on the outside) and followed all the steps (except for the slip reservoir part) and used Murhpy's Oil Soap as my release agent and rubbed it onto both the sides of the bucket and the bowl. I was able to rather easily release the actual mold from the bucket after it set for around 45 minutes by flipping the bucket and tapping the bottom. However, I can't seem to get the bowl out at all. I tried getting the bowl to shrink a little by pouring ice water into it, but that didn't work, and I spilled some onto the still hot and very moist plaster. I'm not sure if spilling did anything, but the mold has been setting for 2 days now, and it's barely hardening at all. I also drilled a small hole into the bottom of the plaster mold (don't want to damage the bowl) and applied air pressure, but to no avail. I've now read a little and learned that it's best to wait until the plaster sets fully as it will expand (and increase the gap between itself and the bowl), but I'm at a loss at what I can still do. If necessary I can break the mold and repour it, but it would be great to have some tips on how to prevent the same thing next time.
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