JRWU Posted May 11, 2020 Report Share Posted May 11, 2020 Hello All, I am having a persistent difficulty when using a spherical plaster mold I made. I have only ever had this issue with two-piece spherical molds (one was 8 inches, and this one is ten inches in diameter). I pour the slip in, let it set for a thick wall (about an hour), then pour it out and let it dry in the mold (as usual). The problem is that, again and again, when I release the mold, I find that one half of the sphere has collapsed/separated from the plaster wall. At first I thought there was something wrong with how I mixed the plaster with my first mold, so I made another -- and the same thing happens. I read somewhere that this can be caused by a vacuum being created inside the chamber while pouring out the slip, such that a suction effect pulls the clay from the wall. Is there a way to avoid this? I try to pour out the slips gently and evenly to avoid the "glugging" that creates the suction, but it's pretty difficult to avoid it. There seems to be something especially difficult with this shape. Any ideas? Thanks! Link to comment Share on other sites More sharing options...
Chilly Posted May 12, 2020 Report Share Posted May 12, 2020 Get a syringe and syphon the slip out, then drain the last few drops. Link to comment Share on other sites More sharing options...
liambesaw Posted May 12, 2020 Report Share Posted May 12, 2020 Glug glug! You can make the well wider to make it easier to slowly pour. I've seen a fella put a bendy straw into the hole as well to act as a siphon break. I'm sure there's other ways to skin this cat, but I don't do a ton of slipcasting. Making the molds is so time consuming! I made a 3 piece over the weekend and it took me nearly all weekend to get it done. All that said, a sphere with one side sucked in a bit sounds kind of cool! Link to comment Share on other sites More sharing options...
Jeff Longtin Posted April 10, 2021 Report Share Posted April 10, 2021 As this is a problem many of my clients have complained about, over the years, I'll offer this suggestion: while a larger opening, in the mold, can help, the greater problem is the casting slip itself. Adding a little bit of water will reduce the amount of gelling that's occurring. It may require you to let the slip set longer, in the mold, but it will enable the slip to flow more easily. How many molds you're filling, each casting cycle, would determine how often you add water. I check my slip daily and often add water after each casting cycle. (Not much...but a little.) Link to comment Share on other sites More sharing options...
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