pinchedbysalas Posted May 5, 2023 Report Share Posted May 5, 2023 I am trying to make at least 30 little cups/copitas (small enough to fit a little over 2 ounces of liquid) and made plaster molds so they’d be more similar. I put the colored clay on the hump molds this morning and I still can’t seem to get them off. I left them outside for over 4 hours and they’re dryer to the touch, but still not dry enough to be able to slip the cup out! Anything I can do to speed up the process? I tried the hair dryer.. Quote Link to comment Share on other sites More sharing options...
Roberta12 Posted May 5, 2023 Report Share Posted May 5, 2023 Could you send a picture? You said hump mold but then said you couldn't get the cup out. Does that mean you put the clay inside a mold or outside on the mold. Usually my plaster molds dry clay very quickly. But I live in a dry area. Were your plaster molds cured? I usually wait a few days before using them. Just throwing out some ideas. Roberta Min and Rae Reich 2 Quote Link to comment Share on other sites More sharing options...
Callie Beller Diesel Posted May 6, 2023 Report Share Posted May 6, 2023 If you’ve used a hump mould, you have to unmould them sooner than you would a slump or casting mould. Clay shrinks as it dries, so it sounds like your pieces are stuck. You might have needed to remove them at 2 or 3 hours to get them to release easily. Rae Reich 1 Quote Link to comment Share on other sites More sharing options...
Min Posted May 6, 2023 Report Share Posted May 6, 2023 If you have a compressor a puff of air between the plaster and the clay works really well to help with release. Rae Reich 1 Quote Link to comment Share on other sites More sharing options...
CarolineL Posted January 16 Report Share Posted January 16 Hello, I have a similar problem. I built a wood mold or frame and have the clay on top of it and it’s cracking even though keeping it wet. Is there something that can be put between the wooden mold and the clay like bubble wrap so it addresses the shrinkage problem? Quote Link to comment Share on other sites More sharing options...
Min Posted January 16 Report Share Posted January 16 3 hours ago, CarolineL said: Hello, I have a similar problem. I built a wood mold or frame and have the clay on top of it and it’s cracking even though keeping it wet. Is there something that can be put between the wooden mold and the clay like bubble wrap so it addresses the shrinkage problem? Just to confirm I'm reading this right, the clay is cracking as it's shrinking on the wood mold/frame? You are keeping the clay wet? Quote Link to comment Share on other sites More sharing options...
CarolineL Posted January 17 Report Share Posted January 17 Here is a picture of the clay on my wooden mold, and it keeps cracking, even though I’m keeping it wet with a wet sheet and plastic over that to dry it slowly. 2 hours ago, Min said: Just to confirm I'm reading this right, the clay is cracking as it's shrinking on the wood mold/frame? You are keeping the clay wet? thank you Min and yes, it is shrinking on the wood. And yes we were keeping the clay wet. Just severe cracks even in day two, not even trying to dry it out yet . Today I bought a piece of quarter inch open cell foam sheet that I will wrap around between the wood and Clay. Maybe that will absorb some of the shrinkage? is there something I should put between the wood and the clay that would address the shrinkage? Quote Link to comment Share on other sites More sharing options...
neilestrick Posted January 17 Report Share Posted January 17 Clay shrinks as it dries, especially from wet to leather hard. You have to get it off the form before it sets up too much. The wood will pull moisture from the clay and dry it out. Quote Link to comment Share on other sites More sharing options...
PeterH Posted January 17 Report Share Posted January 17 8 hours ago, neilestrick said: Clay shrinks as it dries, especially from wet to leather hard. You have to get it off the form before it sets up too much. The wood will pull moisture from the clay and dry it out. I find a picture often helps. Quote Link to comment Share on other sites More sharing options...
PeterH Posted January 17 Report Share Posted January 17 (edited) A few examples from the net: How to Make a Clay Cylinder - Ceramics Handbuilding for Beginners - YouTube Making a Clay Cylinder - YouTube ... and the three-part How I hand build clay cylinders. Part 1 Pottery ceramics techniques - YouTube How I handbuild clay cylinders Part 2. Removing the cylinder from the former. Handbuilt ceramics - YouTube How I handbuild clay cylinders. Part 3 Attaching the base - YouTube ... where the cylinder is worked on while on a former Note that a suitable diameter plastic pipe makes a good former being non-absorbent, smooth & strong. Edited January 17 by PeterH Min 1 Quote Link to comment Share on other sites More sharing options...
CarolineL Posted January 18 Report Share Posted January 18 Thank you, everyone! This is all so very helpful and I appreciate this forum so much. I will look at all of these links and learn!! Here is a picture of the clay on my wooden mold, and it keeps cracking, even though I’m keeping it wet with a wet sheet and plastic over that to dry it slowly. On 1/16/2024 at 1:12 PM, Min said: Just to confirm I'm reading this right, the clay is cracking as it's shrinking on the wood mold/frame? You are keeping the clay wet? thank you Min and yes, it is shrinking on the wood. And yes we were keeping the clay wet. Just severe cracks even in day two, not even trying to dry it out yet . Today I bought a piece of quarter inch open cell foam sheet that I will wrap around between the wood and Clay. Maybe that will absorb some of the shrinkage? is there something I should put between the wood and the clay that would address the shrinkage? Quote Link to comment Share on other sites More sharing options...
Bill Kielb Posted January 18 Report Share Posted January 18 (edited) 1 hour ago, CarolineL said: Here is a picture of the clay on my wooden mold, and it keeps cracking, even though I’m keeping it wet with a wet sheet and plastic over that to dry it slowly. It is really hard to keep it wet enough not to shrink a bit especially with shapes that cannot release somewhat. With a hump or inverted bowl shape the clay can shrink a bit and release up the mold. Your shape is sort of wider at the top than bottom so it will tend to trap the clay and not provide an easy way to remove. Any water that leaves the clay makes it shrink, ever so slightly. It’s really hard to rehydrate clay to its original amount just by spraying. For hump molds it’s good to have a plan for removal as soon as practical just to avoid this issue. I don’t think this is your fault, it’s just very hard to make this shape this way and hard to keep from shrinking just a little during construction. If this was made as a slump or inside this form you would not have these issues. Edited January 18 by Bill Kielb Quote Link to comment Share on other sites More sharing options...
CarolineL Posted January 18 Report Share Posted January 18 Thank you Bill. What might be worth trying is 1/4 foam around the wood, then a tight plastic then newspaper before draping the clay over this form. It’s time to experiment! Maybe like you said remake the form with the top being a bit smaller than the bottom so it can slide up and off. This is tricky business!! Quote Link to comment Share on other sites More sharing options...
JohnnyK Posted January 19 Report Share Posted January 19 Is the wood form straight or tapered? In the photo it looks like it is wider at the top than the bottom. How was the body of the wood fabricated and how is it attached to the base? WHat are the dimensions of the wood cylinder? Can you send a photo of the wood form without the clay? Quote Link to comment Share on other sites More sharing options...
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