ronfire Posted August 31, 2023 Report Share Posted August 31, 2023 I have a plastic platter that I try to make slab patter with M340 clay. I have a problem with the rim always cracking. I use Pam as a release agent and still have issues. If I make a plaster mold will this solve the Cracking issue with a more even drying? What plaster would you recommend? I would have to first make a mould of the platter ( Hump mold )and then build the slump mold so I do not get the shrinkage problem with the clay. Quote Link to comment Share on other sites More sharing options...
Jeff Longtin Posted September 1, 2023 Report Share Posted September 1, 2023 Welcome to the Forum Ronfire. Do you have a picture of the plastic form? Do I understand correctly that you slump clay OVER the plastic form and its cracks? While Pam is one solution you could, as well, try covering the plastic form with cloth, so that the clay shrinks against cloth surface rather than the plastic surface itself. (Take the Pam aspect out of the equation.) Plaster - if the form meets the tabletop at a sharp angle you may still have cracking issues. (Even if you make it in plaster.) Are you making platter forms with feet? This adds complexity to the slump mold process. Quote Link to comment Share on other sites More sharing options...
Min Posted September 1, 2023 Report Share Posted September 1, 2023 On 8/31/2023 at 8:34 AM, ronfire said: What plaster would you recommend? #1Pottery Plaster. Quote Link to comment Share on other sites More sharing options...
Tamra Posted September 1, 2023 Report Share Posted September 1, 2023 Well at least I got the #1 Pottery plaster correct... Following... Tamra Quote Link to comment Share on other sites More sharing options...
ronfire Posted September 10, 2023 Author Report Share Posted September 10, 2023 I am just forming a slab rolled from M340 and placing it inside a plastic tray/platter coated in Pam. As the clay starts to dry the cracks form on the rim, even if I cover the clay with plastic I still get cracks. The clay is still moist enough that I can remove it and wedge it. Just made a couple of slump molds with #1 Pottery Plaster and will try with this in a few day to see if it will dry more even. Pres 1 Quote Link to comment Share on other sites More sharing options...
Roberta12 Posted September 12, 2023 Report Share Posted September 12, 2023 It could be the shape of the mold or it could be the thickness or thinness of the clay. I agree with @Jeff Longtin about the Pam. Try cloth as he suggested or cornstarch. Jeff Longtin 1 Quote Link to comment Share on other sites More sharing options...
Jeff Longtin Posted September 12, 2023 Report Share Posted September 12, 2023 I missed the question about plaster the first time I read the question. Like Min suggests a "pottery plaster" is your best bet. #1 Pottery is United States Gypsum (USG) pottery plaster. Georgia Pacific (GP) also makes a pottery plaster, K60. They're the same thing so either works for your application. (For many years #1 was only available in 100lbs. bags so I switched, to K60, when my back told me to do so.) Seeing that you are posting from CA I went to the Plainsmen website and looked up M340. It looks like they made some changes to the clay body, recently, so that MAY explain some of your problems. Plasticity can sometimes be a fickle thing so testing different making methods is really your only solution. The website comment, "You should have few problems drying smaller pieces but care and attention are necessary when making larger pieces" kind of jumps out at me. If it seems like an endless process perhaps another clay body might be worth trying? Good luck Pres and Roberta12 2 Quote Link to comment Share on other sites More sharing options...
ronfire Posted October 17, 2023 Author Report Share Posted October 17, 2023 Finally got the mold slump mold made and a platter from it finished. It worked well and I can finally get to make more of these platters. Pres, Callie Beller Diesel, Chilly and 2 others 5 Quote Link to comment Share on other sites More sharing options...
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