Danielle Caron Posted May 9, 2023 Report Share Posted May 9, 2023 Hi everybody, I am about to make my first plaster mold with a ceramic piece. I intend to use a thin coat of Murphy's soap onto the piece for easy release, but I am told that doing so could lower the absorption capacity of the plaster afterwards. Can someone shed light on the matter? Thanks in advance. Quote Link to comment Share on other sites More sharing options...
neilestrick Posted May 9, 2023 Report Share Posted May 9, 2023 You'll need to wash the mold to get rid of the soap. Danielle Caron 1 Quote Link to comment Share on other sites More sharing options...
Danielle Caron Posted May 9, 2023 Author Report Share Posted May 9, 2023 Just washing the mold is enough, no need to worry about oil residues from the soap? Great news. Thanks. Quote Link to comment Share on other sites More sharing options...
High Bridge Pottery Posted May 9, 2023 Report Share Posted May 9, 2023 Not sure if this is the same as murphy's oil soap but "Potter's Soap (potassium oleate) reacts with the plaster (calcium sulphate) to form calcium oleate, or a 'soap scum'. The 'scum' that forms on the surface creates a nonporous waxy film, sealing the plaster." - https://www.artcoinc.com/potterssoap.php#potters No idea if that means you can't wash it off either. Quote Link to comment Share on other sites More sharing options...
Danielle Caron Posted May 9, 2023 Author Report Share Posted May 9, 2023 There's no potassium oleate in Murphy's soap. Quote Link to comment Share on other sites More sharing options...
Jeff Longtin Posted May 11, 2023 Report Share Posted May 11, 2023 Murphy's Oil Soap is an effective way to seal plaster, temporarily. Depending upon how it is applied it will sometimes just flake off the plaster surface after the plaster has dried. (No need for washing, in other words.) Murphy's, like all soaps, develops a lattice structure only after it is lathered up and then allowed to dry. (After the suds/bubbles have been wiped away.) The drying creates the lattice structure that seals the surface. If one is making a mold of a fired ceramic object, Murphy's doesn't really seal the surface. It sits on top. If the plaster is poured while the Murphy's is still wet it may absorb into the freshly poured surface. If that happens the plaster may become weakened and may erode sooner than normal. If I'm making a mold of something, other than plaster, and I'm unsure if it's completely nonporous, I will spray acrylic paint on the object. (That way I know the surface is sealed.) In mold making, like all things creative, there are "rules" that can make the process more effective. On the other hand, like all things creative, one can break the rules and still have successful outcomes. Roberta12 1 Quote Link to comment Share on other sites More sharing options...
Chilly Posted May 14, 2023 Report Share Posted May 14, 2023 I read that you should use vinegar to help remove the soap. Quote Link to comment Share on other sites More sharing options...
Mark C. Posted May 15, 2023 Report Share Posted May 15, 2023 If you use pure lube made for this it does not hinder the plaster at all- https://shop.clay-planet.com/pure-lube-mold-soap---ip-240.aspx Quote Link to comment Share on other sites More sharing options...
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