Handy Goblin Posted February 25, 2023 Report Share Posted February 25, 2023 (edited) Hello everyone. I wanted to create a mold for slipcasting of little figurine. It is very simple object for 2 part mold. As a filler I used stoneware clay and fill exactly half the object, made everything very smooth and nice and everything exactly according to many tutorials I watched. But after demolding my object there is same issue third time in the row. Plaster is not in the half but much lower under the center line I made. I'm using gyprock pottery plaster. My guess is that clay is sucking water out of the plaster, expanding and pushing figurine up. I would appreciate the answer if somebody bumped into the same problem before. Thank you for your time. Edited February 25, 2023 by Handy Goblin Quote Link to comment Share on other sites More sharing options...
Mark C. Posted February 25, 2023 Report Share Posted February 25, 2023 Are you sealing the clay object? You need to. Never seen this. I am not familair with that plaster name but down under is different stuff. Quote Link to comment Share on other sites More sharing options...
Handy Goblin Posted February 25, 2023 Author Report Share Posted February 25, 2023 The figurine is not clay. It is 3D resin print, and yes I'm putting mold soap on it. I do not putting anything on clay. My walls for molding are just plywood also covered in mold soap. Sorry what you mean by down under? Quote Link to comment Share on other sites More sharing options...
High Bridge Pottery Posted February 25, 2023 Report Share Posted February 25, 2023 Not something I have seen before, I wouldn't think the clay is absorbing water and expanding as the feet seem to be affected much worse than the head and I am not sure the plaster stays wet long enough or clay really does that to much of an extent. Down under = Australia Quote Link to comment Share on other sites More sharing options...
PeterH Posted February 25, 2023 Report Share Posted February 25, 2023 I'm having trouble visualising your process. 1) Can you reference one of the tutorials you are basing your process on? 2) You print a hollow figure then "As a filler I used stoneware clay and fill exactly half the object". As I assume you are trying to take a mould of the outside of the figure why not just entirely fill it with clay? (Obviously I'm missing something here.) 3) You seem to be trying to take a casting of the lower side of the figure which is presumably resting on plywood. I'm far more familiar with first taking a casting of the upper half of the figure, with the lower half embedded in clay. As shown in :Mold Making and Plaster Mixing 101http://www.davidwbolton.com/uploads/5/5/1/4/55145091/moldmaking_and_plaster.pdf Then flipping and casting the other side Quote Link to comment Share on other sites More sharing options...
Handy Goblin Posted February 26, 2023 Author Report Share Posted February 26, 2023 I see there is plenty of miscommunication 1.Tutorials I follow mostly are from Hammerly ceramics and VanTiki on YouTube. 2. The printed figurine is solid. As filler I ment clay around the figurine. 3. What you see on picture is demolded object flip around. I do exactly what you posted on picture Mold Making and Plaster Mixing 101 Well I will let you know if I figure it out. Maybe I do something stupid what I'm not realizing PeterH 1 Quote Link to comment Share on other sites More sharing options...
Mark C. Posted February 26, 2023 Report Share Posted February 26, 2023 Sorry I took Sydney to mean in Australia --Now my guess is England-as I have never heard of Sydney as a country If you are claying up the form and its to the 1/2 way point and then you pour the plaster and the line is less than 1/2 way the only way that can happen is the form floats up or gets pushed down depending on whats going on. What type of clay are you using for the claying up? and is the form moving in the process?I did read up on that plster and it looks fine for molds.. I have never seen this issue so go back to basics make sure you clay up to the 1/2 mark -use wet firm clay to clay up.Pour the plaster over a form and clay that has release on it. 3rd times a charm they say Quote Link to comment Share on other sites More sharing options...
PeterH Posted February 26, 2023 Report Share Posted February 26, 2023 Thank you for your patience. Looking at the figure in the as-cast orientation: ... and assuming that the dotted line marks the intended parting-line, and is where the clay was positioned before casting. The current position of the plaster suggests that: - either the figure has moved away from the plaster after casting (perhaps as the embedding clay was pulled away) - or the embedding clay moved to enclose more of the figure during the casting (difficult to imagine, especially given the cleanly cast edge) Can you pull the figure out of the plaster and look at the cast. Is the cast "clean"? How far up the figure would the cast go? Can you push the figure back into the cast. How far does it go in? Obviously any undercuts will hinder the movement of the figure relative to the plaster. Quote Link to comment Share on other sites More sharing options...
Jeff Longtin Posted February 27, 2023 Report Share Posted February 27, 2023 Hello Handy, Not quite sure why this is happening to you. When the "unexpected" happens to me I just roll with it. Rather than try to figure out why this is happening I would simply use this first casting as a "throw away" mold and continue pouring the mold. When you pour the second half it will likely go beyond half way and may hold onto the piece. In this case I would take a small trimming tool and carve back the plaster. (to the line you indicated/prefer) Generally speaking I do not pour molds off clay. (as the embedding material) If the form is complex I may use clay for that first pour but once plaster is poured I use that as the embedding material. (And discard the piece that was poured against clay.) This way I can more easily control the parting line and create a mold with nice tight seams. PeterH 1 Quote Link to comment Share on other sites More sharing options...
Hyn Patty Posted March 1, 2023 Report Share Posted March 1, 2023 Good advice here already but I have a suggestion. Swap out your stoneware embedding clay for oil clay. PeterH 1 Quote Link to comment Share on other sites More sharing options...
Handy Goblin Posted March 1, 2023 Author Report Share Posted March 1, 2023 Thank you all for answers and tips. I switch the clay to more fine one and the issue went away. Now I have pretty good results. Thanks again Hyn Patty 1 Quote Link to comment Share on other sites More sharing options...
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