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OTMS

Cracks in press-molded work

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I made some small bisque molds.  I am pressing clay into the molds and making small rounded cups.   Sometimes there are cracks in the outer surface when I take it out of the mold.  The cracks do not seem to go through to the inside.  I fill these in as best I can, and some cracks may be from these reappearing as the piece dries.  Other cracks seem to be new.  

I allow my work to dry slowly to try and prevent cracking.    I am having a high rate of failure and wish I could find an answer.   I do not have a wheel or a place for one and the press molded pieces are mostly what I am doing.  Is it from inconsistent thicknesses.  Also, I try using just one solid piece of clay instead of piecing it together.  I am using Standard 240, Cone 6 clay.  Maybe something groggier would work better...not sure I want to go that route but may try that.

Edited by OTMS
Changed "plaster molds" to "bisque molds".

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I have this problem also using the small bisque molds I've made when the clay is too dry. The bisque sucks the water out of the surface of the clay so quickly that by the time I've finished pressing the lump totally in there it's made cracks in the surface. I've tried different work arounds, this mainly happens with press molds that are fairly deep and detailed, like faces with noses that stick out. There might be better solutions but using wetter clay and spraying the mold with water seem to help. 

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clay lover,

I think folding is part of the problem, but some cracks are very thin hairline.

 

yappystudent,

The clay I am using is a bit dry.  I will try some moister clay and spray the mold with some water like you are suggesting.  Now that you mentioned it, the molds I have been using are bisque, not plaster.  I will edit my post to reflect that.

Thanks

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