ZAN Ceramics Posted May 1, 2017 Report Share Posted May 1, 2017 Anyone know what to add to porcelain slip to make it more like an underglaze? I am tying to brush it on to bone dry greenware (cone 6 B-mix clay) before I bisque in order to cover "memory" lines created from the mold. I find that these lines in the clay show up in the glaze fire with all my transparant glazes, so I am trying to add this white underglaze to cover it before I glaze. So far no luck, these darn traces of the mold still show. Link to comment Share on other sites More sharing options...
Chilly Posted May 1, 2017 Report Share Posted May 1, 2017 Are these the fettling lines? If yes, there is almost no way to get rid of them. Somewhere there is a link to (on this forum, I'm certain) a fantastic article which explains how the particles align when settling and drying on slip-cast ware. If the mould lines are really tight and smooth, there is less problem, but what happens is: the particles align themselves with the mould, and then turn into the seam. When you clean the seam at leather-hard/greenware stage, you have now changed the way the particles want to lay, and no matter how well you clean, on firing, the seam will re-appear due to the way the clay shrinks - greater in one direction than the other. The article suggests the cure is to carve out a bit more of the mould line than you think you want, roll a small coil of the same clay, and then press into the mould line !!! Yeah, like we've all got time for that. So, even covering with more slip will not get rid of the lines. I'll see if I can find the article, it does a better job, with pictures, than I can with only words. Link to comment Share on other sites More sharing options...
neilestrick Posted May 1, 2017 Report Share Posted May 1, 2017 Slip is clay, so it must follow the same rules of joining as any other clay. Just like adding handles and such, it must be done at leather hard or wetter. With a thick enough layer you should be able to cover the lines. Link to comment Share on other sites More sharing options...
ZAN Ceramics Posted May 2, 2017 Author Report Share Posted May 2, 2017 Thanks, I have tried those suggestions and still have the darn mold lines showing up when using a translucent glaze (Matte glazes are ok). I am experimenting with a few slips and underglazes so I'll let you know if I solve this. Thanks again! Link to comment Share on other sites More sharing options...
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