elisethomas Posted May 12, 2014 Report Share Posted May 12, 2014 I'm wondering if I could get some advice on crackle glazes. I use a few different low fire commercial crackle type glazes on a regular basis, have been using the same ones for a few years now. The trouble I am having is with obtaining consistent crackleing. I seem to have an almost 100% sucess rate with my own thrown pieces, but much more variability with my cast pieces. The cast pieces are all low fire white earthenware (the same as my thrown pieces), but the glaze can behave very differently on them. It may crackle completely, partially, in one or two spots or not at all. I have tried many, many test firing to see what factors may be affecting my results, but with no luck so far. What works one time doesn't work the next. Would anyone have suggestions for me as to what may be causing the variability or factors I may have overlooked? Thanks much! Link to comment Share on other sites More sharing options...
Min Posted May 12, 2014 Report Share Posted May 12, 2014 Hi and welcome to the forums! Couple things come to mind, first off, I’m guessing the casting body is a different body than the one you throw with? I don’t just mean the same body that is deflocculated for slip casting. If so then I would guess your throwing body has a lower COE therefore crackle (craze) glaze is more effective on that body. Are the slip cast pieces thinner than the thrown ones? Thin bisque will take up less glaze than thicker bisque and the thinner glaze layer would be less crackled (crazed). Link to comment Share on other sites More sharing options...
elisethomas Posted May 12, 2014 Author Report Share Posted May 12, 2014 Hi and thanks Yes, cast pieces are of a different body. They are actually thicker than my thrown pieces in most (but not all) cases. I have had the same suspicion about the COE effect, however I'm still puzzled about why the crackle works perfectly sometimes. I guess that's what leading me to believe I can make this combo work as desired if I can just figure out the puzzle! Link to comment Share on other sites More sharing options...
Min Posted May 12, 2014 Report Share Posted May 12, 2014 Was the glaze thicker on the cast pieces that worked? Were they in a cooler part of the kiln? Were the ones that didn't work over a wash or underglaze? If all else fails have you tried adding some high expansion frit to the glaze for the cast ware? Link to comment Share on other sites More sharing options...
elisethomas Posted May 12, 2014 Author Report Share Posted May 12, 2014 Nope, I should have mentioned, what I have tested so far. Kiln placement, firing speed, glaze thickness, remixing glaze and changing glaze batches have not seemed to matter. Nor has multiple kiln shelves vs single, venting the kiln or dampening the piece before glazing. Can you tell me more about high expansion frit? I'm not sure what that is. I did try some clear borosilicate frit at one point, but it did not fully melt at 06. Link to comment Share on other sites More sharing options...
Min Posted May 12, 2014 Report Share Posted May 12, 2014 Can you tell me more about high expansion frit? I'm not sure what that is. I did try some clear borosilicate frit at one point, but it did not fully melt at 06. To make a glaze craze you need to add a high expansion material. So adding a frit with high sodium and low alumina, like Ferro 3269 or 5301 would raise the expansion. Both of these melt in the range of ^06 and ^01. Since you are right on the edge of having your current glaze work you probably wouldn't need much. A line blend would be the quickest way to determine how much you need to add to get the crackle you are looking for. Link to comment Share on other sites More sharing options...
elisethomas Posted May 12, 2014 Author Report Share Posted May 12, 2014 Perfect! thanks very much for the help, that will definitely give me something new to try. Link to comment Share on other sites More sharing options...
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