clay lover Posted June 2, 2011 Report Share Posted June 2, 2011 Do any of you have this issue, and why do you think it happen? I take great care in slabbing the clay, don't twist or stretch the clay when forming the humped or slumped tray forms, and dry them slowly and evenly on wire racks. They go into the bisque absolutely flat, and then some of them come out warped, some not, and it doesn't seem to matter if they were stacked or laid one by one flat on the kiln shelf. All treated the same from the same slab of clay dried the same, ect. Then some of the warped pieces flatten out perfectly in the glaze? Any ideas? How to you bisque flat work? stacked or not? I don'y mean tiles, but small, pressed in foam ,trays with low sides. Thanks for any input. Link to comment Share on other sites More sharing options...
Chris Campbell Posted June 2, 2011 Report Share Posted June 2, 2011 Interesting info on them flattening out in the glaze firing ... I usually don't bother re firing them if they warp in bisque but now I will try it. As to warping ... It's hard to know since you might have done one of those million things that cause warping ... Which leads to the question of why clay never remembers the good things you do but responds to the millisecond touch with your left thumb? I watched a Chinese slab worker and he only moved the slabs using two ruler shaped sticks ... One on each side of the slab to pick up or adjust the slab. He also did not use any of the clay on the ends. Started all cuts about four to six inches in. Link to comment Share on other sites More sharing options...
Christine Posted June 8, 2011 Report Share Posted June 8, 2011 I am REALLY interested in this post! I have to say, I rarely seem to have a problem with warping, but when I have, I've just trashed the piece and started again. However ... recently I made some highly (and variously) textured wall-hanging pieces, one of which did come out of the kiln warped - I was so disappointed, having invested a lot of time and energy into producing it and could not really understand why it had happened to just the one (of five) pieces. Normally, I would have "chalked it up" but now I just cannot wait to refire with the others (I plan on coating and rubbing off red iron oxide and then clear glaze) and hope I get the same flattening effect that you did with your pieces .... watch this space and thank you Christine Link to comment Share on other sites More sharing options...
clay lover Posted June 27, 2011 Author Report Share Posted June 27, 2011 Well, ladies, it worked again!!! I had several warped trays come out of the bisque, they went in flat. doesn't seem to matter how I stack them for the bisque as to what warps or not. Glazed as usual, unloaded, all but 1 was absolutly flat, cound not tell which had gone in wonky and which had gone in glaze flat. The one was slightly unlevel , and I used a flat grinder on the high corner, and it was fine. SO, don't toss those warped pieces. I do soak for 30 min ast peak temp, and slow cool, soak again at 1900 for 20 , and again at 1700 for 15 min, may have something to do with it??? Link to comment Share on other sites More sharing options...
azjoe Posted June 27, 2011 Report Share Posted June 27, 2011 Then some of the warped pieces flatten out perfectly in the glaze? What clay are you using? How close to it's full maturation point do the witness cones show you get when you glaze fire? Could it be you're firing a little hot and that is causing the clay to relax (slump) from warped back to flat? Link to comment Share on other sites More sharing options...
Denice Posted June 28, 2011 Report Share Posted June 28, 2011 Then some of the warped pieces flatten out perfectly in the glaze? What clay are you using? How close to it's full maturation point do the witness cones show you get when you glaze fire? Could it be you're firing a little hot and that is causing the clay to relax (slump) from warped back to flat? I agree with azoe that you may be firing a little hotter than the maturation point, when I started soaking at the peak temperature I noticed that it would was slightly over firing. I don't have a digitally controlled kiln just pyrometers so I started soaking about 100 degrees below my desired temperture and by the time allowed for the soak I was at temp. Denice Link to comment Share on other sites More sharing options...
clay lover Posted June 29, 2011 Author Report Share Posted June 29, 2011 I'm using several different clays, some Highwater, Some Tucker's. They are rated 5,6 - 8, the cones are a solid 6, 7 is slightly curved, on all shelves. If it was over fired and slumping, wouldn't plate rims, and other such things be laid over? Everything looks great. Link to comment Share on other sites More sharing options...
azjoe Posted June 30, 2011 Report Share Posted June 30, 2011 If it was over fired and slumping, wouldn't plate rims, and other such things be laid over? Everything looks great. One would think, but I have found that I have lots more "movement" in hand built pieces than I do in thrown pieces. I always attributed that to stresses I managed to have in my hand built pieces due to uneven thicknesses, etc., but I really don't know... could be just the round versus rectangular thing for all I know. When my pieces warp it is generally only during glaze firing, particularly when there are thickness variations. If all your clays warp during bisque and then straighten in the glaze firing then you truly have a mystery for sure. Link to comment Share on other sites More sharing options...
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