RachelM Posted January 25, 2022 Report Share Posted January 25, 2022 Hello Everyone, I'm new to the forum. I have been doing ceramics for many years but recently making a lot of flat dishes and plates, mainly with plaster hump molds. I am using Clay Planet Venus White clay fired to Cone 6. Recently having lots of frustration with warping. I handle my slabs as little as possible before I put it on the mold, and dry my pieces slowly under plastic. I can't dry these upside down, because they have scalloped edge treatment. Is there a better clay body that would warp less? Am I firing too fast? My bisque firing takes about 8 hours, and glaze firing takes about 9.5 hours. Any assistance is appreciated! Link to comment Share on other sites More sharing options...
Mark C. Posted January 25, 2022 Report Share Posted January 25, 2022 I cannoit speak to the better cone 5 clay bodies as it not a temp of clay I use. That said if you move your foot out more you will have far less slumping. Its to much in the center to support that overhang . This alone may cure the slumping issue. Try a larger diameter foot Link to comment Share on other sites More sharing options...
oldlady Posted January 25, 2022 Report Share Posted January 25, 2022 the plates look very thick to me. if you try making them a little thinner, with a wider foot, there will not be so much weight to support. Link to comment Share on other sites More sharing options...
neilestrick Posted January 25, 2022 Report Share Posted January 25, 2022 If they're flattening out in the glaze firing, that is a slumping problem, not a warping problem. The clay is getting soft and gravity is pulling it down. A wider foot would help. Link to comment Share on other sites More sharing options...
RachelM Posted January 25, 2022 Author Report Share Posted January 25, 2022 2 hours ago, neilestrick said: If they're flattening out in the glaze firing, that is a slumping problem, not a warping problem. The clay is getting soft and gravity is pulling it down. A wider foot would help. They are not flattening, just warping. I appreciate that so far 3/3 responses recommend a wider foot! Will definitely try that. I think I also need to wrap the edges when I am drying. Thank you! Link to comment Share on other sites More sharing options...
Mark C. Posted January 25, 2022 Report Share Posted January 25, 2022 I would make them thinner as well Link to comment Share on other sites More sharing options...
oldlady Posted January 25, 2022 Report Share Posted January 25, 2022 don't want to harp on my comments but i really believe that when folks start making pottery they hear "make slabs at leas 1/4 inch thick" and they never go any thinner. look at commercial china and see how a normal plate has been designed and made. ignore Pfaltzgraf or however it is spelled. heavy plates stay in the cupboard or go to thrift shops. heavy is not good, thick is heavy, you are working with heavy things and it is just harder on your body. Link to comment Share on other sites More sharing options...
dhPotter Posted January 25, 2022 Report Share Posted January 25, 2022 When drying your pieces you can turn them upside down and let the center rest on a piece of foam, like upholstery cushion foam cut down to fit inside the piece, something thick enough to get the rim off the shelf. You may still want to wrap the rim with plastic. Link to comment Share on other sites More sharing options...
RachelM Posted January 26, 2022 Author Report Share Posted January 26, 2022 Good idea, thank you Link to comment Share on other sites More sharing options...
LeeU Posted January 27, 2022 Report Share Posted January 27, 2022 I use foam in a zillion different shapes and sizes, usually custom cut to fit the project. It is a wonderful way to support the pieces for drying all kinds of upside-down edges, dips, protrusions etc. Link to comment Share on other sites More sharing options...
Callie Beller Diesel Posted January 27, 2022 Report Share Posted January 27, 2022 Even a wadded up towel will work in a pinch. Link to comment Share on other sites More sharing options...
Jeff Longtin Posted January 27, 2022 Report Share Posted January 27, 2022 While I agree a wider foot will help I think your greater problem is that your hump is not deep enough. (tall enough?) Determine what depth you would like your plates to have and then measure the fired results. Increase the depth of your hump mold, by that much, to overcompensate for the warpage. Link to comment Share on other sites More sharing options...
GEP Posted January 27, 2022 Report Share Posted January 27, 2022 I make a lot of slab built plates and trays. I agree with making the slab thinner, the foot ring wider, and the hump mold deeper. Sometimes my plates will still do a bit of “taco shell” warping like yours. This happens when I am using clay that is a bit too soft for slab work. When I handle the slabs they get bent too much, then the bend comes back during the firing. Working with stiffer clay helps, or just wait an hour after you roll out the slabs to let them firm up. Link to comment Share on other sites More sharing options...
Jeff Longtin Posted January 28, 2022 Report Share Posted January 28, 2022 Another thought comes to mind. Clay can warp if its particles are not aligned to the shape its being asked to form. One way to align the particles, on a plate form, is to compress the clay AFTER you put it on the mold. (A potters wheel or banding wheel helps in this regard.) As you have uniquely shaped the clay I would suggest you drape a round, uncut, slab over the mold. Compress it as much as you can with a rubber kidney tool, then allow it to set up a bit. Then cut your shape. A bit of a pain but as much compression as you can afford will really go along way to reduce warpage/distortion. Link to comment Share on other sites More sharing options...
Pine Ridge Posted January 28, 2022 Report Share Posted January 28, 2022 Warping in slab-built pieces is all about how good your slab is. If there is the least variation in the thickness of the slab, the piece will warp. Doesn't matter how you dry it, or how you fire it. An uneven slab = a warped piece. I don't know how you make your slabs, but that is what you need to work on. Do you have a slab roller? A good one, not a toy? Do you roll each slab in at least 2 directions? Do you roll it on thin cotton and carry it around on the cloth to avoid finger stretching? Even if you make your slabs with a rolling pin, you can do these things. And you'll get better at it with practice. Good luck! Link to comment Share on other sites More sharing options...
RachelM Posted January 28, 2022 Author Report Share Posted January 28, 2022 1 hour ago, Pine Ridge said: Warping in slab-built pieces is all about how good your slab is. If there is the least variation in the thickness of the slab, the piece will warp. Doesn't matter how you dry it, or how you fire it. An uneven slab = a warped piece. I don't know how you make your slabs, but that is what you need to work on. Do you have a slab roller? A good one, not a toy? Do you roll each slab in at least 2 directions? Do you roll it on thin cotton and carry it around on the cloth to avoid finger stretching? Even if you make your slabs with a rolling pin, you can do these things. And you'll get better at it with practice. Good luck! Hi Pine Ridge, I don't have a slab roller. I throw / roll my slabs by hand in my garage studio. I did suspect that uneven slabs might be at least partly the culprit, but a slab roller is just not a realistic investment for me right now. I do follow the rest of your suggestions as best as I can, though.. I appreciate it! R Link to comment Share on other sites More sharing options...
RachelM Posted January 28, 2022 Author Report Share Posted January 28, 2022 5 hours ago, Jeff Longtin said: A bit of a pain but as much compression as you can afford will really go along way to reduce warpage/distortion. Yes, good idea, and I need to do more of this. Thank you for the suggestion. Link to comment Share on other sites More sharing options...
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