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| Author | Topic: s cracks |
| shevon |
posted 6/8/07 4:17 PM
Hi, I know this is an old subject same problem! S Cracks. I have a student who is getting them in the bottom of her large bowls. Can anyone offer some help? http://anamcre.com pottery studio |
| Al Gray |
posted 7/1/07 1:52 PM
I have had that problem with many of my pieces. What I have read and tried to put into use is to align the clay platelets by raising and lowering the clay while centering. Sense I have been using this method the number of cracks have dropped. There must be other factors or I would not have any more at all. Hope this helps. |
| DebraRay Thompson |
posted 12/8/07 1:29 AM
S cracking, may be due to several factors, clay used, drying process, humidity where you live or in the studio,amount of time or compression used in throwing. Porcelain or porcelain like stonewares, seem to have more problems since partical size is so fine, it is not very forgiving and shrinkage rate is greater,where as, groggier stonewares are more forgiving and generaly shrink less.I'm very picky about the drying processwith my work, as well as, my students pieces. We live in Eastern Colorado where it is very dry most of the time, I perfer to keep things bagged or in the wet box, and flipping it over and over as soon as possiable so it can dry more evenly, I do not handle the piece I flip it between two bats, to prevent warping. I've not had to many problems with S cracking maybe one piece in 1000 pretty good. Several yrs ago I did read in one of the major mags in tips, about compression in throwing. The school of though, seemed to make sense to me, that we spend a great deal more time on pulling up walls and shapeing our pot them we do insureing that we have a good foundation, pulling and shapeing are in essence compressing. I now stress this with my students, Many of us do not spend enough time or effort on compressing the bottom, during opening and before raising the walls. I have my students open up bowls with more clay left in the bottom, in order to go back and forth several times pressing with thumb, spounge, or ribb compressing the clay, most of the time the extra clay is removed or pushed out to the right thickness. Hope this is helpful, not to boring and forgive awful spelling and grammer!DebraRay |
| Rusty |
posted 1/17/08 5:55 PM
The dreaded S crack. I used to get these mostly on plate forms, but I rarely have this issue any more. And it's due to a couple variables. First: Clay selection. As mentioned in other replies, groggier clays will work better for bigger ‘stuff’ that is prone to have S cracks.Second: Proper wedging. I start with a 'rams head' method which is straight wedging and compressing the sides. I then switch to more of a 'snail tail' method. It’s the same as the 'rams head' but with a quarter turn after every push. This forms the clay into a piece that looks like a ice cream cone. This method helps to align the clay particles at the base of the cone, which is the part that will go directly on the wheel or bat.Third: Compressing the base. Coning the clay once it’s on the wheel helps the compression of the base during throwing. This along with the fore mentioned technique of compressing the base by working the clay down from the outside of your base to the inside.Fourth: Throw drier: Too much water at the bottom of your piece allows the particles to separate. This is particularly noticeable in beginners. I can walk into a room and pick out the newbies just by looking at the ring of mud surrounding their workstation. Centering creates a certain amount of slip. I put this slip into a bowl next to my water bowl. Then when working with the base I use the slip instead of water. If I do see water in the bottom, I’m quick to sponge it up and recompress. Fifth: Dry slow. As mention in other posts, make sure pieces dry slow and evenly.Hope this helps,-Rusty http://www.cclay.com Virtual Tour of North American Potters |
| marshall |
posted 2/6/08 10:35 PM
One of the reasons s cracks happen can be due to uneven drying. I tried the new Miracle Bats and one of the things that impressed me with them are that pieces dry very evenly ending the kind of s cracks that are due to uneven drying-The Miracle bats work much better then plaster and plaster hydro- bats I have tried in the past -they are a lot lighter too.-Marshall |
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