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The dreaded S crack

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Well I know this is certainly not a new topic!! I have read everything I can find on S cracks on the interenet. Read some great threads here but I can't seem to beat this cracking thing. It has me pulling my hair out and throwing my pots at more husband who is not a potter and is trying to help me figure this out! Threw one in the bed with him this morning!!HAHAHA That didn't help the crack any. I have really worked on wedging coning and centering felt like I had a major breakthrough in that area! Have compressed and compressed until my fingers bend backwards.....I am now using so little water in the bottom of a pot I am amazed at myself. My forms are getting much better and more even but by no means are they all consistent. I do have a little bit thicker bottom than I need in a lot of cases and I am sure you all will say that is probably the problem. I have tried cutting things off the bats .....wiring them but leaving them on the bats plastic bats and the ones that look like particle board that are suppose to help....I have turned them brought them in the house trimmed and not trimmed......prayed over them and watched them moved them .......and not touched them.....I dont know what else to do!!! I use mostle Raku Clay I get from my instructor and speckeled brown stone..sometimes little loafers althought not lately I'm out. I just want to cry because now my peices are looking so much better but they crack.....Id say one out of three ...... I have no problem with mugs or tumblers just larger peices bowls and platters.

 

Please help I have not covered the last things I made just brought them in the house so should I have covered them and put them?

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Well I know this is certainly not a new topic!! I have read everything I can find on S cracks on the interenet. Read some great threads here but I can't seem to beat this cracking thing. It has me pulling my hair out and throwing my pots at more husband who is not a potter and is trying to help me figure this out! Threw one in the bed with him this morning!!HAHAHA That didn't help the crack any. I have really worked on wedging coning and centering felt like I had a major breakthrough in that area! Have compressed and compressed until my fingers bend backwards.....I am now using so little water in the bottom of a pot I am amazed at myself. My forms are getting much better and more even but by no means are they all consistent. I do have a little bit thicker bottom than I need in a lot of cases and I am sure you all will say that is probably the problem. I have tried cutting things off the bats .....wiring them but leaving them on the bats plastic bats and the ones that look like particle board that are suppose to help....I have turned them brought them in the house trimmed and not trimmed......prayed over them and watched them moved them .......and not touched them.....I dont know what else to do!!! I use mostle Raku Clay I get from my instructor and speckeled brown stone..sometimes little loafers althought not lately I'm out. I just want to cry because now my peices are looking so much better but they crack.....Id say one out of three ...... I have no problem with mugs or tumblers just larger peices bowls and platters.

 

Please help I have not covered the last things I made just brought them in the house so should I have covered them and put them?

 

 

A few questions about your pots. Is the "s" shape in all of your forms, or in the ones that are with wide bottoms? If in all of the forms, then I would say that you need to establish a base cross section and compress that with your fingers repeatedly before the first pull. If it occurs in a form that has wide base area, use a rib to help you compress the base. I like a firm, not hard, rubber rib to move back and forth across the base. I also make certain to establish a square base/wall transition. Platters are a real problem in the beginning, throw with softer than usual clay,as this allows for easier across the base compression, and don't compress at the end, in the beginning before opening up. Definitely with the rib I mentioned. Try to have 3/8 to 1/2 inch thickness on the base when finished with compression-depending on whether you are trimming the pot, how large the base is, and what type of form you are throwing. You may find the Van der Gilder book with throwing projects published by DYI helpful for you learning experience. Continue with your efforts, practice will get you there.

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Compression is definitely essential, but another common issue for throwers in their early years are uneven walls. In particular, new throwers tend to leave extra thickness near the transition between the floor and wall, or around the footring. When there's extra clay there, the thicker area dries more slowly, it is not shrinking as fast as the middle of the floor, and the floor splits open.

 

Throw and trim a pot as usual, then take a cutting wire and cut it in half from bottom to top. Look at the cross- section to see if there are any thicker areas. I make all of my intermediate wheel students do this on a regular basis. They hate it, but it's important.

 

Mea

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Not sure if I can help I'm a newbie here but when your compressing are you compressing in the right direction? From outer bottom edge back to the center. Usually a few times is good. Are you lettting your ware dry properly. If it's drying to fast or even if your ware is drying unevenly or a combination there of could be a culprit because you sound like your doing everything correctly. After I spin my piece I cut the bottom of my ware but leave it on the bat and cover completley with plastic sometimes two plastic bags depending how dry my room is. Then after a day or two i cut the bottom again with the wire and flip my pot over and recover for another day by then it's usually leather hard ready to trim. After trimming I cover back up for a day or two and then set out uncovered for the rest of the week to completely dry out and prepare for bisque. When I bisque I fire to 04 real slow usually just over 13 hrs and everything usually comes out real nice. Drying slow and evenly is usually key. I have used a clay body type once that didn't cooperate with me so I quit using it. I get my clay from a local supplier now and works well. And if your working with multiple clay bodies make sure your work area is (from your wedging table to your wheel) completly clean before switching to another clay body. Hope this helps and you overcome the cracks. Can't stand it myself when that happens but as I was taught when you make a piece you have to be willing to give up the piece. It's such a long ride to the finish alot of variables can happen trying to make a piece come out the way we envision. Nice thing about clay. Just reclaim it and try again.

 

 

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If nothing else works add a little paper to the clay. It's easy because you only need a small amount to make difference and a small amount of paper will not change the look or feel of your clay--all it will do is possibly stop the cracking. Just make a pound or two of paperclay any way you want (For this small amount I just put toilet paper and hot water into a blender and when the paper is pulp add pinches of clay until I have a thick slip that is then poured onto plaster to dry so it can be wedged up as a one or two pound ball of paperclay.) and wedge it into 20 or so pounds of your regular clay. Wedge until it is thoroughly mixed. If that doesn't work you can try adding more paper to your clay or sacrificing your husband to the god of clay.

 

Jim

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Thanks to all that replied.

Pres I did compress after evertime of opening and pulling and alot at the end. Why is that wrong?? Yes the s cracks are mostly in my wider bowls and platters. I have used ribs off and on but did not this time just fingers pressing really hard. Guess I should do both. No my bottoms are not perfectly even with the sides. Im not there yet but getting better.

 

Offcenter Thanks for the explaination I was wondering what paperclay was.. that is an interesting fix to try sometime if things don't improve I may give it a shot.

Dagwood I cut my things about the same as you do however I think my big BooBoo this time was not covering the three bid pieces. I usually dry things in my studio and cover them or put them in a drying cabinet but it has gotten too cold so I brought them in. I have working on mugs for so long I got in the habit of covering them to keep them workable until I could get handles and embelishments on them. Since I wasn't putting handles on or embelshing these I didn't think to cover just to slow drying duh........ So many thing for this old brain to remember.

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Interestingly, I have been warned about, read about, and even seen a dreaded S crack, but, it spite of being a somewhat new potter, I've never experienced one. (Now I have probably jinxed myself) I must say that I don't compress very firmly, just lots. So maybe don't press so hard...

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Thanks to all that replied.

Pres I did compress after evertime of opening and pulling and alot at the end. Why is that wrong?? Yes the s cracks are mostly in my wider bowls and platters. I have used ribs off and on but did not this time just fingers pressing really hard. Guess I should do both. No my bottoms are not perfectly even with the sides. Im not there yet but getting better.

 

Offcenter Thanks for the explaination I was wondering what paperclay was.. that is an interesting fix to try sometime if things don't improve I may give it a shot.

Dagwood I cut my things about the same as you do however I think my big BooBoo this time was not covering the three bid pieces. I usually dry things in my studio and cover them or put them in a drying cabinet but it has gotten too cold so I brought them in. I have working on mugs for so long I got in the habit of covering them to keep them workable until I could get handles and embelishments on them. Since I wasn't putting handles on or embelshing these I didn't think to cover just to slow drying duh........ So many thing for this old brain to remember.

 

 

Over the years I have found that compressing in the end can lead to problems in the side walls of the form-little digs, and undercuts where I don't need them. Full compression of the base before pulling is really all that is needed. Beginners sometimes rush to the pull, without realizing that setting up the base for the pull is really one of the most important things to do for success beyond centering. For those large platters, try the wetter clay, wedged well, centered well, establish your thickness for the base with a slight outside donut for you rim, then compress it with a rib going back and forth inside of donut to center and back. then pull your rim and flatten that to finish the platter. Wet clay helps to get better compression over the wide base.

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Compression! It's really the best answer. If you're getting cracks with Raku clay, then you definitely aren't compressing enough. Right after you open the bottom diameter, go in with your fingers or a rib and compress it well. Second, if your pots are adhering to the ware boards or bats, cut them loose well before they approach flipping stiffness. If they can't move on the bat as they dry and shrink, they will crack. Third, make sure you are drying the upside down after they are trimmed. They will dry much more evenly that way. Compression!

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I've heard numerous times that pie plates are one of the hardest items to make because they get S cracks so often in them. Someone even told me they put their's in a plastic bag and let it dry over three month time. I've never had a problem with S cracks even in my pie plate, I don't even compress is that much. I just use my finger to make sure that the thickness is even about 5/16 inch and then use an old credit card to make sure it's smooth. I then put them on a shelf and let them dry. The only time I had any S cracks in anything and it was a bowl was when I left some water in the bottom.

 

 

Bobg

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  • WOW Bobg that is awesome! I have also been told that recently about pie plates. I am currently nursing 2 along drying very slowly left in plastic 3 days then let them come out today recovered them tonight. My biggest one is doing well after I covered it and let it sit about 4-5 days then uncovered. They dont fit in my small drying cabinet but I am going to fix that soon. DO you dry your wares in a stable enviornment??

 

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I remember having a run of S cracks when I was learning. It wasn't in the very beginning, but after I was getting a little better. My teacher had me work on 2 things, not sure which one worked, but I still remember to be mindful of both. The first was compression, other folks have talked about that already. The other was my wedging. Be aware of the direction in which the spiral of your wedged clay is turning in relation to the direction of rotation of your wheel. If you wire/slam wedge then it shouldn't be a problem, but if you wedge in a manner that creates a spiral in your clay, try not to have it spin/tighten in the same direction as your wheel, they should spin in opposite directions to cancel each other out, or just not tighten up the spiral any more. This is so it doesn't want to "unwind" quite as much while firing - pay most attention with your teapot spouts, it does make a difference. Hope that makes sense. I think of it as the outside "lip" of the spiral is static, and the direction of my wheel needs to unwind it. Maybe that was to keep me from not overthinking the compression or to just make me work on my wedging a little, but one of them worked and now the odd crack I have is from breaking rules and putting something in the kiln wet or something else blatantly bad. :)

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Slipped I have been working diligently on wedging and coning and I do think that is going to help. I am a little confused by you saying to go the opposite way of the spiral I was told to make sure it was all going in the same direction. Now I am confused can others also weigh in on this ......???? Thanks for your help.

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I never wedge my clay. When I get it, it'a always about the right consistency, I just weigh off what I need to put it on the wheel. Occationally I will wedge some that I've reclaimed, but not very often. My brother has been throwing pottery for 35 years and he does it the same way.

 

 

Grayfree,

 

I just work in my old shop, not heated or insulated. I just put items on the shelf and let them dry. Mugs are different during the summer I cover them for a couple of days after I attach handles. I bought an old commercial restaurant warming oven one time with the thought of making into a smoker for turkeys and sausage, never got that far. During the winter I store my clay (1000 pds) in half and use the other half to put my pots and glaze in. I have a light bulb inside that has a thermostat controlling the light bulb for heat and it comes on at 40 degrees so nothing freezes. Occasionally I will bring pots in the house if I can't get enough in the warming oven.

 

Bobg

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Oh, the dreaded S crack! I had a run of 18 pie dishes. Five of them developed S cracks and had to be smashed. I revisited my wedging technique. After making the spiral into a cone, you compress the bottom of the cone by rotating it and pressing down on the wedging table. Just an added step, but it solved the problem. I also compress the inside bottoms when I throw, but I use a straight wooden rib.

Good luck.

TJR.

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When I first started in pottery, using a local clay I dug and prepared, I had a lot of S cracks in plates. I started throwing on pieces of canvas. Cut under the canvas to release the pot off the bat or wheel. There's no stress on the clay from the cut-off wire. The canvas easily peels off the pot when you are ready to turn. The base of the pot is evenly flat - you may need a bit thicker base if you want to turn a footring.

Cheers. Graeme.

 

 

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That is a good question Ben. I use Raku clay......Little Loafers and Speckeled brown stone. Mostly what is cracking is the Raku and Little Loafers and reclaimed clay. Little loafers maybe a tad more. Yes they are all commercial except the reclaimed which I haven't used that much of.

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OK I AM A TOTAL IDIOT. I HAD THREE PIE PLATES IN DESCENDING SIZES I HAVE been NURSING ALONG FOR ABOUT 2 1/2 WEEKS NOW. TURNING SLOWLY GOT THEM TRIMMED COVERED ....UNCOVERED ALL GOING VERY WELL UNTIL IDIOT THAT I AM TOOK THEM OUT TO MY STUDIO OVER THE WEEK-END BECAUSE THEY "WERE FAR ENOUGH ALONG TO BE OK" WELL IT GOT DOWN IN THE 20'S LAST NIGHT AND IN MY STUDIO IT PROBABLE GOT DOWN TO HIGH 30'S OR LOW 40'S. WELL QUESS What BOTH HAVE BEAUTIFUL S CRACKS THIS MORNING ALONG WITH 2 TUMBLERS I HAD THROWN AND FORGOT AND LEFT THEM OUT ON THE COUNTER!!! WELL IF I HAVE LEARNED NOTHING ELSE EVERYTHING IS COMING IN THE HOUSE IF IT IS BELOW 60!!!! UNTIL THE SPRING I AM SO TIRED OF LOSING PEICES!! AT LEAST I THINK I HAVE THE CULPRIT FIGURED OUT.........TEMP!! Oh I left the largest pie plate in the house uncovered now....NO CRACK!

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You are not an idiot! You are having a bit of a problem and you are allowing it to freak you out!

 

It is hard to attempt a diagnostic this way. You are throwing these plates, right? I am going to try to explain a method I learned as best as I can. I learned it from just looking at an image of hand placement while throwing a plate. I am assuming you are right handed.

 

Wedge a ball of clay. After you have centered the clay, speed should be about medium to slow, open it up to a low bowl, leave about an inch (+-) on the foot so you can cut it off the bat and have room to trim. Use the heel of your right hand to push the clay down and out starting from the center moving to the left. Use your left hand to steady and hold the outside as you push with the right hand. Push out til the two hands meet. Use the fingers on your right hand to form the type of rim that you want. Practice this several times over and over til you get it.

 

After cut off, I leave the plate on the bat until it has firmed up a little bit. Then I remove the plate from the bat and cover with plastic for about a day. Then invert it to trim the foot. Then I sit the plate on a shelf to dry.

 

The plate throwing method is from the book Pottery A Basic Manual by Cora Pucci, Little, Brown and Company Publishers 1974, pg 94.

The book is out of print. Try to borrow it from the library or buy it on line.

 

I have used this throwing method for 37 years and I have never had an 'S' crack. I thought I could provide the image from the book but it would be a violation of Ms Pucci’s copyright.

Stop fussing at the clay, the plates and your husband, bad vibes won't help. If you get an 'S' crack which I doubt, but if you do, consider changing to a more friendly clay body.

 

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