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lisasimmons

Cracked Along Base And Side

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I am having a time with my larger casserole dishes or platters with sides cracking along the bottom edge .  In some of my pieces the entire bottom came apart from the sides.  I checked to see if the bottoms were to thick or to thin.  In all the cases they were not.  Any suggestions on what I am possibly doing wrong? 

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Hand built or thrown? Are you cutting from the Bat or waiting for them to pop off? It is either the way you make them or dry them but more info is needed to determine possible causes.

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What min said plus: how much of this dish/platter is making contact with the shelf? Was it bisqued, then glaze fired? What ramp cycle/s did you use?

Paper or plastic? Large, medium, or small? Would you like fries with that?..sorry, got lost in the moment!

Nerd

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This casserole dish was thrown on a wheel.   About 14 inch diameter.  The crack is along the inside where the sides meets the base.   It was cut and left on bat.  Temperature in building was about 70 consistently.  The crack is showing up in about 24 hours.  The piece was not covered.  

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What clay are you throwing?

 

Using too much water and not keeping the clay compressed enough can lead to more dramatic changes as the piece dries leading to the type of stress cracks you describe.

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Definitely will cover.  However I had another piece exactly the same that was covered and the same thing happened.  I am not sure if that one was cut from the bat.  I don't think it was and I do think that was part of the problem with the cracking.  I will make another casserole dish tonight and cut it from bat, cover it and see if that makes a difference.  Thanks

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Lisa, if you need a lot of water to throw comfortably, then be diligent about frequently soaking it up and keeping everything as dry as you can while you throw, so you minimize shrinkage and stress. Keeping the clay compressed and dry means less open space as the water evaporates and equals denser clay. No guarantee this is your issue, but is something I always do and I have very good success if I follow this rule. When I don't compress the bottom of the piece while throwing and use excess water I will generally get a crack of some sort.

Clark

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What is the bat material? If it's plastic, it is only allowing the interior of the bottom to dry and the exterior of the bottom may be reattaching to the bat. You may have to flip the piece off of the bat, put a couple of sheets of newspaper on the bottom, then re-flip to another bat.

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Bat I used is plastic composite and also compressed fiberboard.  I had cracking using both types of bats.  My husband asked me if a 20 degree drop in temperature could have made this happen. The studio was 72-75 during the day and he thinks it dropped to 62-65 during the night.  What is the ideal temperature the studio should kept at?

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I've never had a problem with low temperatures in the range you are experiencing, when it's warm and the air very dry then things can dry to quickly. My studio is not insulated and when it's cool and the air is moist everything just takes forever to dry, when it's summer I cover everything in plastic left over from the dry cleaner laundry, or wax resist depending...

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What clay body are you using? Smooth white stoneware clays will love to crack on large flat pieces if you're not compressing well. You'll probably have to re-cut the pots from the bats after they have dried some. Maybe even a 3rd time depending on the clay body. In 24 hours after throwing, something that large shouldn't be dry enough to have crack showing up. Try cover the rim with plastic and leaving the center open. If the area where the wall meets the base is a rounded transition, that difference in thickness could be enough to cause cracking. Makes sure that's a well defined corner with even thickness throughout.

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It may be an issue with the way your are throwing the casserole itself. If you are opening up, then deciding you need to be smaller and are pushing the clay back inward as you pull, you may have an uncompressed area in the base corner of the casserole. This will cause a crack between the pulled wall and compressed floor. Try opening a little smaller than the diameter you need then pull the clay outward to the diameter you need and then up, thus moving the clay particles up and around the base in a curve that organizes the particles at the corners, base an side wall. I had this sort of problem with casseroles years ago, and finally after changing a lot of throwing tactics to solve, came up  with that solution.

 

Of course as others have said, slow drying, flip as early as you can, and keep the water sopped up inside.

 

best,

Pres

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I was a member of a studio some years ago and we were having a problem with the recycled clay cracking like your casserole dishes, the clay was difficult to throw also.

 

Seems the clay barrels had developed a pretty good odor after a few years and one day one of the tech's dumped in just a touch of bleach to freshen things up...

 

Killed all the bacteria and the clay lost most of it's plasticity, we wound up dumping a couple thousand pounds of recycle that had already been pugged and bagged. It might have recovered given enough time I guess, but not really worth keeping it around that long.

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I usually buy my clay by the ton mostly because the price is so much better, I have a lot of other interests and don't throw as often as I should so my clay gets time to age a bit and I find the more it ages the better it throws as long as you can keep the moisture level where you like it. The clay always comes much to soft from the dealer for me than I like, so 6mos or a year of age all the boxes packed tight together is what I like. My current batch is about 2 years old and very plastic and throws wonderful.

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