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Hi, I have this problem of cracking or clay splitting when throwing in the wheel, pls find the attached picture and also, after firing at cone 08, the clay has a lot of surface cracks and sometimes structural cracks pls find the attached pic, pls advise why this is happening and how to avoid this in future. Thanks.

WhatsApp Image 2018-04-10 at 4.05.53 PM.jpeg

10.jpg

08.jpeg

WhatsApp Image 2018-03-29 at 11.08.17 AM.jpeg

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Hi and welcome to the forum!

Judging from that first shot especially, you're leaving entirely too much water in the bowls while you're throwing them, and the clay looks overworked or too wet. It looks like your clay has a low tolerance for water in the bottom while you throw, and you need to clear it out more. The second picture looks like not enough compression on the bottom, and perhaps leaving a skim of water on the inside.

In the third picture, did you leave a film of throwing slip on the inside of that bowl or line it with a layer of Terra sig? It looks like there's some kind of layer of fine clay particles on the surface, but it's not something I can gauge properly from a photo. Do those cracks go all the way through the pot, or are they just on the surface?

The fourth image I can see the cracks are structural. It makes me wonder about how damp your pots are when they go in the kiln, and how fast your bisque is. Do you control your own firings, or is someone else doing it for you? Do you live in a humid area?

Also, what kind of clay are you using? You mention terra cotta, but which brand or recipe is it? Do you throw with a rib at all?

Edited by Callie Beller Diesel
Clarification on a question.
Gokul and Rae Reich like this

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Just a couple guesses but perhaps the clay was over-wedged before you began to throw, AKA over-worked so the clay particles are separating. Possibly your clay has a low elasticity. Possibly the drying process was rushed. 

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On 4/10/2018 at 9:23 PM, Callie Beller Diesel said:

Hi and welcome to the forum!

Judging from that first shot especially, you're leaving entirely too much water in the bowls while you're throwing them, and the clay looks overworked or too wet. It looks like your clay has a low tolerance for water in the bottom while you throw, and you need to clear it out more. The second picture looks like not enough compression on the bottom, and perhaps leaving a skim of water on the inside.

In the third picture, did you leave a film of throwing slip on the inside of that bowl or line it with a layer of Terra sig? It looks like there's some kind of layer of fine clay particles on the surface, but it's not something I can gauge properly from a photo. Do those cracks go all the way through the pot, or are they just on the surface?

The fourth image I can see the cracks are structural. It makes me wonder about how damp your pots are when they go in the kiln, and how fast your bisque is. Do you control your own firings, or is someone else doing it for you? Do you live in a humid area?

Also, what kind of clay are you using? You mention terra cotta, but which brand or recipe is it? Do you throw with a rib at all?

Thanks for the reply Diesel, We havent use any slip on the clay and we keep the pieces for firing only after its completely dry and sometimes the cracks are just the surface cracks and sometimes its structural cracks, And yes we are doing our own firing with skutt kiln and the pieces are fired at cone 08 in medium fire setting which is I guess its 150 D / hr.

Basically I m from India and the clay which we are getting locally in powder form, we process and filter it with 100# (sieve) and pug it and we are using it and selling it all over india for the studio potters and for the schools all over india., and yes the clay seems like lacking of plasticity and we are adding 2% of bentonite to it to make sure the clay has fine plastic particles and as well as the plasticity.

yappystudent likes this

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The clay looks short as we say and needs to be more plastic. It looks like to much water is being used too throw it. This will also make it crack more. I would add more materials to make it more plastic and  age it and use less water when working with it.

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