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Hi everybody! I am a beginner in ceramics. Could anyone please consult me on one issue? If I use a thermoresistant clay and burn it at 1050 C, will it be less thermoresistant than if I burn it at 1300C? Can I cook for example coffee in a pot burnt at 1050 at all?

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The short answer is no; at 1050C the clay body is only fused. Vitrification begins at 2050F, and increases up to 2190F. The type and amount of fluxes used determine the final vitrification temp.

thermoresistance, commonly known as thermo shock in the States is a broad term that encompasses several formulation variables. I will not bore you with the details. Except to say thermoresistnt bodies which are more commonly used in raku, salt, or wood firings begin with switching out much of the silica with pyrophyllte. These bodies are not necessarily intended for functional use ( food use). Ovenware and or flame ware bodies however are formulated for food use.

additional note: the expansion of these bodies are much lower than traditional porcelain/stoneware bodies. This translates to buying or mixing glazes specifically formulated to match the lower expansion rates. 

Nerd

Edited by glazenerd
My A seems to be sticking on this keyboard.

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20 minutes ago, glazenerd said:

The short answer is no; at 1050C the clay body is only fused. Vitrification begins at 2050F, and increases up to 2190F. The type and amount of fluxes used determine the final vitrification temp.

thermoresistance, commonly known as thermo shock in the States is a broad term that encompasses several formulation variables. I will not bore you with the details. Except to say thermoresistnt bodies which are more commonly used in raku, salt, or wood firings begin with switching out much of the silica with pyrophyllte. These bodies are not necessarily intended for functional use ( food use). Ovenware and or flame ware bodies however are formulated for food use.

additional note: the expansion of these bodies are much lower than traditional porcelain/stoneware bodies. This translates to buying or mixing glazes specifically formulated to match the lower expansion rates. 

Nerd

Thanks a lot for such a detailed answer. Then could you tell me, can I at least use pottery made out of this clay and heat-treated at 1050 C. I mean such pottery as mugs, cups, plates and so on? The problem is that I have 10 kilograms of this thermoresistant clay and at the same time I do not have an oven, which could treat it at 1300 C. So, can I use this clay just to make mugs, plates an so on?

Edited by Kseniia

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In the UK, clay fired to 1050c is known as earthenware.  99% of the mugs, plates etc sold in pound shops will be earthenware.  So the answer is yes, but they will need to be glazed.

 

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37 minutes ago, Chilly said:

In the UK, clay fired to 1050c is known as earthenware.  99% of the mugs, plates etc sold in pound shops will be earthenware.  So the answer is yes, but they will need to be glazed.

 

Thank you!

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2 hours ago, glazenerd said:

Ksenlia:

do you perhaps have a link to the clay you re currently using? Would like to see the specs.

Tom

Hi, I have just received an answer for my inquiry from the manufacturer of this clay Witgert. Here it is: "Thank you for your e-mail. I think you use our body no. 120.7? So the best thermal shock resistance will be in the range 980-1200°C. Higher temperatures up to 1300°C are possible but the thermal shock resistance will decrease"

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20 minutes ago, Kseniia said:

Hi, I have just received an answer for my inquiry from the manufacturer of this clay Witgert. Here it is: "Thank you for your e-mail. I think you use our body no. 120.7? So the best thermal shock resistance will be in the range 980-1200°C. Higher temperatures up to 1300°C are possible but the thermal shock resistance will decrease"

What do you think? Does it also mean that if I treat this clay between 980-1200 C it will not only have best thermal shock resistance but it will also have best refractoriness (flame resistance, heat resistance)? In other words, will an item made of this clay and treated at 1050-1070 be ok for cooking on a gas stove (for example, for making coffee)?

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2 hours ago, Kseniia said:

In other words, will an item made of this clay and treated at 1050-1070 be ok for cooking on a gas stove (for example, for making coffee)?

I looked up the clay you are using and it appears to be sold as a flameware body. There are other factors in making flameware other than the claybody. The shape of the pot and the glaze that are used are also very important. Huge risks involved and lots of testing will be needed. Article that touches on the subject by a potter well known for making flameware here.  Flameware is not something that many potters make due to the inherent risks involved.

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Ksenlia:

after reading the specs on your clay: it will not vitrify at 1000C. It is a high alumina, lower silica body: ovenware for certain. Sorry for the bad news. You would have to find a glaze with much lower expansion, not sure if they make one commercially. As min pointed out, oven ware is a niche commodity. Chilly's suggestion of using earthenware would be good for starting out. You can certainly use it to practice throwing and glazing: but it will not be remotely food safe.

nerd

 

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On 5/1/2018 at 12:34 AM, glazenerd said:

Ksenlia:

after reading the specs on your clay: it will not vitrify at 1000C. It is a high alumina, lower silica body: ovenware for certain. Sorry for the bad news. You would have to find a glaze with much lower expansion, not sure if they make one commercially. As min pointed out, oven ware is a niche commodity. Chilly's suggestion of using earthenware would be good for starting out. You can certainly use it to practice throwing and glazing: but it will not be remotely food safe.

nerd

 

Thanks a lot. But what do you think, will it be ok just for simple mugs, plates and cups?

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