Nicky S Posted July 8, 2020 Report Share Posted July 8, 2020 Hi ........ Am wondering If I could fire a solid piece of square porcelain (10 cm x 10 cm ) Thickness approx 6-8 cm .Or will it break / explode ? As I know a hollow sphere needs a breathing hole Thank you .Nicky Link to comment Share on other sites More sharing options...
oldlady Posted July 8, 2020 Report Share Posted July 8, 2020 do not do it is the reasonable answer. how do you imagine the center has, or will have, dried when it is fired? of course it will explode. what is it supposed to be? why would you do this? Link to comment Share on other sites More sharing options...
Nicky S Posted July 8, 2020 Author Report Share Posted July 8, 2020 @oldladyI was hoping to make a small statue with some cuts ( but they don’t go all the way thru )What would be thickest option in your opinion ? Link to comment Share on other sites More sharing options...
neilestrick Posted July 8, 2020 Report Share Posted July 8, 2020 You should really stay under 1.25cm, and even then you'll need to fire slowly. A hollow sphere does not need a hole. As long as it's totally dry you can fire something that is hollow and sealed. Moisture in the clay turning to steam is what causes explosions. When you put a piece in the kiln, even if it's bone dry it will have some moisture in it. You can't get a piece down to 0% moisture when it's sitting in a room that has 50% humidity. So that last bit of moisture has to be evaporated off before it turns to steam. In a thin piece this happens very easily. But in a thick piece it takes longer for the heat to penetrate, and the moisture has to travel farther to escape the piece, so you have to do a preheat to drive off the moisture at a temperature where it won't turn to steam, like 90C or 200F. In a hollow but sealed piece, it takes a really long time for the piece to totally dry on the inside. An air hole helps the moisture to escape, but it's not necessary if you do a preheat for a few hours after letting the piece dry for a long time. Without a hole, the just the expansion of the air inside the piece is not enough to blow it up- it's always from water within the walls turning to steam that causes explosions. In your 6-8cm thick piece, you've also got the issue of expansion and contraction during the firing process, where the outside of the piece is going to heat and cool much faster than the center of the mass, which will cause warping and/or cracking unless you were to fire both up and down extremely slowly. It would probably require a firing that took a couple of days or more. Link to comment Share on other sites More sharing options...
Nicky S Posted July 8, 2020 Author Report Share Posted July 8, 2020 @neilestrickThank you for taking the time to explain the whole procedure Much appreciated and very kind And good to know eg . a sphere doesn’t need a hole as long as dried thru Ive been told otherwise Even a tiny hole spoils the aesthetic I will try hollowing out the piece to advised thickness Nicky Link to comment Share on other sites More sharing options...
Chilly Posted July 11, 2020 Report Share Posted July 11, 2020 I know I really should know the answer to this question, but........... How do brick makers manage to fire bricks that are 200mm x 100mm by 80mm or bigger? It must be the nature of the clay? But I can see why @Nicky asked the original question. Link to comment Share on other sites More sharing options...
oldlady Posted July 12, 2020 Report Share Posted July 12, 2020 funny thing, chilly, there is a brick factory about 20 miles away. they had bricks of all kinds in neat piles all over their many acres. at some point they asked a local potter for help in making new bricks... he did help them learn how to make and fire bricks. apparently the guy who knew how was no longer there to do it. makes me think of Isaac Button. Link to comment Share on other sites More sharing options...
glazenerd Posted July 12, 2020 Report Share Posted July 12, 2020 On 7/8/2020 at 8:38 AM, Nicky S said: Hi ........ Am wondering If I could fire a solid piece of square porcelain (10 cm x 10 cm ) Thickness approx 6-8 cm .Or will it break / explode ? As I know a hollow sphere needs a breathing hole Thank you .Nicky The largest solid porcelain slabs I have fired were 65cm x 2.5cm thick: custom countertop slabs. There are several tricks and protocols you will have to follow starting with your clay. Plasticity level has to be much lower than typical porcelain used for throwing. High plasticity= high shrinkage= higher memory. You will have to customize tile setters to his fire them on edge to avoid drag. You will have to candle them even if you are sure they are bone dry. The cheek test does not work on thick slabs. Finally, you have to customize the firing cycle. T Link to comment Share on other sites More sharing options...
glazenerd Posted July 12, 2020 Report Share Posted July 12, 2020 The sink rail is 25" x 3/4" after bisq firing. Could only find a half slab left from that job. Note: failure rate on this job was almost 15%- not uncommon for big slab work. Link to comment Share on other sites More sharing options...
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