My first teapot cracked- Glaze fire to Cone 10 stoneware with Celadon over white glaze. Why? How to avoid?
reddit.com/gallery/wl2at4
reddit.comPosted Aug 10, 2022, 4:46 PM UTC
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reddit.comIt could be the kind of clay you used was made for low fire or the kiln was opened too soon and it was shocked and cracked
Run your finger over the crack that goes into the glaze and see if it’s smooth or kinda sharp, if it’s sharp it happened during the cooling process/after the firing bc if it happened during it would smooth into the crack
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Was going to second this about the kiln being opened too soon and not having enough time to cool. Looks like a post firing crack. I wouldn't worry about glazing unless the inside really pooled a lot (many people just glaze the inside of things and leave the outside raw, don't let this hold you back from doing that if you like it).
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I’m taking classes at an art center we can only use the clays they have on site… all tested to fire at cone 10. They only fire to cone 10 (for the glaze firing). I heard it crack so it was caused by me. Several other items from the same kiln firing came out fine. I tested the one of the mugs I made with hot water and it did fine, though I did run it under warm water first.
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Wait you heard it crack? When?
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When I put the hot water in. I’ve made a few mugs and haven’t had that happen before, so I was questioning what I did to cause the teapot to crack.
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Ahh, well if it was cold when you poured the water in that sudden temperature change could have caused it. Or there was a hairline crack there before from something in the firing process, and the temperature change just made it worse.
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Looks like the pot couldn't take the uneven tension of your glaze application. Sucks. Leaving stuff partially glazed is really fun. You could try leaving the inside unglazed next time you do something like this. Many teapots have unglazed interiors. That said, you could still run into the same sort of issue.
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If it has the same glaze on the inside at about the same thickness as everywhere else then this is not really reasonable performance and the glaze and body don’t fit each other and you will always be fighting that.
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Always warm up ceramic before putting boiling water in. It gets shocked when it’s cold and building water is added, causing cracks. Also, I agree with part of the previous comment where is is mentioned the glaze ran on the inside- when glaze is pooled too thick it also cracks/ is more susceptible to cracking.
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Where did it crack?edit: second picture didnt load at first could have been too thick or uneven towards the bottom and didnt contract evenly during cooling of the kiln
On the bottom, on the unglazed part. This hasn’t happened with my mugs. I just want to avoid this happening again.
As for thickness, it’s slab built, so all the slab pierces were the same thickness.
I'm assuming that the inside is completely glazed.
Because it cracked where it's not glazed on the outside, but is glazed on the inside I think that's the cause. I forget the name for that, but I've seen it before. There's an actual name for this defect.
I'm also guessing that the glaze is thickest at the bottom of the interior of the pot. The glaze ran a bit, so even if you had a perfectly even cost on the interior when it went into the kiln, it's thicker on the bottom now.
Glazing only one side of a piece can cause stress on the clay. Because it's slab built, it's likely fairly thin and not as compressed as a thrown pot, all contributing factors.
The solution is pretty easy, glaze both sides.
Edit: Also possible that the slabs weren't compressed enough and this is from lack of compression. But I don't do much slab building and could be wrong about that.
It's called Dunting. The expansion and contraction coefficient differs enough between the glazed and unglazed surfaces to cause a fissure. Can also happen with two drastically different glazes.
Didnt know it was slab but this person is spot on
Thank you, I was wondering if this was the issue. I will try again with it glazed all the way on both sides. I do compress after I roll out the slab pieces, and at the end when I’m smoothing out imperfections. I’m new to this though, so my technique is not mastered.
Indeed had this trouble aswell with my most beautiful potter's choice glazes where I left 2 cm unglaced. After firing i had my coffee on my lap because the bottom part popped off^^ For not loosing the astethic of your pot just glaze less coats inside. I don't know your coat numbers but i reduced mine from 5-6 to 3-4 and it never happened again. Also you can apply only for example 2 on the bottom but a 3th on the rim inside.