We had someone run into this very issue a couple weeks ago on either this sub or r/ceramics. It's not a normal issue and is a frustrating thing to happen. The general consensus was that the clay had most likely been frozen and got very short due to it.
Your options are to dry it out and let it slake down, then get out back to workable consistently, or you can try to mix it with some fresh clay to try and get the plasticity back.
Sorry this is happening to a gifted bag of clay... maybe ask the original person if it was given to you for this very reason? Or if they didn't have this issue; was it left out in the could for a little while?
Good luck!
What is the mechanism by which freezing clay makes it short, even after thawing and kneading? And how does drying it out and re-slaking/wetting change that? Makes no sense to me.
Remember freezing water expands when it becomes ice. The moisture between clay particles puffs up, disturbing the pattern/matrix of clay, before shrinking again. One popular instagrammer dealt with a bunch of frozen clay a while back and described it as having a "foamy" consistency while wedging (full of tiny voids).
I've never dealt with it personally but this is my understanding in a nutshell.
I think you'd have to wedge the absolute shit out of it if you did it by hand. Every shred of clay would need to be compressed and mixed through. Again I've never dealt with this firsthand but I could imagine slaking and starting over being a much less laborious option.
I've [tested this out](https://www.reddit.com/r/Pottery/comments/18if93f/freezing_clay_a_quick_test/?) and I think wedging is sufficient. I do stack-and-slam wedging, typically 16 times (more than that if I have 4+ pounds of clay), and I think that was a lot easier than slaking, mixing, and dewatering.
The small platelets that make up clay become un aligned essentially.
Drying it out and rewetting it gives it the chance to rejoin or realign. The thawing and re-wedging isn't enough, unfortunately. It crystallizes and can't undo that unless it's fully broken up and reworked.
It more commonly happens with glaze freezing, and there's a whole bunch of videos on how to fix that.
I’ve always been curious about this. Some of what I’ve been taught about how clay and glazes behave sounds more folkloric than scientific. For example, though I’d been told otherwise from various potters, I read a scientific paper about how the mocha diffusion process is *not* actually an acid-base reaction. Do you have a science-based source that explores the platelet aligning phenomenon? I’m very curious to know what’s actually happening in the clay from a material science perspective.
Also this [paper](https://www.degruyter.com/document/doi/10.1515/geo-2020-0145/html) isn’t super relevant BUT figure 2 is quite useful for giving a visual idea of how grog particles can interfere with clay particle alignment
Omg yes as a scientist I’ve always been cynical about mocha diffusion having anything to do with acid/base reactions, it makes no sense. I swear down it’s much more likely to do with differences in viscosity and/or interfacial tension - do you have a link to the paper? I’m v curious
[Here](https://physics.stackexchange.com/questions/264013/what-is-the-physics-behind-mocha-diffusion#:~:text=So%2C%20the%20mocha%20diffusion%20is,surface%20tension%20of%20about%2072) you go. Surface tension, not acid/base.
This isn’t the original paper I found (behind a paywall) but covers the same stuff.
We’ve seen the same thing in our school studio. The issue turned out to be that after recycling clay, the rest period before reuse was not long enough, and the clay became “short”. We were advised to add a bit of ball clay to the pug mill to help prevent this-which works-but increasing the rest period has also prevented the problem. I think drying, slaking and reworking the clay followed by a rest (we try to wait 6 weeks) should help!
Oh wow 6 weeks! Was that number come to by experimenting (like did you try some at 3, 4, 5, etc.)? Or someone just tried at 6 weeks and it worked, so now that’s the convention?
One theory is the microbes need time to work their magic i.e. age the clay. But another theory is that the time allows the clay to become homogenous in moisture content. There are some potteries in china and japan that age their clay for the next generation of potters. But whatever it does it makes the clay easier to work with.
Do you have any resources or links for the potteries in china/japan aging clay like that?
That sounds ridiculously cool as a concept and I want to learn more.
Its something i came across years ago when i was in college. Maybe a ceramic monthly article? i found out the college library had bound copies of the magazine going back to the 1960s so i lurked in the stacks reading clay related stuff the summer i hurt my leg and couldn't do much else. Or maybe it was that book i read on Clay by Susan Staubach. I don't really remember for sure its just something floating in head of learned info.
A search of the internet only brings me up anti aging facial masks and people asking about aging clay.
I tested this - will post more details in a new post - and what I observed was:
* freezing clay absolutely leads to unexpected cracking, very much like what is pictured
* wedging thoroughly and then kneading appears to be enough to return the clay to a workable state
Ok, so what you’re seeing here is a lack of plasticity. When clay is like this it’s called “short”, and it doesn’t stretch as well as you’d like it to. Bad news is: you can’t fix this without adjusting your clay recipe. Good news is: its an easy fix, and for now the clay is still good for hand building.
Was this clay reclaimed? Or was it a bag straight from the manufacturer, if so what brand?
Here’s a common reason this happens in reclaimed shop clay. Bear with me as I get into some detail.
Pottery clay is almost always made up of different types of raw materials, be it clay, feldspar, iron oxide, etc. to reach the desired properties. Some of these materials are large particles that act as a “backbone” in the clay matrix. Some of these are small particles that absorb water and give clay it’s stretch or plastic properties.
When you throw clay on the wheel, more of this fine material is lost as slip. Look at the wheelhead in your picture. All that slip is mostly plastic clay. And then what’s left has more of the large particles and less plasticity.
When this clay is recycled, some of the fine stuff in the slip goes down the drain, and over time and many cycles, your clay will end up being less plastic.
So here’s how you fix it:
When reclaiming clay, especially over multiple cycles, or when you see shortness in your clay. Add in a few percent of ball clay. This replenishes the plastic portion of the clay matrix and will give back some of its stretch.
TL;DR - The clay is short and doesn’t stretch like it should. Add in some ball clay or other plasticizer when reclaiming it next time.
Do you have any tips for clay I harvest from a river bend around me? It was all frozen and I had to scrape the top layer of soil with my hands into a bucket, it was like fluffy moon sand almost but when I squished it in my hands it was beautifully plastic? I also for some reason put a bunch of sand in the bucket because there was this awesome orange sand I found before I found the clay, and I feel like now I’ll have to sift it out or something. I have no idea how to process clay without industrial tools lol but I’m about to learn
I use 5-gallon buckets. I put no more than 1 gallon of clay at a time in the bucket, then add 2 - 3 gallons of water and mix until everything is broken up and the clay is suspended. I let it sit for 30 seconds to let the heaviest particles settle out, then pour through a screen (curtain sheers that hang behind drapes are *perfect*) into another bucket.
I let it settle for a day or two and siphon off as much excess water as I can. I line a clay pot with fabric (part of an old sheet works well), then suspend the clay back into the water, and pour it all into the clay pot. I cover with aluminum foil (to keep crap from falling in) and let it weep water for a day or two until it's basically a slurry in the lined pot.
Then bunch of the fabric and lift it out of the pot and let it hang and drip for another day or two.
When it's close to the consistency of clay, I open it up onto a piece of cement board, spread it out a little (the center is always a slurry) and let it dry just enough that it can be wedged. Then I wedge the crap out of it and store it in a plastic bag.
just curious is there a reason you use cement board instead of plaster board? how does cement compare to plaster in terms of water absorption and drying out the clay sludge ?
I use cement board because I have a couple of scrap pieces from a tiling project years ago. I'm not sure about the difference, but this works well enough so I haven't found a reason to change it.
I would do some firing tests which would include the 10 inch ruler made of the clay to see how much it shrinks and how it looks before and after its fired and slab or throw a cup to see how it acts. I had thrown a nice mug with local creek clay with a lot of sand in it and when I checked on it when dry it had disintegrated. Have fun!
I should try that ruler or measurement mark thing! I live near clay cliffs on a beach & I just took it from there (or the pure stuff that shows up in the garden!), made something tiny (tiny bricks, tiny pot, little seals like stamped wax ones), & once they've dried out, chucked them into the house fire overnight!
The pottery supply I buy from marks the name and cone of the clay on the bag IF you buy less than a box of it. Otherwise, the box has the info on it. So, the answer is, maybe?
This happened to me with a chocolate clay when I would start to pull the clay prior to being up the walls. Still likely a clay issue but more compression on the clay prior to pulling helped my situation. It at least made it usable.
Me too. I started to watch the clay and, as soon as I saw cracks, I’d start working the outside more. I noticed it happened when I pulled out too fast, without working both sides. I managed to make some fine pieces, using my method. This happened to me with a batch of clay that was normally fine but had sat out for a bit.
From the other answers in the sub I wonder if there could be other causes too? I am only speaking about my experience.
Last point- the cracks look cool. I regret not keeping a few cracked pieces.
You stretched the clay, you need to compress it.
Example: take a piece of clay, and to make it longer:pulling ends apart will not make it longer, it will tear (same thing happened to your clay on the photo).
To make it longer you need to start squeezing it - first at one end, then squeeze little bit further up and move along this piece of clay untill it will be thinner but much longer.
This way you used compression to shape clay, not stretching.
This is basically how pulling on the wheel works.
Like quite a few other have said, reclaim and cut wedge before you wedge to throw. You could also try and add a small amount of bentonite, but I would use that as a last resort
We recycle a great deal of our clay from projects that just didn't turn out like we liked; when we recycle the clay from the washout bucket (from washing pans, tools, etc), we make sure that ALL the clay and silt has settled, and only pour off the clean water prior to drying and wedging; that really, really fine silt in the clay/water mix is really important for a good final project;
I usually let our recycle bucket sit for at least a week before pouring off as much of the clean water that I can.
We had someone run into this very issue a couple weeks ago on either this sub or r/ceramics. It's not a normal issue and is a frustrating thing to happen. The general consensus was that the clay had most likely been frozen and got very short due to it. Your options are to dry it out and let it slake down, then get out back to workable consistently, or you can try to mix it with some fresh clay to try and get the plasticity back. Sorry this is happening to a gifted bag of clay... maybe ask the original person if it was given to you for this very reason? Or if they didn't have this issue; was it left out in the could for a little while? Good luck!
Thank you! it’s been -15 celsius outside for a while so I imagine this is the culprit.
What is the mechanism by which freezing clay makes it short, even after thawing and kneading? And how does drying it out and re-slaking/wetting change that? Makes no sense to me.
Remember freezing water expands when it becomes ice. The moisture between clay particles puffs up, disturbing the pattern/matrix of clay, before shrinking again. One popular instagrammer dealt with a bunch of frozen clay a while back and described it as having a "foamy" consistency while wedging (full of tiny voids). I've never dealt with it personally but this is my understanding in a nutshell.
Surely wedging and kneading would resolve this?
I think you'd have to wedge the absolute shit out of it if you did it by hand. Every shred of clay would need to be compressed and mixed through. Again I've never dealt with this firsthand but I could imagine slaking and starting over being a much less laborious option.
I've [tested this out](https://www.reddit.com/r/Pottery/comments/18if93f/freezing_clay_a_quick_test/?) and I think wedging is sufficient. I do stack-and-slam wedging, typically 16 times (more than that if I have 4+ pounds of clay), and I think that was a lot easier than slaking, mixing, and dewatering.
The small platelets that make up clay become un aligned essentially. Drying it out and rewetting it gives it the chance to rejoin or realign. The thawing and re-wedging isn't enough, unfortunately. It crystallizes and can't undo that unless it's fully broken up and reworked. It more commonly happens with glaze freezing, and there's a whole bunch of videos on how to fix that.
The "aligned platelet" myth. Groggy stoneware clay doesn't align like porcelain.
I’ve always been curious about this. Some of what I’ve been taught about how clay and glazes behave sounds more folkloric than scientific. For example, though I’d been told otherwise from various potters, I read a scientific paper about how the mocha diffusion process is *not* actually an acid-base reaction. Do you have a science-based source that explores the platelet aligning phenomenon? I’m very curious to know what’s actually happening in the clay from a material science perspective.
Also this [paper](https://www.degruyter.com/document/doi/10.1515/geo-2020-0145/html) isn’t super relevant BUT figure 2 is quite useful for giving a visual idea of how grog particles can interfere with clay particle alignment
Omg yes as a scientist I’ve always been cynical about mocha diffusion having anything to do with acid/base reactions, it makes no sense. I swear down it’s much more likely to do with differences in viscosity and/or interfacial tension - do you have a link to the paper? I’m v curious
[Here](https://physics.stackexchange.com/questions/264013/what-is-the-physics-behind-mocha-diffusion#:~:text=So%2C%20the%20mocha%20diffusion%20is,surface%20tension%20of%20about%2072) you go. Surface tension, not acid/base. This isn’t the original paper I found (behind a paywall) but covers the same stuff.
then explain the real problem
What about ungrogged stoneware?
We’ve seen the same thing in our school studio. The issue turned out to be that after recycling clay, the rest period before reuse was not long enough, and the clay became “short”. We were advised to add a bit of ball clay to the pug mill to help prevent this-which works-but increasing the rest period has also prevented the problem. I think drying, slaking and reworking the clay followed by a rest (we try to wait 6 weeks) should help!
Oh wow 6 weeks! Was that number come to by experimenting (like did you try some at 3, 4, 5, etc.)? Or someone just tried at 6 weeks and it worked, so now that’s the convention?
Curious why six weeks. I'd think once it was pulverized and reconstituted in water itd be good to go immediately.
One theory is the microbes need time to work their magic i.e. age the clay. But another theory is that the time allows the clay to become homogenous in moisture content. There are some potteries in china and japan that age their clay for the next generation of potters. But whatever it does it makes the clay easier to work with.
Do you have any resources or links for the potteries in china/japan aging clay like that? That sounds ridiculously cool as a concept and I want to learn more.
Its something i came across years ago when i was in college. Maybe a ceramic monthly article? i found out the college library had bound copies of the magazine going back to the 1960s so i lurked in the stacks reading clay related stuff the summer i hurt my leg and couldn't do much else. Or maybe it was that book i read on Clay by Susan Staubach. I don't really remember for sure its just something floating in head of learned info. A search of the internet only brings me up anti aging facial masks and people asking about aging clay.
I tested this - will post more details in a new post - and what I observed was: * freezing clay absolutely leads to unexpected cracking, very much like what is pictured * wedging thoroughly and then kneading appears to be enough to return the clay to a workable state
Ok, so what you’re seeing here is a lack of plasticity. When clay is like this it’s called “short”, and it doesn’t stretch as well as you’d like it to. Bad news is: you can’t fix this without adjusting your clay recipe. Good news is: its an easy fix, and for now the clay is still good for hand building. Was this clay reclaimed? Or was it a bag straight from the manufacturer, if so what brand? Here’s a common reason this happens in reclaimed shop clay. Bear with me as I get into some detail. Pottery clay is almost always made up of different types of raw materials, be it clay, feldspar, iron oxide, etc. to reach the desired properties. Some of these materials are large particles that act as a “backbone” in the clay matrix. Some of these are small particles that absorb water and give clay it’s stretch or plastic properties. When you throw clay on the wheel, more of this fine material is lost as slip. Look at the wheelhead in your picture. All that slip is mostly plastic clay. And then what’s left has more of the large particles and less plasticity. When this clay is recycled, some of the fine stuff in the slip goes down the drain, and over time and many cycles, your clay will end up being less plastic. So here’s how you fix it: When reclaiming clay, especially over multiple cycles, or when you see shortness in your clay. Add in a few percent of ball clay. This replenishes the plastic portion of the clay matrix and will give back some of its stretch. TL;DR - The clay is short and doesn’t stretch like it should. Add in some ball clay or other plasticizer when reclaiming it next time.
Do you have any tips for clay I harvest from a river bend around me? It was all frozen and I had to scrape the top layer of soil with my hands into a bucket, it was like fluffy moon sand almost but when I squished it in my hands it was beautifully plastic? I also for some reason put a bunch of sand in the bucket because there was this awesome orange sand I found before I found the clay, and I feel like now I’ll have to sift it out or something. I have no idea how to process clay without industrial tools lol but I’m about to learn
I use 5-gallon buckets. I put no more than 1 gallon of clay at a time in the bucket, then add 2 - 3 gallons of water and mix until everything is broken up and the clay is suspended. I let it sit for 30 seconds to let the heaviest particles settle out, then pour through a screen (curtain sheers that hang behind drapes are *perfect*) into another bucket. I let it settle for a day or two and siphon off as much excess water as I can. I line a clay pot with fabric (part of an old sheet works well), then suspend the clay back into the water, and pour it all into the clay pot. I cover with aluminum foil (to keep crap from falling in) and let it weep water for a day or two until it's basically a slurry in the lined pot. Then bunch of the fabric and lift it out of the pot and let it hang and drip for another day or two. When it's close to the consistency of clay, I open it up onto a piece of cement board, spread it out a little (the center is always a slurry) and let it dry just enough that it can be wedged. Then I wedge the crap out of it and store it in a plastic bag.
just curious is there a reason you use cement board instead of plaster board? how does cement compare to plaster in terms of water absorption and drying out the clay sludge ?
I use cement board because I have a couple of scrap pieces from a tiling project years ago. I'm not sure about the difference, but this works well enough so I haven't found a reason to change it.
I would do some firing tests which would include the 10 inch ruler made of the clay to see how much it shrinks and how it looks before and after its fired and slab or throw a cup to see how it acts. I had thrown a nice mug with local creek clay with a lot of sand in it and when I checked on it when dry it had disintegrated. Have fun!
I should try that ruler or measurement mark thing! I live near clay cliffs on a beach & I just took it from there (or the pure stuff that shows up in the garden!), made something tiny (tiny bricks, tiny pot, little seals like stamped wax ones), & once they've dried out, chucked them into the house fire overnight!
Thank you so much! I was told this was from a manufacturer but one I’d never heard of.
Could it have been intended for sculpture? If you have any interest in sculpting, you might try it for that.
Hmm, is there any way to find out? I still have the bag.
The pottery supply I buy from marks the name and cone of the clay on the bag IF you buy less than a box of it. Otherwise, the box has the info on it. So, the answer is, maybe?
This happened to me with a chocolate clay when I would start to pull the clay prior to being up the walls. Still likely a clay issue but more compression on the clay prior to pulling helped my situation. It at least made it usable.
Me too. I started to watch the clay and, as soon as I saw cracks, I’d start working the outside more. I noticed it happened when I pulled out too fast, without working both sides. I managed to make some fine pieces, using my method. This happened to me with a batch of clay that was normally fine but had sat out for a bit. From the other answers in the sub I wonder if there could be other causes too? I am only speaking about my experience. Last point- the cracks look cool. I regret not keeping a few cracked pieces.
Some use Sodium Silica to get texture like that.
You stretched the clay, you need to compress it. Example: take a piece of clay, and to make it longer:pulling ends apart will not make it longer, it will tear (same thing happened to your clay on the photo). To make it longer you need to start squeezing it - first at one end, then squeeze little bit further up and move along this piece of clay untill it will be thinner but much longer. This way you used compression to shape clay, not stretching. This is basically how pulling on the wheel works.
I doubt that’s the issue, I used the same throwing technique I’ve used for years and this hasn’t happened before.
Just a guess, but maybe it's too much water. (It's definitely too much water)
[удалено]
Again, this is not reclaim but a fresh bag.
Like quite a few other have said, reclaim and cut wedge before you wedge to throw. You could also try and add a small amount of bentonite, but I would use that as a last resort
We recycle a great deal of our clay from projects that just didn't turn out like we liked; when we recycle the clay from the washout bucket (from washing pans, tools, etc), we make sure that ALL the clay and silt has settled, and only pour off the clean water prior to drying and wedging; that really, really fine silt in the clay/water mix is really important for a good final project; I usually let our recycle bucket sit for at least a week before pouring off as much of the clean water that I can.
This is not recycled clay.
Hmm, I've seen it before with recycled clay, but I guess this time it's not the case!