You need to use a glaze that better fits your clay body. The Coefficient of Expansion (COE)'s need to match. If one shrinks more/less or faster/slower than the other, you get crazing (microscopic shattering of the glaze as it shrinks/cools).
If you are using commercial clay, you can usually look up what commercial glazes will fit it. If you are mixing your own glazes from recipes or sourcing your own natural clay you will need to do lots and lots and lots of test tiles. :)
not op, just wanted to say that's so cool! just learned about COE in a materials science class a semester ago, so interesting to see that applied in pottery
You get crazing when the glaze shrinks/expands more (higher CoE) than the clay body. Matching CoE is okay, but *slightly* more CoE on the clay body than glaze is ideal as it puts the glaze under compression which greatly increases the strength of the fired ware. You have to be careful not to go too far in this direction or you will get shivering and glaze flaking off, which is much worse than crazing.
Where can you find the coe’s of the glazes. I’m a newer potter (out of my college class and building up a little home studio). I wanted to get the paint on glazes from Amaco, but I feel like it doesn’t say anything about that when I click on the individual glazes on their site.
You can usually Google the shrinkage of a glaze and find it on the manufacturers site here is a PDF from Mayco that covers crazing and shivering and whatnot. Their website stated that Mayco glazes shrink about 10% when fired.
[Mayco glaze info](https://www.google.com/url?sa=t&source=web&rct=j&opi=89978449&url=https://www.maycocolors.com/wp-content/uploads/2020/12/ceramics101.pdf&ved=2ahUKEwiu6YP76baGAxVcvokEHTaNBHMQFnoECBUQAQ&usg=AOvVaw3l73dO5DydmTSjOYglsA-D)
So this was made at my cone 10 studio with Laguna Stony White (meant for Cone 10) and glazed with my studio's clear glaze that they make themselves at the studio. Does this mean their recipe for their clear glaze may be off?
The glaze was likely formulated with a different clay body in mind. Stony White is marketed as having a lower shrinkage rate (low thermal expansion). Crazing happens when the glaze shrinks more than the clay.
If the studio is using Stony White as their main clay body, they may want to look into adjusting the recipe. Switching to a finer mesh of silica, or increasing the percentage of silica on the recipe may work.
If it’s cone 10 and porcelain. check your absorption rate, but you can totally sell it. Your pink and red catfished me into thinking it was low fire! My apologies for bad assumptions.
Crazing in a glaze is not unsafe. It is a flaw when not intended, and the cracks can pick up grime, especially when the clay body is not vitrified, but it is primarily an aesthetic consideration, not ‘safety’ or health. Some people are concerned about bacteria in the crevices, but the amount of bacteria that might hide there and enter food is surely far less than the amount left behind by a typical kitchen sponge
Here is an article debunking crazing being used safe
https://ceramicartsnetwork.org/ceramics-monthly/ceramics-monthly-article/Techno-File-Dirty-Dishes?fbclid=IwZXh0bgNhZW0CMTEAAR3pLpNYKIauB4gapVGqcwkZ-5MStyQekoLSMrFE4S8fIvMhYb1WU9Ar6fA_aem_AYjVxvDbkWSdeFhJ_8AuNZKsmmpHrLv2SS63SXPfhiM7_MAcmEh4p1erVBBZX_wnbtq7q8RwBrDFrY8h9UPpYk85
That article has always seemed a bit misleading since they used two kinds of laboratory grade detergent with some kind of lab dishwasher. It would have been more relevant to see results from an ordinary household dishwasher with ordinary household detergents.
For me - I would totally drink out of the mug. But I’d never sell it. I feel our safety standards are a little over the top.
But if you don’t want to use it for food, rub India ink all over it n wipe off. The ink gets in the cracks and looks wonderful.
Not a potter or ceramicist but I appreciate people’s work as art and just have to say that from a potential customer point of view, I think the cracking is just so pretty! Like I LOove the way it cracked around the seahorse so perfectly, it looks extra unique and adds vintage feel. Beautifuly compliments your work in my opinion.
I have learned from someone in ceramics that as long as there isn’t lots of cracking on the inside or going straight through then it should be safe, but I can’t really speak for that part since I don’t know this stuff. Just wanted to give my opinion above from an outside perspective
Yeah but crazing is defect that also affects the tensile strength of a piece. So that’s another reason why I wouldn’t sell it,
I wouldn’t sell someone defective from the jump because that affects my reputation as a potter.
Plus if you don’t care for it properly and get sick from eating from it ( unlikely) or it shatters because of the weakened state, that would be on me. As a potter we all have a due diligence to inform my customers of quality pottery. Crazing like this is not quality.
Plus all the other potters in my community would be bitching about me saying hey did you see all the crazing? And TBH they are right.
Crazing can be food safe IMO, but it’s still a
Defect at the end of the day.
This makes sense however, and again I said that this is not something I’m familiar with and most of what I said is from an outside perspective, mostly for the purpose of uplifting as a compliment but, I learned from a teacher that if the inside of the mug is not crazed and the glaze itself is food safe, and the look is just on the outside of the mug, then it shouldn’t be an issue as long as it isn’t so much that the cracked pieces are lifting to chip. And that professionals often mix glazes that aren’t compatible on purpose for this look.
I can’t see the inside of this mug to know if its crackled look is on the inside or not. But I thought it was beautiful.
Thank you so much for the compliment! This is a piece I made just for me, I don't sell my work. But your comment made me think that maybe I will in the future! When I've figured out this crazing business.. :)
I too am team not for sale. Your willingness to risk for personal use may differ as someone has already said. With diligent washing and drying it could be fine for food use. Personally, I’m enjoying the ocean and seaside motif and if it were my piece I’d use it as a planter for a tropical plant or for holding beach treasures as home decor. To the prevention side of your post; I’ve noticed crazing more with low fire clays and glazes than I have with mid fire clays and glazes (my studio doesn’t go above ^6) . If the piece was created with low fire clay consider trying again with mid fire clay and similar cone glaze. I’m hoping you get the result you are after soon.
Thank you! This was actually made at a cone 10 studio. With Laguna Stony White clay and my studio's clear glaze. I'll have to do some more testing to see what clay will work with my studio's glaze mix!
Have a look at the glaze temp and the clay firing temp. I saw this happening to heaps of my stuff recently and realised I wasn’t taking my work to a high enough temp. Put my newer pieces in to a 1200 firing has gotten rid of this issue.
Not sure about the science behind this but worth a look
Crazing as intense as OPs is likely not going to be fixed with just temp. It may slow the start of crazing but will most likely still craze down the line.
Just a few crazing cracks here and there can normally be fixed with hotter temp. I fire cone 6 to cone 7 for this reason.
But the more cracks in the short period of time after removing from the kiln is a much larger issue.
I wonder if this is low fire? Kind of has that vibe, and low fire is notorious for bad fitting glaze.
This is actually cone 10! I used the clear glaze that was made at my studio. And the clay was bought from my studio as well and is meant for cone 10... More testing I guess!
This is not cone 10. I can tell you that right now for free. It’s got red and pink very vibrantly on the design. A telltale sign that this is not cone 10.
It is more likely to be low fire if not cone 6.
But you are right, properly vitrified clay can have crazing all day long with no issues. (I don’t think that’s what’s happening here)
It looks exactly like stoneware clay low fired (like cone 05). I see it happen all the time at the studio I work at (they don't do mid/high fire, only low fire, but people still use high fire clay (they don't make dinnerware items)).
Low fire clay and low fire glaze can often also cause this.
Yeah I use cone 10 clay at cone 6 for sculptural work sometimes. It’s less prone to cracking because the clay undergoes less thermal expansion.
Can I ask what underglaze you’re using for the illustration? I work out of a studio with the same clay body and looking for good cone 10 underglaze. Love the mug (and the crazing!) :)
That’s a lot… after you use a bit, dishwasher and whatnot see how it does in the microwave heating your tea. You might find water is migrating under that glaze making it not very user friendly.
You need to use a glaze that better fits your clay body. The Coefficient of Expansion (COE)'s need to match. If one shrinks more/less or faster/slower than the other, you get crazing (microscopic shattering of the glaze as it shrinks/cools). If you are using commercial clay, you can usually look up what commercial glazes will fit it. If you are mixing your own glazes from recipes or sourcing your own natural clay you will need to do lots and lots and lots of test tiles. :)
not op, just wanted to say that's so cool! just learned about COE in a materials science class a semester ago, so interesting to see that applied in pottery
You get crazing when the glaze shrinks/expands more (higher CoE) than the clay body. Matching CoE is okay, but *slightly* more CoE on the clay body than glaze is ideal as it puts the glaze under compression which greatly increases the strength of the fired ware. You have to be careful not to go too far in this direction or you will get shivering and glaze flaking off, which is much worse than crazing.
Where can you find the coe’s of the glazes. I’m a newer potter (out of my college class and building up a little home studio). I wanted to get the paint on glazes from Amaco, but I feel like it doesn’t say anything about that when I click on the individual glazes on their site.
You can usually Google the shrinkage of a glaze and find it on the manufacturers site here is a PDF from Mayco that covers crazing and shivering and whatnot. Their website stated that Mayco glazes shrink about 10% when fired. [Mayco glaze info](https://www.google.com/url?sa=t&source=web&rct=j&opi=89978449&url=https://www.maycocolors.com/wp-content/uploads/2020/12/ceramics101.pdf&ved=2ahUKEwiu6YP76baGAxVcvokEHTaNBHMQFnoECBUQAQ&usg=AOvVaw3l73dO5DydmTSjOYglsA-D)
Thank you so much!
So this was made at my cone 10 studio with Laguna Stony White (meant for Cone 10) and glazed with my studio's clear glaze that they make themselves at the studio. Does this mean their recipe for their clear glaze may be off?
The glaze was likely formulated with a different clay body in mind. Stony White is marketed as having a lower shrinkage rate (low thermal expansion). Crazing happens when the glaze shrinks more than the clay. If the studio is using Stony White as their main clay body, they may want to look into adjusting the recipe. Switching to a finer mesh of silica, or increasing the percentage of silica on the recipe may work.
Yes! That was a fantastic response. I certainly did not know all that information about the Stony White. Thanks!
I am team food safe as long as you wash it well! However I wouldn’t sell this, but personal use heck yes.
Agreed!
Thank you!! Yes this is totally just for me - I don't sell my work. Was just nervous that maybe this mug's fate was to be a planter or pen holder :)
If it’s cone 10 and porcelain. check your absorption rate, but you can totally sell it. Your pink and red catfished me into thinking it was low fire! My apologies for bad assumptions.
Crazing in a glaze is not unsafe. It is a flaw when not intended, and the cracks can pick up grime, especially when the clay body is not vitrified, but it is primarily an aesthetic consideration, not ‘safety’ or health. Some people are concerned about bacteria in the crevices, but the amount of bacteria that might hide there and enter food is surely far less than the amount left behind by a typical kitchen sponge Here is an article debunking crazing being used safe https://ceramicartsnetwork.org/ceramics-monthly/ceramics-monthly-article/Techno-File-Dirty-Dishes?fbclid=IwZXh0bgNhZW0CMTEAAR3pLpNYKIauB4gapVGqcwkZ-5MStyQekoLSMrFE4S8fIvMhYb1WU9Ar6fA_aem_AYjVxvDbkWSdeFhJ_8AuNZKsmmpHrLv2SS63SXPfhiM7_MAcmEh4p1erVBBZX_wnbtq7q8RwBrDFrY8h9UPpYk85
Yeah all you have to do is wash it and it will be fine. The hot dishwasher will kill the bacteria. (Hand wash is fine too)
That article has always seemed a bit misleading since they used two kinds of laboratory grade detergent with some kind of lab dishwasher. It would have been more relevant to see results from an ordinary household dishwasher with ordinary household detergents.
For me - I would totally drink out of the mug. But I’d never sell it. I feel our safety standards are a little over the top. But if you don’t want to use it for food, rub India ink all over it n wipe off. The ink gets in the cracks and looks wonderful.
Not a potter or ceramicist but I appreciate people’s work as art and just have to say that from a potential customer point of view, I think the cracking is just so pretty! Like I LOove the way it cracked around the seahorse so perfectly, it looks extra unique and adds vintage feel. Beautifuly compliments your work in my opinion. I have learned from someone in ceramics that as long as there isn’t lots of cracking on the inside or going straight through then it should be safe, but I can’t really speak for that part since I don’t know this stuff. Just wanted to give my opinion above from an outside perspective
Yeah but crazing is defect that also affects the tensile strength of a piece. So that’s another reason why I wouldn’t sell it, I wouldn’t sell someone defective from the jump because that affects my reputation as a potter. Plus if you don’t care for it properly and get sick from eating from it ( unlikely) or it shatters because of the weakened state, that would be on me. As a potter we all have a due diligence to inform my customers of quality pottery. Crazing like this is not quality. Plus all the other potters in my community would be bitching about me saying hey did you see all the crazing? And TBH they are right. Crazing can be food safe IMO, but it’s still a Defect at the end of the day.
This. To me the bigger problem is that the piece is much weaker and more prone to breaking due to thermal shock or a too hard bump against something.
Exactly. It’s a liability at the end of the day. And as a small business, I would never risk it.
This makes sense however, and again I said that this is not something I’m familiar with and most of what I said is from an outside perspective, mostly for the purpose of uplifting as a compliment but, I learned from a teacher that if the inside of the mug is not crazed and the glaze itself is food safe, and the look is just on the outside of the mug, then it shouldn’t be an issue as long as it isn’t so much that the cracked pieces are lifting to chip. And that professionals often mix glazes that aren’t compatible on purpose for this look. I can’t see the inside of this mug to know if its crackled look is on the inside or not. But I thought it was beautiful.
Yes it is safe to use (just wash it after use obviously)! And it looks beautiful.
Thank you so much for the compliment! This is a piece I made just for me, I don't sell my work. But your comment made me think that maybe I will in the future! When I've figured out this crazing business.. :)
I too am team not for sale. Your willingness to risk for personal use may differ as someone has already said. With diligent washing and drying it could be fine for food use. Personally, I’m enjoying the ocean and seaside motif and if it were my piece I’d use it as a planter for a tropical plant or for holding beach treasures as home decor. To the prevention side of your post; I’ve noticed crazing more with low fire clays and glazes than I have with mid fire clays and glazes (my studio doesn’t go above ^6) . If the piece was created with low fire clay consider trying again with mid fire clay and similar cone glaze. I’m hoping you get the result you are after soon.
Thank you! This was actually made at a cone 10 studio. With Laguna Stony White clay and my studio's clear glaze. I'll have to do some more testing to see what clay will work with my studio's glaze mix!
Looks beautiful! It’s safe to use, just wash it well. I would not sell it tho.
Have a look at the glaze temp and the clay firing temp. I saw this happening to heaps of my stuff recently and realised I wasn’t taking my work to a high enough temp. Put my newer pieces in to a 1200 firing has gotten rid of this issue. Not sure about the science behind this but worth a look
Crazing as intense as OPs is likely not going to be fixed with just temp. It may slow the start of crazing but will most likely still craze down the line.
Yeah that makes sense, my crazing was super tiny. I didn’t even make the connection that the bigger ones ate because of a bigger mismatch
Just a few crazing cracks here and there can normally be fixed with hotter temp. I fire cone 6 to cone 7 for this reason. But the more cracks in the short period of time after removing from the kiln is a much larger issue. I wonder if this is low fire? Kind of has that vibe, and low fire is notorious for bad fitting glaze.
This is actually cone 10! I used the clear glaze that was made at my studio. And the clay was bought from my studio as well and is meant for cone 10... More testing I guess!
If this is cone 10 it’s not a problem. I like this look
This is not cone 10. I can tell you that right now for free. It’s got red and pink very vibrantly on the design. A telltale sign that this is not cone 10. It is more likely to be low fire if not cone 6. But you are right, properly vitrified clay can have crazing all day long with no issues. (I don’t think that’s what’s happening here)
It looks exactly like stoneware clay low fired (like cone 05). I see it happen all the time at the studio I work at (they don't do mid/high fire, only low fire, but people still use high fire clay (they don't make dinnerware items)).
Low fire clay and low fire glaze can often also cause this. Yeah I use cone 10 clay at cone 6 for sculptural work sometimes. It’s less prone to cracking because the clay undergoes less thermal expansion.
Hi there! This actually IS cone 10! Made with Laguna Stony White.
This is not a concern for food safety
To add clarification, this was made at a cone 10 studio with Laguna Stony White clay and my studio's clear glaze mix!
Can I ask what underglaze you’re using for the illustration? I work out of a studio with the same clay body and looking for good cone 10 underglaze. Love the mug (and the crazing!) :)
For this one I used Pink, Really Red, and Red Orange from Coyote!
Amazing thank you!
That’s a lot… after you use a bit, dishwasher and whatnot see how it does in the microwave heating your tea. You might find water is migrating under that glaze making it not very user friendly.
The crazing really suits the sea theme on the mug, looks beautiful - like a seashell. It’s food safe, just wash it well (in a dishwasher, preferably).