Can you adjust a cone 6 glaze up to cone 10?

[MUSIC] This podcast is a production of the Brickyard Network. To find out more about our lineup of ceramic podcasts, visit BrickyardNetwork.org. [MUSIC] This episode is brought to you by Cornell Studio Supply, located in the gem city of Dayton, Ohio. Find all your pottery and ceramic sculpture equipment and supplies with the best customer service and world-class workshops. Join us for our upcoming Rocket Kale workshop, with Lisa Orr July 18th through the 20th, 2025. Visit CornellStudioSupply.com to sign up. Cornell Studio Supply owned and operated four potters, five potters. >> Hi, I'm Rose, and I'm from the emergency glee system. And we've got your back with our brand new ceramic materials workshop consulting. For just $100, you can get 30 minutes with our team of ceramic superheroes. And we'll help you with fixing your glaze and clay disasters, finding material substitutes, decoding ceramic weirdness. So you name it. Snack your session over at ceramicmaterialsworkshop.com. [MUSIC] >> Hello, my name is Kathy King, and welcome to the Fluxake podcast. I'm coming to you from the Harvard Ceramics program in our fair city, Austin, Massachusetts. I'm here with Rose and Matt Katz of the world-famous ceramic materials workshop. And they are ready to answer your burning questions about clay and glaze. [MUSIC] >> Well, hello, Matt and Rose. >> Hey, Kathy. >> Hey, Kathy. >> It is summer in New England, and since we can't go in the ocean anymore because of the great white sharks, what are you guys doing? [LAUGHTER] >> You can't go to the lake. >> Yeah, head to the lake. >> Well, you know, when you're from New England, as we all are, you know you don't swim in the ocean in New England. >> Yeah, no, it's way too cold. >> It is always cold. I used to always say, because I grew up in New England, Rose grew up in New Jersey. And I used to always say that Rose had spent more time in the ocean than I had in New England. >> I remember as a kid going into the ocean. I love the ocean, but I would come out, I would be like red and purple for seaweed. >> Well, no, just being so cold, like mud. >> Oh, okay. >> My cold temperature, like I wouldn't get out of the water, even though it was so cold, I come out shivering and my lips were blue. >> Well, there's also the fact that in the Northeast, you cannot see through the water. I remember bringing a friend from Florida up to Cape Cod for the first time, and she was horrified that we would ever go in the water that you can't see through. And I'm like, I don't want to see what's on. >> Yeah, no, not to mention the crabs. Yeah, you don't want to see what you're going to step on for. Get that. >> But you were just in warmer environments, Kathy. You did your time in Pendlin? >> Yes, yes. I did a two week workshop at Pendlin School of Crafts in the beautiful mountains of North Carolina. And it is just the most magical place. I mean, I truly consider that I grew up as an artist there. I first went in the 1990s as a work study student, and then went a number of times as a studio assistant, and then ended up, I think this was my maybe six time teaching there. And it's just still as exciting to drive up to that campus as ever. It's all sorts of craft mediums. And I think the super cool part is it's just surrounded by so many artists, and especially potters. I mean, it's like a cavalcade of stars around there. Susie Blinsey and Nick Jorling and Michael Klein and Kurt Anderson just moved and settled down there. And so it's like there's too much to do. So that was a blast. >> You're home away from home. And someday your wife April thought, that's where you moved to. >> Oh, I forgot all about my wife, and we met each other at Pendlin. She was teaching a blacksmithing class in 2012, and I was doing ceramics. And I noticed this very angry looking lesbian at the faculty meeting. And turned out that was her com, the other stair. And it warmed me down, warmed down. >> She hooked it. >> Yeah, all the charm. >> All the time. >> All the boxes are being warmed down, isn't it? >> My goodness. So where are you guys off to? >> We are going to Montana to the Archie Bray Foundation. >> Well, I should say Matt is. I'm just going for fun. >> Oh good, Rose, and are the kids coming? >> Yeah, we're going to go to Yellowstone afterwards. >> That's awesome. >> Yes, he Rose gets all of the luxury because although she's great on the podcast, the Rose is dirty secret as she hates teaching. So I have to do all the live teaching and she just comes along for the vacation. >> Yeah, I get to bring the children on vacation. Oh, low is me. >> I find that's so hard to believe, Rose. >> Really? >> Hey, earlier this year she scored herself a free trip to Scotland just to come along. >> It was nice and it was good because you needed me. >> I did. I did. We had, oh my goodness, that someone that teaches workshops, Katty. I don't know if this scares the heck out of you. But I am always terrified that I'm going to get sick teaching a workshop. >> Oh, sure. >> And because you travel all this way and people travel all this way. And it never happened to me even after COVID, I never got sick. And then when I was in Scotland, I got food poisoning. And I was down for 24 hours. And luckily enough Rose was there and no matter how much she hates teaching, she stepped in and did a day for me. It was amazing. >> I did. >> She was so- >> I undid all the good stuff he did. >> [LAUGH] >> Well, I'm always asking you to bring me on these trips so I can carry the bags or something. And if I had had a pitch hit on teaching a glazed chemistry class, that would have been interesting. [LAUGH] >> Why is this glazed doing this, Katty? And like, I don't know. >> No, no, no, no. >> [LAUGH] >> Listen to the podcast. >> [LAUGH] >> Awesome. >> All right, so we have so many questions to get to today. So let us jump right in, the water is fine. And we will start with a question from Nick from North Carolina. So I was just talking about converting mid-fire recipes. >> Hey, for fluxic, this is Nick from North Carolina. Care is about how you go about converting mid-fire recipes to high fire. I am interested in trying some cone sick six recipes that rely on the Bristol reaction, but not sure exactly how to adjust for those going to come in. And any info you could share would be great. Thanks so much. >> Well, speaking the music of my heart, not trying to take 10 down to six, taking six up. >> I'm going to take a break while you answer this. >> Please, still hold on. Nick, she's, sorry, are you, are you associated or are you single? Because I don't know on plan love. >> I think this is a plan. Unfortunately, I can't have that. It's because Nick picked the one situation where it's a little bit more difficult to do that. So when we're talking about glazes, right? One of the things you hear me say all the time is we're not firing to a temperature. We are firing to the completion of the chemical reaction. And that chemical reaction happens within a general temperature range. And that's what classifies as high temperature. Even cone 10 is not even so much a specific thing. It's a general temperature range where chemical reactions are done. And the same thing with cone six. And the thing with glazes and temperature in chemistry is no matter how much people don't want to believe it, all chemistry is based in cone 10. Cone 10 is the basis and everything else is a derivation from cone 10. And it's a question of how you're getting that temperature down. Nine times out of 10, when we're talking about mid temperature cone six, the answer is boron. And boron is a glassformer like silica that functions at a lower temperature. And so it just drags the entire system around along with it. And it's super easy to convert a glaze that is cone six because of boron two cone 10. I literally opened up a kiln this morning for I'm working on a project for our friend Kevin and Kevin's been working at cone six and he just got a cone 10 reduction kiln. And he said, I love this glaze at cone six, but can we make it a cone 10 glaze? And I said no problem. It was-- Pretty much just take the chemistry of the glaze of cone six, remove the boron, and then just make sure everything was the same. So you get the same alkaline fluxes, alkaline metal fluxes, the silica aluminum. You basically match them, and it just works at content, because boron just makes content glazes work at cone six when you have the right amount of boron. So you do it in reverse. You just take out the boron, and then it'll work at content. And sometimes it takes a little bit of nudging back and forth. Like you take the silica up and down, because it might not be dead on the same, but it works pretty close. And literally this kill mode, I just unloaded this morning, and it was pretty much dead on what I was hoping to see of that six glaze now works at 10 in reductions. That's good. The problem that Nick is going to have is he mentioned that he's got this Bristol Glaze reaction. And Bristol Glazes are the other major way that we bring temperatures down to cone six. So Bristol Glazes occur with this special chemical reaction called a eutectic that happens between calcium and zinc very specifically. And that will bring your temperature down to about cone six. And the problem is that Bristol Glaze reactions are not really all that negotiable with temperature. So they kind of only work at cone six. And if you want to go higher, what's going to happen is that the glaze is still going to be slightly overfluxed. And there's not a ton that you can do about it. Now it depends on how nimble Nick is with the overall chemistry, because I'll give you a few options, but it's not just sort of like a change one thing in the recipe and hope it works. It's a real systemic chemical problem. So the couple of things that you really need to look at for this as a conversion is one, you need to look at the exact proportion of zinc to calcium, because you can't get rid of one or the other because the colors and the textures that you're getting from this glaze are dependent on those alkaline refluxes, the zinc and the magnesium. So you can't just eliminate like calcium and go like, yeah, it's just going to be a zinc basically, no, no, no, you got to have both of them. But if you can move the chemistry between the zinc and the calcium so that one of them becomes more dominant, you might be able to move out of the Bristol glaze reaction and still have the two of them, because to go real nerdy for a Bristol reaction, you need both zinc and calcium to be over point two and under point five via UMF. Kathy's eyes just rolled so hard. I heard the Queen. It's like, is it over yet? It's so painful. Oh, I'm not even. I know you're just getting revved up. I got it. I'm not going to have to keep for a day for it's end. And then the other thing you could do is you can try to bring up your silicone aluminum levels a little bit. I'd aim to keep the silicone aluminum ratio the same, but you want to bring the levels up probably about point two. That's not a great solution because once again, it can change the overall chemistry of the way the system's working. And like I said, both of these are sort of hoping it sort of backs off of the Bristol glaze reaction, but both of those might sort of break the nature of the glaze because oftentimes with glazes, the chemistry we have are very, very specific and they don't have a ton of wiggle room. And so this may be a case where it's really, really tough. But yeah, if you didn't have a Bristol super easy, just get rid of the boron match the overall chemistry. But when you do have a Bristol might be a little bit hard. But yeah, try look at the zinc to calcium ratio and then look at the, look at the silicone aluminum levels and those, those might help you. That wasn't so painful. I don't know. Kathy is asleep. No. Well, I remember like the beginnings of my experience with glaze chemistry was when everyone was trying to go from 10 to 6. And basically the answer was, okay, you've got to break it down each material into its formula and move some moles around or something like that. It had to do something with moles, I think. Oh, yeah, yeah. Yeah, yeah. Yeah, yeah. You do it long way. Yeah. Right. Somehow you would get it down to a cone six. I'm not sure if that was accurate or not. Mine was always wrong when I did that. Yeah. Well, the worst part is that back then the numbers were kind of made up, which is really hard. One of the things that we really advocate is that there's this model out there called Stull, which gives us all the chemical parameters that glaze will happen. But when we were all students, they use this system called limits and limits were literally just like a list of numbers. And they would be like, these are good numbers and these are bad numbers. And the thing about limits is that they're total garbage. They are completely made up. And you can tell because every single book out there will just have different numbers. Why? Because they want to. That's why. And I know there are still people out there that advocate limits, but move on man, the limits are over. That's the past. Let's get with the future. Let it go, man. Just let it go. Because yeah, I mean, I can literally, I have a great slide in my teaching where like I pull up limits from three different books and they literally contradict each other. You know, oh, yeah, it's fantastic. And it's because they're just made up. But it's like the, the Ned Flanders and the Simpsons. Like, I, you know, I, I followed all the rules. I did the things that even contradicted the other things. Like it, it was a coping mechanism more than anything because they didn't have like stole, which is this visual model to see what, you know, these, these chemical chains are going to do. But yeah, it was learning glazed chemistry was painful when we were young. Like that's the thing that Rosemary really trying to get people past. That's like, there are so many better ways to do it. But yeah, you still have to understand the chemistry. I'll drag you with this. Cassie, will you like it or not? Well, Matt, okay, well, we're going to go with it then. So today's Matt's special special day. And I have another question that is round Cone 10. And this question comes from Amy from New Zealand and Amy wants to know about taking her kiln to Cone 10. Hi, Matt. Kathy and Rose. This is Amy calling in from New Zealand. My question today is about kilns and clay and firing to Cone 6 versus Cone 10. And mostly make functional pieces such as mugs and fire them to Cone 6 oxidation in my electric kiln at home. As I've been listening to your podcast and learning about the importance of vitrification, I've become increasingly concerned about my decision to fire to Cone 6. I'm having trouble finding a Cone 6 clay body that actually vitrifies it Cone 6, which is leading me to consider the idea of giving up on Cone 6 clay entirely and just firing to Cone 10 instead. While in theory, my kiln claims to be able to go to Cone 10, after listening to your podcast, especially the kiln episodes with Matt and Freddie, I'm suspicious that my kiln is going to hate me for making it go to Cone 10. So after all that, my question is basically this and it has three parts. So the first part is how do you know if your kiln is actually built to perform at Cone 10? What are some practical things to look for test or measure? The second part is if your kiln, if you find it's not actually built to perform at Cone 10, how do you go about identifying a kiln that is built to go to Cone 10? And then the final part is if you did then in the long term work towards financing a kiln built for Cone 10, could you potentially prolong its life by exclusively using it as a glaze kiln and the old kiln as a bisque kiln? Anyway, thank you so much for listening to me, Randall, and I really hope you're my bill to help. Thank you. Do you see what you've done, Matt? This poor child, a new seal in questioning every part of her clay making journey because of the genius plan is coming to fruition. She was perfectly happy. Amy is also a student. Oh, all right. So she's drank the cool later. I got it. I got it. She's good. All right. Well, that was a 17-part question. So take any part of that. Well, the first off, I'm pretty sure that all our kilns eat that. So I like them back. And it clarifies this is electric we're talking about. Yeah. Yeah. Great. So the gas kilns have to be built big just for the way like convection currents work and combustion. And so, and you can build a gas kiln that goes to cones, you can fire gas kiln to cone six, but they all have to be cone 10 sort of by default. Like even with our kiln, we tried to get the smallest kiln that they would make. And it's still 12 cubic feet of stacking space. It's still huge. So that's always the thing. So yeah, electric kilns. Yeah, I do love this question. And the real simple version is is everything of the highest quality possible. And that's really where you have to start asking questions about exactly what is in the kiln. The number one thing I like to point at. when we're talking about kiln construction is the bricks. Now, again, being in New Zealand, there may be a different brick standard. I can only talk about the American brick standard. But bricks are sold via the temperature that they are functional at. And here in the states, the two most common types of bricks that kilns are made out of, they're all head of this type of brick. We call it a soft brick. But that soft bricks are generally sold as K23s or K26s, then that you can't get other ones with those of the ones. Yeah, you can get other ones, but they're not. They're a little harder to find. Yeah. So K23, the 23 in there is 2300 degrees Fahrenheit, which is the peak temperature for that brick, which is roughly cone eight. And K26s are 2600 Fahrenheit, which is roughly cone 14, if I remember my fakenite numbers off the top of my head. So guess what everybody? The K23 bricks are cheaper. The last time I looked them up, they were like a dollar 50, a brick cheaper than the K26s. And so those are generally what are used in kiln building is K23 bricks. But you remember how I said that they're only rated to cone eight, and that inherently becomes the problem. Because when you are firing those bricks to a temperature above their rating, two things happen. The A number one problem is that they do not retain heat very well. And the thing I will always say is that kilns are not boxes for generating heat as much as they are boxes for retaining heat. They have to keep the heat in. And if you are firing them past their working range, they do not keep the heat in. And that's a huge, huge problem, because can you take that kiln to cone 10? Sure you can. The problem is you have to put in heat to climb in temperature. But if you're losing heat, 'cause the walls don't hold it in, you have to put in heat to retain the heat that you already had, and then put even more in to build heat. And this is why oftentimes people are like, "Oh man, I don't fire to cone 10 because cone six is so much more fuel efficient and cone 10 uses so much more energy." That is completely untrue. We've actually measured this in our kilns built for cone 10. Cone 10 is 5% hotter than cone six, and art kilns only use 7% more energy to get to cone 10. Okay? Now the problem, my lowest people believe that is because they're using a brick that is not heat rated for cone 10, versus art kilns are using the 2600 bricks that are heat rated for cone 10. And so it keeps that heat in. But if your bricks are only rated for lower temperature, you're just gonna have to spend more energy to get to the higher temperature, 'cause you're dumping more heat through the walls that you wanna be keeping in. And it just becomes a vicious cycle. And so like in that case, like do you use a lot more heat? Sure you do. But if you use the K26 bricks, it'll hold the heat just fine. The other problem that happens when you over fire your bricks is that they will tend to shrink and check and crack on the inside. And so you'll start to see your bricks getting all funky if you over fire them. And that's not good for the long-term life of your kiln. And it basically goes to every single part of the kiln that you want the elements to be the thickest gauge, highest stating them out of bat. And I remember what the elements are. And the thermal couples, right? You always hear me say if you want the S-type thermal couples for reading temperatures accurately. And that's a big deal for cone 10, right? Cone or S-type thermal couples are good to 1600 C. And K-type thermal couples are only good to cone five, which is like 11 as 76. C. And so it's just all of those things in combination. So like what I always say when I'm talking to people of like when they're trying to buy a kiln, all those things that are sold as optional extras are the things that you actually need. Like the upgraded thermal couple and the upgraded elements and all of that. And like, that is what is going to get you a better performance. And that is just what it is. But if you do have the kiln built for a better performance, getting to cone 10 is no problem. It's really easy. But it's always going to be the sacrifice of it's going to be bigger and it's going to cost more money. And that's always the question you have to deal with. And don't go by Matt's estimates of cost for brick because he's way off. Good to know, right? Go for old over. Thank you. Does it have anything to do with your electricity? Unlike what your house can take or your home studio can take? No, most electrical efficiency has a couple of factors that could be better for doing these things. But so-- Kathy asked the nerd question, man. Now I got to answer it. I know. The thing to understand about the electricity is most homes-- again, I'm only speaking that in states. I can't speak for everybody. But most homes in the US will have a 200 amp service at 240 volts. And that's fine to run a kiln. That is a less efficient form of electricity that you will find industrially. So industrially, you'll often-- oh, I should say-- the domestic is also what we call single phase power. Industrial power is often 3 phase power at 240 or 208, which gets weird. And then it can be up to 480 volts. And that is more efficient if you can get 3 phase power at the higher voltage or the higher amperage. But people don't really have that. In our studio, we have domestic power. So we've got single phase, 243 volts. We have 200 amps running to our studio. And we could fire all of our kilns on that. But if you're just in-- if it's just part of your house, it's like having another closed dryer. It's basically similar amperage and voltage to a closed dryer for your kiln. So it's not that-- or actually ovens tend to draw more electricity. So it's not that bad. Like you totally can get those for your home. That's not the issue. It's just a question of how well built they are. And then the other thing is this design is a big deal. So we talked about the type of bricks. The other thing is how thick those bricks are. Most kilns in the states are made with a 2 1/2 inch thickness of brick, which is not particularly thick. Like I can tell you, I've literally just measured it. Our gas kiln's walls are 10 1/4 inches thick. So they are four times thicker than most electric kilns. And so you get the better bricks and the thicker walls. It just holds the heat in. Those thin walls, they just radiate heat out so fast. And like I said, it's really about keeping that electricity in. And that really becomes the harder decision. From a quality of work standpoint, that's where Amy is right on is that the work is going to be better. It's easy to find clays that are going to be vitrified. Glazed chemistry is going to be easier and cheaper, all that type of stuff. The only real things I would say, the one advantage that cone 6 has is if you use things with a lot of stains, stains are more stable at cone 6, which you've talked about before. But if you're just using oxides, it doesn't make a good difference. They both basically perform the same at either temperature. But it is definitely looking at those metrics of the best that you can find. I mean, I don't know what the kiln suppliers in New Zealand are. But I mean, the Aussie kilns, when we were down there, were all pretty high quality. So I wouldn't be too shocked. And there's different quality makers here in the states that are making some thicker kilns and some better kilns. We know we were at in Sikinat, too long ago, in Rota, who is a German kiln manufacturer, has announced that they're coming to the states. And they had a pretty sweet looking kiln. Those walls were-- Those walls were thick. Yeah. Yeah, baby. Is it Rota or is it Rhodes? Rota. Rota. And I was very interested in with them. I introduced myself and we'd been emailing back and forth since Ensika. And it's interesting. I'll be faster to see. Are you jealous, Rose? We don't need another kiln. [LAUGHTER] We don't have room for another kiln, right? I mean, did you know about Matt and Rota? I mean, yes. He's very open and honest, but we don't need another kiln. I didn't tell the other kilns I was seeing someone on the side. Yes, I mean, really, don't tell the blouse. You know, Matt, the bigger problem is, Freddie was right there at Ensika. And I saw him looking around the corner being like, we talk another kiln builder's portion. I know. I know. Oh, the drama, the intrigue, tell you what. And then the other big thing was one of the manufacturers came out with a small electric kiln that goes into a regular household current. And I don't know much about that. But I saw a lot of people like, woo, OK. I don't have to get the special electricity. I'm like, I don't know how hot it goes, but or how long the firing is. Let me tell you, that doesn't work very well. OK. We know. know some people that have bought them and their advertisers being co-entend, but yeah, that they work on a 120 circuit. Yeah, they're going to, they can't pull enough juice is the problem. And so like, it's a great marketing exercise. And like technically, could it do it? Yeah, but, but you know, that's the same way that we're just talking about like the industrial electricity is more efficient. 240 is more efficient and it'll build the heat and hold the heat better because of that extra power. And the 110, we've had a bunch of students try them and try them versus a 240 test kiln. And I, I don't think I could say that they're worth it, especially for hired. Like if you're working at Kono for, if you're doing China painting or decals, sure, that it'd be okay. But if you're actually trying to get to like, vitrification temperatures like six and ten, I don't know if I'd do that one. Well, bumps get me out again. No, no, I mean, I'm sure I just think a lot of people will run out and get those. And you know, just for the ease of it. But, and do you research people? Do you research? All right, you two. That is all the time we have for today. So many more questions to answer. So we look forward to all of you joining us next time. Till then, Matt and Rose. Bye-bye. Thank you, Kathy. Well folks, that's it for this week's episode of For Flux Sake. I'd like to thank the listeners who submitted questions this week. And if you want your question answered on the show, shoot us an email at for [email protected]. So join us next time and win in your studio. Remember what Rose always says. Always remember to test test test. This is a test of the emergency glazed system.