14: Glaze Doctors - For Flux Sake Live!

0:00Welcome to NSEKA 360, a podcast that amplifies and uplifts the voices of the ceramic community. I'm Edith Garcia for the National Council on Education for the Ceramic Arts. Visit nseka.net to learn more about how membership cultivates a clay community and shapes content and opportunities for the field. Follow us on Instagram and Facebook for the latest information about NSEKA.

0:30Hello, this is Amitra Sinha. I am an NSEKA board member, and I'm happy to introduce this week's NSEKA 360 podcast. This episode features the conversation about glaze development and troubleshooting with Kathy King, Matt Katz, and Rose Katz. I invite you to listen as our panel of experts, answers questions in this fired-up live recording of the For Flux Sake podcast

1:07that happened in person at the 2024 NSEKA Coalitions Conference in Richmond, Virginia. Special thanks to the Brickyard Network for co-producing this episode and supporting podcasting in the ceramics community. Registration is now open for our 2025 Salt Lake City Conference. Please check out the NSEKA website to register. If you enjoy this podcast, please support NSEKA's programming by donating at

1:38nseka.net slash donate.

1:47All right. Hello. Welcome, everybody. Welcome. Hi, everybody. So welcome to the For Flux Sake takeover of NSEKA's traditional glaze doctors. I am here with the lovely Rose Katz and Lord Celsius himself. So how was your trip getting you?

2:19Interesting. It was interesting. We had a family commitment and so we landed at 1 30 a.m. last night. So we're bright-eyed and bushy-tailed. Yeah. As always, right? Yeah. Just for an hour. That's all you need to do is for an hour. We're going to crash before we get off the last step of the stage. So this is funny because usually we're on Zoom and Rose and I keep our eyes on each other's, you know, rectangle to see what our expressions are and like when we're going to cut him off.

2:52So yeah, this is going to be a little different. So we can do this though. So what has been going on? What do we have any hot news to share in the world of materials? There are always material announcements. I mean, I think that's our number one. Go to, right? Yeah. Yeah. The latest rumor that we've heard, as some of you have listened to the show for a while,

3:23know that there's been the great Custer Feldspar crisis of 2023, that the mine closed suddenly in October. It seems like it's dead. I haven't heard any updates for it. And it's left us in a difficult spot because that was the last domestic American potassium Feldspar, which is incredibly important for clay bodies. And so we've been left with only two imported. And now there may be a third. We may have a new entry into the market. We've received word that Emrys is going to release

3:59another product on the G200 label called G200 hashtag 2R number sign, 2R is as old people know it as, which is coming from India. So it is still imported. It's not a domestic source, but it seems like they may be going for a competitor for Mahavir. Mahavir is one of the Feldspar that's been around for a while. Laguna, the American supply company, pretty much had exclusive importation rights of it.

4:33And this is now Emrys, which is a huge mining company that has most things. And it sounds like they've tapped into an Indian Feldspar, which will be good. I mean, I don't know how quick it's getting to the market. We've heard that it's from American suppliers, that it is coming in, and it should alleviate some things in the long term. The good news is I've seen the chemistry. It looks good. Um, you know, I, I know a lot of people here had a very passionate relationship with Custer Feldspar. Um, I didn't like it. Uh, I think a lot of people were addicted to it cause it was been

5:07around and it was cheap. Um, but it had some chemistry problems, challenges, shall we say? And these Indian Feldspar seem pretty pure. How many of you out there have started recalculating glazes in your studios for this? Yeah. Yeah. So the Harvard Ceramic Studio, we just finished up, um, our Cone 10 glazes. And I think we had to recalculate maybe 25 of them all to NefSci. And it was a lot of work and shout out to Casey Zhang, our, um, glaze facilitator for helping

5:38us with that. And it was a lot of testing. Um, but we got almost everything, um, looking great. The only one we can't quite figure out is like a eerie blue floating blue kind of moment, you know, with the, uh, lots of revelants and, but yeah, streaks and bubbles and a lot of movement. And that's coming out like really purple. Um, but, uh, that, that reminds me too when, yeah. Oh, what did it, did something strike you? Yeah. His silica levels are probably off. Damn it. We just, we just had that. I've got to make a call. We just had that with

6:15a client. Well, yeah, because, um, that, that if you're, if you're using, so that streaky effect that everyone knows, like makes glazes look all cool. That's the hair spur, that kind of thing. Yeah. It's, it's a, it's a chemical reaction called phase separation. Um, and what you're actually getting is two different compositions of glass, even though you only have one recipe. Those two compositions are called phases and they are attempting to separate. And so although you have one recipe, it's actually two different compositions. Well, one of the phases is always inevitably a little bit, uh, or is opaque and slightly blue. And so if

6:48it's silica levels are off, it's, it's generally affected by silica levels. Higher silica levels will tend to face separate more and lower silica levels will face separate less. So I'd probably have him check his silica levels. I sure will, Matt. Thank you. Yeah. And it happened to both cone six and cone 10. They just turned up purple for some reason. So mysteries abound. Um, but that brings up, if you are, um, thinking about a question to, I just use two glaze names, but that's really kind of difficult to do. So if you can use as many descriptive words as you

7:18can, rather than, you know, you're floating blue, there are a million floating blues are also, it's also called money blue at the sales. Well, the theory is that anyone's going to buy a blue pot out of the sea of brown pots at our sales. So, um, but if you can just use more descriptive terms, I would probably help Matt and Rose out trying to figure out what they need to answer. Absolutely. Okay. Are you ready? Yeah. Do people have questions? We've got a microphone set up

7:48over here. Don't be afraid to be the first one to ask a question because they're all, everybody's staring at us. We need to use the microphone. So if you can line up to the microphone.

7:58Oh, great. Oh, no, they're rushing the door. Oh, no, they're rushing the door. Stampede. No, wait, don't yell, don't yell stampede in the crowd at the end. Don't yell that. The fire marshal's here. Shh. Hi, thanks so much for being here. I'm Amanda Bartell, and my question has to do with glazed substitution, glazed material substitution. I finally found the perfect white glaze, and it has Gerstle borate in it. And so I know that substituting isn't easy because, like, you can use

8:28Fritz, uh, what, 3134, but the alumina is off. So is there a way to find, uh, recipe substitution, substitutions that will, like, account for all those different, uh, distributions of chemicals and elements? Yeah. Yeah, the Gerstle borate is the other one that's been a big problem in the last year. Again, this one really hasn't been published. I think we've mentioned it on the show, but as many of you know, Gerstle borate was a mine in Death Valley, California. The mine actually closed in the

9:0190s, and it never reopened. Oh, I remember. Yeah, no. Everyone lost their mind in the 90s, yeah. Yeah, like, when it closed, it was, like, traumatic. And what had happened is, once again, the Laguna, the supply company, found out that there was a large deposit that had been mined but not processed. They bought it, like, 15 or so years ago, and then they reprocessed and packaged it. And they'd been selling that deposit for years. Um, and they swore they had this huge deposit. I'll never forget, I was there touring Laguna's facilities in 2018, and the person giving me the tour said, oh, here's

9:32a stack of Gerstle borate. We've got a 20-year supply. And I looked at his, that is stack of pallets. And I was like, yeah, 10. Uh, and we were both wrong. It was five. Um, so yeah, they've now sold out of everything that they had. Um, the catch with Gerstle especially is it has a very particular chemistry. Anytime you're using something like Gerstle borate, you're trying to get temperatures down generally from, you know, glaze chemistry is based in cone 10, and anything under that we need to convert down, it's generally done with this chemical boron. 3134 is generally the accepted

10:08answer for that particular solution. Um, it's the exact amount though is the hardest part because that really depends on literally what is the chemistry of your glaze. Those of you who listen to the show know that you, that the chemistry of the glaze is what matters. I know there's people out there who don't want to admit to this reality, but chemistry, but chemistry does apply to what we do. That's what it was 100% responsible. And so you need to match it literally on a molecule by

10:41molecule basis. Um, and that's sort of the basis of glaze chemistry. You can try a one-to-one substitution. As you say, they generally don't work. Um, glazy.org has a calculator where you can say, here's what I'm doing and substitute it with another one. I forget whether it's, it might be Patreon only. You might have to pay for it. Um, but it gets close. It's not perfect. But of course, the real answer is you got to learn your glaze chemistry, everybody. Um, and that's the harder part of doing those conversions. Once you get the conversions down, that's what Kathy was talking about. Yeah. So we, we did, uh, our conversion before even the Custer Feldsfire thing, uh, with, um,

11:18Gillespie. Yeah. So what do you, do you recommend that? I mean, just say yes.

11:26I'll give you the answer. Just say yes. What a brilliant idea. Gillespie came around when Gursley first went out of the marketplace and, um, Gillespie was just another substitute, similar chemistries, but actually knowing what the chemistry of Gillespie borate is, is a little bit random, funny story. I was in a conversation with the owner of, the company, Hamill and Gillespie, uh, a couple of months back. And we're sort of just trading emails. How are your kids? Blah, blah, blah, blah. And then I said, uh, Hey, by the way, do you have a current chemical analysis for Gillespie borate email chain stopped? No more

12:01answers. And that was the end of that. So it should be okay. But knowing the chemistry of those different materials is the hardest part because no matter fun fact for everyone, no matter how much anyone at your supply store or online tells you that this material is a one-to-one substitute for another material, they're wrong a hundred percent of the time. Sure. There are some materials that are close like Mahavir and G200EU. They're going to be close. Are they perfect? No. One of the big

12:36problems with losing Custer or Gursley is that they had fairly specific chemistries that if you don't know how to go back and match it, it becomes really tricky. We were visiting a potter last fall who swore that they had this one magic bag of feldspar that they couldn't, they were terrified they would run it to the end of because that's the only way they got their, their chun glazes. Well, chun glazes are just phase separated glazes, this streaky effect. And literally they were using Custer and Custer has more silica. And like we were saying to Kathy, take the silica up and that sort of

13:06solves the problem. But yeah, it's try, try those calculators. But at the end of the day, we all got to learn our chemistry, eat our vegetables. Thank you. She's like no help.

13:21Next. Hi. Hi, my name's Rachel Hill. I'm from Powder Springs, Georgia. I have a question. So I recently joined a collective so that I can have access to their gas kilns or reduction kilns. I have only done cone six at my own house and I was considering buying a small test kiln because I need to test, test, test. So, um, I was wondering what, would it be a waste of my time to buy like

13:53an oxidation kiln to fire these glazes when I, the goal is to do reduction with them? What, what would the, like, what would, how would it speak to each other, like the oxidation versus the reduction in the glaze testing? In general, not much. Well, I mean, you get color differences. You get some, some effect differences. I mean, we, we use, we will run through our cone 10 reduction through the, our little, uh, scut test, um, kiln just to make sure it does something close to what we were hoping

14:27for. Yeah. And then, you know, it, especially if we're waiting for enough work to accumulate, to be even, to be able to do the cone 10. Um, so we get like a little information, but they don't look anything alike because of oftentimes maybe a celadon will look close, but a huge difference by the end. But that reduction really does make a huge impact on the final result. Yeah. But I mean, you can, I think if you have a small test kiln and you're firing oxidation, you get, you get a good idea of what that glaze is doing. Um, and then you can put it in the reduction and

15:01then you get to say, Oh, this is oxidation versus reduction. Look how cool that is. Cause sometimes they can be green and red or, you know, blue and purple and, you know, different, different colors. So I always like the variable of oxidation and reduction. Yeah. When we moved into our, we built a new studio a couple of years ago and we finally got the reduction kiln of our dreams and we're like, Oh, we're going to fire all of our tests. We'll make two tests, everything, fire everything in reduction. And then we didn't, um, because they mostly look the same. Yeah. Um, so, okay. Every, I see a bunch of people with notebooks in the audience, if you're listening. Okay.

15:33Ready? Okay. Silica, alumina, boron, lithium, sodium, potassium, magnesium, calcium, strontium, barium, and zinc. Those 11 elements are what make up 99% of all of your glazes. I think you need to say it a little slower. I said it really slow. They can listen back to the recording. Silica, alumina, boron, lithium, sodium, potassium, magnesium, calcium, strontium, barium, and zinc. Those are the 11 elements that literally make up your glaze.

16:04Okay. They are the glassformers that literally make the glaze and the fluxes that bring down their melting temperature. Of those 11 elements, 10 of them are completely unaffected by reduction as in they will be exactly the same in oxidation or reduction. The only one that's affected by reduction at all is zinc. Okay. So if you have a reduction glaze that has, yeah, I see some crystalline potters who are ruining their, their reduction up front. Um, but if you have a glaze that doesn't have any zinc in it, the physical chemistry of the glaze is going to be exactly

16:39the same in oxidation as it will be in reduction. Okay. So what are the differences? Why is there such an impression of oxidation versus reduction being different? Because of the colorants, specifically the colorants of iron, which is, which is what Kathy was talking about with the, um, the celadon and copper, which is responsible for copper reds, those two colorants change their colors in reduction. Iron will generally turn to blues and greens where it's naturally brown and copper will turn to red when it's naturally green, but it doesn't affect the base chemistry

17:13of the glass. If it's glossy, it'll be glossy. If it's matte, it'll be matte. If it's crystalline, it'll be crystalline. The other impression that people will often get for, um, oxidation versus reduction of like, Oh, I grow all these crazy crystals in my reduction kiln. Um, that has nothing to do with the reduction firing at all. That has to do with the fact that reduction kilns tend to have crazy thick walls. Our reduction kiln has 12 inch thick walls that cools really, really slowly because it keeps the heat in. Most people's electric kilns have two and a half

17:45thick inch thick walls and those cool really, really quickly. So one of the classic things that I hear people talk about is to do slow cooling in their electric kilns to try to mimic the effects of the gas kiln. So if you're using a reduction kiln, the colors may be slightly different, but you may want to put in a slow cool program. And there's dozens, hundreds of those all over the internet. Yeah. And tell he's getting excited. He hit the microphone. All right. I talk with my hands. Isn't it? I mean, another aspect of this though, is with reduction, when we look at those results,

18:17it's a lot of the information being given by the clay, especially if it's a iron bearing body, right? So that, that canvas that the glaze is sitting on is looking much different because of, um, dots and flecks and all that. And that's generally because of the iron. Most clay bodies have some sort of iron contamination. Dark clay bodies have a lot of iron. Well, well, we use a test kiln for where, where'd you go? Um, test kiln for, um, uh, our class that we run, uh, with, uh, Matt. Um, and we go through thermocouples a lot. So we did end up investing

18:53in an S thermocouple. I mean, we had to put up tuition by like $500 person to be able to pay for them, but yeah, we did it. We took the plunge. What you got? Hi, Matt and Rose. I'm Dorlisa. You know me. Um, so my question is about stains and the cadmium that is in them. Um, and I know Matt is going to roll his eyes. I'm just going to roll over and die.

19:24Go on. Because I've noticed that glazes that include a bright red or orange stain, they bubble a lot. And then I also put an orange stain into a clay body, porcelain, and it bloated. Is it refractory?

19:44Do you know, I mean, Rose worked in stains for years. What's the glaze that didn't go well? Was that six or 10? Uh, cone six. It's cone six. Okay. I have one. I use the red and orange, all the reds in a cone six transparent. Worked okay. They're, they're awesome. Yeah. Awesome. Did you ever have bubbling back in tile? How we, they, they couldn't afford the red and the orange.

20:10Uh, so no, I mean, we, we avoided those really because of cost mostly and then, um, problems to the roller hearts. They just didn't like the fast firing, but we were only sticking with one type of glaze. So our, and our glaze had zinc in it and it was just a mess. So, um, we tended to avoid those in my tile days. Yeah. It's a question we can't answer at the end of the day. We'd love to have somebody from Mason come on the show. I doubt they're even here today to answer them. Uh, the encapsulated stains,

20:44you know, my, my constant refrain with our students is stains are not stable colorants. They are stabilized colorants. Uh, but that means that they can react with things. So are they refractory, which is the opposite of flux oftentimes, but not all of them are, but it is a consistent problem with, um, red stains and orange stains that they will react badly. Crystalline glazes do not work well with them because crystalline glazes contains zinc and zinc will tend to irritate the stains and make them bubble, but it happens in just plain old glazes. Um, we deal with that all

21:15the time with clients that, you know, want specific colors, um, from our consulting work. And we're dealing with it right now of, they want this one color and it bubbles when it's too thick. Um, are they stable? I don't think that the companies would be selling them if they weren't stable. I have heard tell, this is the ultimate of rumor though, that, um, the company assumes people would never put these on the insides of pots. Um, uh, the, this is what we hear. Um, so again, that's purely

21:50a rumor. Why did you hear that? I cannot list my sources. They'll put out a hit on me. Yeah. They already have that. It's okay. They haven't found you yet. Great. But yeah, I would be cautious about it. The one trick, uh, that we have learned with the stains, um, and shout out to our friend Alex Zircopax for this one is that if you add 2% Zircopax to your glazes that bubble, it does tend to, uh, reduce the total amount of bubbling. Um, so that can make them behave a little bit

22:20better, but it's not a, it's not a perfect solution. Well, Zirconium silicate. Zirconium, sorry. Zircopax is dead. Yeah. Zircopax is a brand name and they're not making that anymore. Ultrox or Zirconium silicate. Thanks. Hi. Um, my name is, sorry. Uh, my name is Allie. Um, my school's glossy white glaze for reduction works really well on our standard clay body, but I've been using wild clay as a slip and I'm getting lots of pinholes and it's, uh,

22:52Maryland clay. It's red. I'm assuming it's something with the iron, but is there anything that I could do to like mitigate that? I'm also like after it's dried, like rubbing over the pinholes on the surface when it's dried before I put it in the kiln, but is there anything I can do chemistry? Are you firing it? Uh, it's reduction. It's wild clay. Yeah. I was about to say, we're the wild clay people in the audience. Okay. Put down everything in your hands so you don't throw it at me. Um, wild clays are consistently a challenge, shall we say? We'll use the

23:26optimistic language. Um, you don't know what's in them, but there probably is quite a lot of iron and iron the same way we were talking about how it can be reduced. If you fire iron and don't reduce it properly, it will release oxygen into the slip into the glaze and that will cause bubbles. The next question actually is, I can't actually promise that what you have is pinholing. Um, one of the things that, you know, we really need to get clear in this community is pinholing is not one glaze flaw. Everybody acts like, Oh yeah, it's just pinholing. No pinholing is at least four separate

23:59problems that all look similar that everyone just calls pinholing, but pinholing itself is an application issue. If it's being caused by iron or copper, it's blistering. If it's being caused by titanium, it's pitting. And sometimes you just get what we call body voids, that there are spots in the body where you don't see the hole that is in that clay. And it just, the glaze just doesn't apply. It looks that way. Saying that it's high iron makes me think that it's blistering and that it's probably just the iron in that clay. The reduction should help, but it doesn't always help. Um,

24:33if the glaze is working on the one clay body, not the other, what you may need to do is adjust the water content in the glaze that you're applying because glaze application is based on the absorption rate of the clay body. If you put a slip on top of it, it is now based on the absorption rate of that slip. And so the, the glaze coating, literally how much glaze you're applying is very different just by having the slip on. Thank you. Sure. Um, hello, my name is Lori. Um, I had mixed a glaze

25:06recently for our studio. Everything was fine the first week. And then a couple of weeks later, it turned to pure gloop and thickened over time. So I was just wondering what you had to say about, um, um, um, hard panning and resolving issues like that. I've been told that it was zinc, um, was the trouble, but I was just wondering what you had to say. Madam viscosity. Great, great question. Um, do you have any additives in your glaze? Um, yeah, there was really low

25:37percentages, like 0.5% of cobalt, um, iron and chrome. Okay. Any like, uh, bentonite or uh, epsom salts or suspension agents? I had added epsom salts, but not bentonite. Yeah. Epsom salts, your problem. Oh, okay. And why?

26:00Uh, epsom salt is, uh, magnesium sulfate. And so it, did you add it as a liquid or as a crystal? Crystal. Crystal. Yeah. So it's, yeah, it's like a problem. Um, so magnesium sulfate's a crystal that you should be dissolving in water if you're adding to your glaze, but it takes just a small amount to take your glaze from thin and creamy to like cottage cheese, um, really quickly. Yeah,

26:30that's coagulant. So it takes it from nice and smooth and dispersed and clumps everything together and it will just keep doing that as it's sitting in the glaze. So that's why it's getting worse and worse and worse. So, um, I would recommend you add it if you have to add it. You don't always have to add it. Um, add it in liquid form, make a saturated solution. So, you know, a hundred grams of water, a hundred grams of epsom salt, use hot water so you can dissolve it and add just a drop at a time.

27:04It's really not that much. Um, if you're working in bigger batches, it might be a few more drops, but if you're doing it in like a test, um, of our tests are a hundred grams. So if you're doing it in that, you probably really don't need it in that amount. You're just going to make it application, uh, a nightmare, but, um, in bigger batches, you can add it, but it's just really small amounts because it's going to keep coagulating over time. Yeah. We're pretty, uh, you can, but it's not the

27:35same. It's not like you just magically make it go backwards, but you can add dispersant to thin it out again, but then, or Darvin. Yeah. Um, but it's not, it doesn't backpedal and be the same glaze anymore. It's drinking a beer to take down your hide, get rid of the pills you popped earlier.

27:57Um, yeah, I'm, I'm pretty skeptical about glazes that have epsom salts as their recipe by default. I, I only add epsom salt if I absolutely need it. It's not like, uh, if I can avoid it, I will long-term glaze maintenance. It's okay. But if you've got a fresh batch, start with basic water content, allow it to age. Number one thing we all do wrong with our glazes. Everybody is you should be waiting at Kathy hates this. She's, she throws things at me when I say this. You should be aging

28:28your batch of glaze for three days before you use it. Or even when you make a glaze test, you should mix it, let it sit for three days and then adjust the water content. Um, but we did it finally. We did. I could, I mean, I can't argue with it cause it, yeah, did things change from the materials room to rolling it out on the floor. And, um, so it's really helped out a lot. And we also took the opportunity of having to recalculate all these glazes to then really getting down to having what

28:59our water content is. And we never had that in a studio with 85 glazes. So it's really making a difference. And monitoring that water content. Yeah. As it ages, it, it can shift. So water is an ingredient people. Water is an ingredient. Thank you. You're welcome. I met you at the bar the other time. Yes. I'm Mark from the bar and also Mark from, uh, Tucson, Arizona. I have a variation on the

29:38mason stain question. So same red stain. I've been chasing, uh, surface defects, uh, going through, you know, I've added zircon or zircopax, uh, up to 3%. Got it to where the surface was almost perfect, maybe good enough. But you know, my techniques were adding the zircopax, uh, reducing the stiffness. But what, what would you suggest in trying to chase an orange peel kind of problem on a glazed surface?

30:08Again, it depends on exactly what the base glaze is and why it's orange peeling. Problem number one is, is the bubbling bubbling can look like orange peeling. Um, the second problem as to the previous question is stains are generally refractory. For those of you who are not familiar with that term, our glass warmers are very high temperature. So we use fluxes to drop their temperature, but there are materials that are called refractories, which are the opposite of a flux. They literally raise the melting temperature. Stains tend to be refractory. So they're going to raise the inherent temperature of your glaze. Well, because they're combined with other materials, they're just not, you know, they're

30:42multiple ingredients. They're not just a blue. Right. It's not just coal. Like they'll make it into a spinel or some sort of zirconium, um, base. So if the glaze is too stiff, you may need to adjust what we call the chemical temperature, um, which is the temperature that the glaze actually wants to be fired to. Like we all have this very confident relationship. Like, Oh, I'm cone six, I'm cone 10. Yeah. Those numbers are almost completely arbitrary because every glaze has a temperature that it wants to be fired to. And some of them are a little bit over content and some of them are a little under content.

31:15And you can fix that by either a firing hotter or be adjusting your temperature, which is sort of what the boron conversation was about earlier. Um, but if it's, if it's pretty orange peely, it sounds like it's, um, it may just be the reaction of that stain. And this is the question, um, whether or not that stability, the other thing, which got mentioned briefly is if that glaze has any source of zinc oxide, or if it's got any magnesium, talc, dolomite, mag carb, forget it. You're done.

31:46Um, because those, although the company does not say it on their literature, those encapsulated stains do not behave well with anything with zinc or magnesium in it. Yeah. This is a pretty simple sodium calcium. Uh, you know, had success lowering the silica alumina ratio to the fluxes, but I didn't bring up the boron. I'll give that a shot. Yeah. Bring it. It doesn't have to be a lot, but just enough to smooth it back out again. All right. Thank you. Yep. Hello. My name's Liz Paley. I'm from Durham, North Carolina, and I make a lot of pots where I start with a cylinder and I add a contrasting

32:21slip. I cut lightly through the slip and then I stretch the pot. And at some point I thought, wouldn't it be cool to have, and what, what you end up having is a slipped surface. And then you have, you can see the texture where the clay stretches, right? So you have really interesting, um, surface contrasts. And I thought, wouldn't it be cool to have a glaze where I have the slip instead of, so I can see the texture of the clay as it pulls apart. But instead of the contrasting slip, I have a glossy glaze and I tried it. So I, what I need to be able to do is apply a glaze. I hope it's possible that I can apply a glaze to a leather hard, or to a, a wet surface,

32:55wet clay surface, stretch that out. Of course, I'm using a heat gun to keep the pot from collapsing, um, and then fire it and have it look like glaze by the time it gets fired to temperature. Um, I've tried it once and what happened was the glaze wasn't stretched, you know, it doesn't stretch. Um, so it ended up melting the way I wanted it to melt, except there were cracks all the way down the glaze. The pot wasn't cracked, but the glaze was cracked. Is it possible to, do something like this where you could have a material you could apply at leather hard, or not leather hard, but wet clay, stretch it while you're heat gunning it, and then fire it

33:30and get a melty glaze. Can I ask something? So when you say it was cracked, it came out cracked, the glaze, what, what do you mean? Was it like shivering off? No, it stuck perfectly, right? But when, when you stretch the pot, Right. And you're heat gunning it, it dries, the material, it dries everything out, it dries the clay out, it dries the, the slip out, it dries the, the glaze out. Um, and so as it stretches, it, the glaze just kind of split. I mean, lots of things are splitting. The clay is splitting too, but it doesn't, I wouldn't call it, I mean, what you get are

34:01discontinuous lines when the glaze melts instead of a continuous line of glaze. And this happens during the stretching. It doesn't happen during the firing. So it's going, it had no problem sticking to the pot. Okay. But it didn't stick to itself. So did you glaze the whole pot again or no? No. Okay. No. So, so I threw the cylinder, thickened up some glaze, applied, it wasn't actually that thick. I brushed some glaze on, um, and then cut, cut my lines through that and then stretched. And so there was no glaze where the pot, where the clay was stretching, but there was glaze on

34:34the stripes. And then the glaze splits where it's weakest. I'm sorry, the clay splits where it's weakest, right? So the glaze stayed intact, but the process of stretching it, the glaze on this wet clay surface led to just, you know, raw clay. Why not go back to that slip thing? That sounds great. It's so great. Because I want shiny. It sounded like that was going great. It does go great. But I want that. I, you know, I'm really interested in getting that shininess. And if I, you know, I can't dip the whole thing in glaze because then I'm going to lose the, the texture of

35:08the stretched clay. Something with a teen? Yeah. I mean, on gobes as vitrified slips are a variable. On gobes, just that term for it's the, sort of the land between slip and glaze. That certainly could be it. What was, what was the glaze? Was it something you made yourself as a commercial? It was something I missed myself and it was just something I, you know, like some blue something.

35:31I feel like it's car talk. The car is blue. Is that on glazey? Some blue something?

35:38The first problem is, is that you probably to get it to work, need to go back and treat the glaze more like a slip. So again, start it with a real low water content. Try to get it much more custard like. So we always say you sort of start a glaze test with about 60% water. You may want to mix that up with 30% water. Let it be a little pasty, let it age a couple of days, then add in 10 more mils of water and sort of see what it does. It's got a little bit more viscosity to it.

36:10The glazing of itself might be hard though, because part of why slips work is that slips are literally liquid clay. And so they have very similar shrinkage rates as the clay body itself. And so it's not that you can't overcome that with glaze, but most glazes can have somewhere between zero and 20% kaolin, which is what clay bodies are mostly is kaolin. And so whereas the slips can have 80 or 90% kaolin. So they're just going to, they're going to adhere much better. But I would go back to the viscosity of what you're applying and just see if you can start

36:43with it thick, try some experiments, start real low, try some application, slowly add water content and see if there's a sweet spot with just water content. Yeah. Okay. Thanks. Yeah. Thank you. Hello. My name is Cassie and I'm from Moscow, Idaho, and I have all the questions. All of them? All of them. Rose. I would choose one, but it's two parts. So I have a handful of tried and true glazes that I've been using and making for several years and they have lithium carbonate in them. And recently my lithium carb after, you know,

37:17sitting in the glaze bucket for a couple of weeks, the lithium carbonate starts precipitating out and making these really, really beautiful crystals. Um, but, but then they're crystals and they're not in the glaze. And so, so my question first part is one, why is that happening suddenly? Um, number two is how do I get those dang crystals back into my glaze? And three, my, my last part of my question. Um, it is appearing very clear to me that I

37:47need to start phasing out lithium carbonate in my glazes. And how would you suggest I do that while keeping the super beautiful, awesome, lustry magicness of the glazes? Well, it's called increase your glaze budget. Yeah. Yeah. Wise investments. Find a sugar glazed daddy. You don't have to get rid of it. Yeah. Yeah. Ah, that was yours. Oh, that's why she buried me. Oh, this whole time.

38:18Um, the lithium problem. Yeah. I mean, the prices are through the roof. Uh, Rose and I just bought our first EV. So you can thank us for that. Um, you know, love EVs, but the EVs use lithium and cobalt nickel, which is why all those prices climb and will continue to climb. Um, the crystallization happens because lithium carbonate is soluble, uh, in water. And one of the first things everybody needs to understand is that the reason why we use the materials we

38:48do in glazes is because they're not water soluble. They don't dissolve in water. They're just rocks suspended in water, teeny tiny little rocks that look like a liquid, but they're just rocks. When you put something that is water soluble, like lithium carbonate or soda ash or pearl ash, um, they literally dissolve in the water and they are now in solution as it's called, which is exactly what happens when you add sugar to your coffee. It just, it disappears. It doesn't disappear. It

39:19dissolves. And it's now in solution as opposed to what glazes are, which are suspensions. Why does it precipitate out? Oh, they can precipitate out for a myriad of reasons. The most common one is just ambient temperatures. Um, this is an odd time of year for that to happen, but the classic one you see is that if you hang out on ceramics, Facebook in the Northern hemisphere, all of a sudden in November, you see all these posts that are like, what are all these weird crystals growing in my glaze? It's because we all have uninsulated studios, uh, and it gets cold at night. And when the temperature drops, you

39:52cannot, you cannot keep as much lithium in solution at lower temperatures. So it precipitates out. And there's literally nothing that you can do about it. We've probably said this on the show before, but all of those people like, oh yeah, I re-crushed it up, right? Assolved it in water. You're wasting your time. Uh, don't even bother. Once it's precipitated out, it's gone. Move on. Um, it just does not work that way. Um, so yeah, there is that lithium carbon. It is a funny material. A lot of people act like it's like glaze magic. It's not. The problem is lithium carbon. It represents a group of materials called the

40:28alkali metals. And those are lithium, sodium, and potassium. Those materials generally come in the form of feldspars. Feldspars are rocks that contain the lithium, sodium, or potassium, but they also contain silica and aluminum, which is what makes them not water soluble. Um, and that's why that we use those feldspars because they're the cheapest non-water soluble type of that material. Lithium carbonate is basically pure lithium with some carbon dioxide attached. And that's why it dissolves.

40:59It can lead to interesting chemistries and there are ways to get around it. There's a bigger conversation about the glaze chemistry of it all. Who would have seen that coming? Um, but there's not, again, a material that's really easy to substitute to that end. There are some materials that sort of lean that way, like Frit 3110, but again, you got to match chemistries and that's where all the things come in. Um, so you can get away from lithium carbonate, but I will say lots of people, again, they think that like, Oh, you add 5% lithium carbon and your glaze goes crazy and makes

41:31crystals. It's not because of the lithium. It's because of the way it changes the chemistry of the entire system. And that can make it do it. And you can do that with sodium. You can do with potassium. It's just that lithium is just this convenient source that everybody's become addicted to. But now, I mean, what is it like $200 a key bump? Uh, you know, everybody's doing, selling, selling grams of lithium out back of the club at Anzika. I've been to those parties, everyone. I've been there. Um, not this trip. No, not this trip, but it's a tough situation. Thank

42:06you. Thank you. Hi, my name is Melissa. I'm from Tallahassee, Florida. Um, just want to say thank you guys for existing. Uh, but yeah, like I literally listened to like no other podcasts besides this. Um, so I have been, um, helping, uh, a studio, uh, with making a low fire matte glaze and I've been test, test, testing and, uh, just wanted to reach out for, um, any tips

42:39on how can I make those, um, true matte glazes, um, more matte, like more matte looking and less, um, shiny. Did you say low fire? Yes, I did. Yeah. I have, I mean, I don't know if you want me to get into numbers. I have the numbers in here, but, uh, just was looking for like tips, you know, I was keeping the bottom level higher than 0.45 and stuff. So, yeah, the, our low, um, fire matte glaze is possible. Yes, they, they absolutely are. The issue that

43:13we get down to is low temperature is really, really tricky. So when we're talking about the structure of glaze chemistry, I know all these people, Oh yeah. Cone six, seven, cone 10, whatever. Cone 10 is where all glaze chemistry is based. Okay. To understand glaze chemistry, you look at cone 10 and every temperature beneath that, like cone six or cone five or cone two or cone O four is based on the structure of chemistry at cone 10. So those requirements, like you're saying of the boron that keeps coming up, you need just a lot of boron to get it to work

43:47at cone O four. And what materials you can use are really, really tricky. Um, uh, I like frit 3195. We're talking about 3134. There are a lot of sort of crazy frits out there, but again, with sort of loss of Gursley borate and, you know, what people try to do, it can be rather hard to do. And we've definitely made them, but it's probably more of an in the lab situation that is practical. Um, you know, we use sort of crazy materials and, you know,

44:21do weird things and, you know, Rose and I do crazy amounts of drugs at night and experiment with glaze chemistry. Um, Yes. Cause that's so me. We're doing white powders. You told me it was drugs. Um, but yeah, it, it's possible, but it's, it's a really tricky one. Yeah, no, I was able to achieve like a really nice matte black, but then when I was getting to the white, I was using, um, zirconium and then that's more like refractory. So then I, I'm thinking I'm going to have to add even like more boron to that to like match it. So just more,

44:53more testing. And that's what we were talking about with the stain questions earlier. And it's always that sort of back and forth to try to balance it. Sounds good. Thank you. Good luck. Thank you. I appreciate it. Thank you.

45:05Hi. Thank you. Um, I had a question about hard panning or dead panning, um, involving the Epsom salts. Our glaze doesn't like involve, we don't have, it's like Epsom salts isn't like one of the ingredients, but we have been using it to help with the dead panning. Is that a, and we use a liquid form of it. Is that like the go-to is Epsom salts or do you have other, um, uh, I mean, if it's hard panning, you can use bentonite, but that's, you know,

45:38you should add that as a liquid too, probably or, or at the beginning or yeah. Or when you're start batching. Um, I mean, usually for, for my go-to, it is Epsom salt because we're not keeping large amounts around. Um, and it's a quick kind of easy thing to do instead of fooling around with, oh, should I add half percent of bentonite or should I add like go up to two or, um, but it, you know, some of your materials, if it is, if it is hard panning, like look at your materials,

46:09do you have kaolin or help suspension? Do you have other things in there to, to help remedy without adding Epsom salt is probably a good, good idea. But, um, yeah, it's usually Epsom salts easy. Yeah. Um, just not great for longevity. Yeah. Bentonite on a new batch. Yeah. Put 2% bentonite if you don't have it. Um, but I, I still go back to what we were saying earlier of really look at that water content, mix the glaze first at a low water content, let it age because a lot of time hard panning can come from excess

46:43amounts of water. Our clases, our glazes stay suspended because these kaolin particles in there have a charge that basically keeps everything bouncing like a beach ball at a concert. But if you have too much water, it literally creates greater spaces between the particles. And so like, you know, it's like when the beach ball gets hit to the back of the field and there's no one there, it hits the ground. And so, you know, if you have too much water, it's going to space things too drastically. So try to minimize the water first, add some bentonite. And then for long-term, perhaps some salts is generally the way to go. Yeah. After three days, you do like the specific

47:16gravity and like do all of the test tiles and stuff. Typically you should do specific gravity and viscosity together. Yeah. The real trick is the dirty secret is specific gravity is a useless number. Um, specific gravity means nothing without a second measurement called viscosity, which is how the glaze flows. And you can get a thing called a Ford cup or a Zahn cup. Um, but you see people out there like, Oh, specific gravity, specific gravity, specific gravity means nothing. Like it literally means nothing. Um, because every single glaze in the

47:49world needs its own specific gravity and you have to establish that for that glaze. So what we like to do is we literally start with a low water content, let it age, and then adjust to the glaze to where we like to work with it. And I, this is as a person that loves science, loves metrics. And I will still go to, yeah, you know what I like. Right. And then I will measure the specific gravity and the viscosity so that I know what I'd like. So in the longterm I can aim for that. But if people are using specific gravity without viscosity, you might as well just make up numbers

48:20and call it a day. Right. And that, that is literally what we found out in our studio that they, the glaze mixers had this list of all the specific gravity and just kept changing. And everyone's arguing with each other. And it was also a little bit of a, I think an old wives tale of, I was buying giant amounts of Epsom salts and they, they were mixing it up in solution and just blindly adding it like every glaze needs it. And I'm like, Oh my God. So now we got that cup thing and, um, that's, it's like 25 bucks or, and, um, it doesn't look like it should be 25 bucks,

48:56but it's really helpful. And it just takes a minute to pour the glaze in and you have your stopwatch and you just time how long it takes to pour into the bucket. So I learned things. Figure out the water content that you like. Viscosity and specific gravity are great for long-term glaze maintenance. So if you're in a studio and you've got a big trash can full of glaze, right? What, when that bucket's getting down three quarters or half, that's when the people maintaining the glaze should be going and checking the specific gravity and checking

49:28the viscosity so that you can bring the water back up. Cause as people dip, as the glaze ages, water will evaporate and it won't perform the same. And so you can go back, add some more water, add some Epsom salts, add some Darvin too. Darvin and Epsom salts will adjust the viscosity. Whereas just water will adjust the specific gravity. Okay. And viscosity. And viscosity. Yeah. And what was the name of the cup? It's either a Zahn, Z-A-H-N cup or a Ford cup, like the cardboard.

50:01They're basically the same thing. Yeah. I mean, the Zahns are a little more common. Yeah. Thank you so much. Thank you.

50:10Hi. I'm new to pottery, but I haven't even been doing it a year. So I'm having issues with getting cracks in bisque wear and not S-cracks. So I've done some research online. They talk about using fuzz from your dryer or shimming up paper, you know, painting with vinegar, not painting the cracks with vinegar. I bought bisque fix, but I'm just trying to figure out how do you repair a crack because each piece I make is so important to me because I'm so new at this.

50:41I was going to say start over, but.

50:47Well, let's talk about your drying. How are you drying is the number one. I dry it slowly. I wrap it in plastic. And then as it gets more and more dry, I make the plastic a little looser and a little looser until it gets to, you know. Do you flip? Yes. Okay. Because the number one thing that most people are doing wrong is drying. People commonly sort of see drying is like, hey, just let the piece dry. Drying really needs to be babied. And plastic is not always the right media. Our favorite material is a cheesecloth. Cheesecloth,

51:22if you dunk it in water and then wring it out, will tend to allow the piece to dry very slowly while keeping a consistent relative humidity. And that'll be your best friend. As to your actual question, Kathy's not wrong. Yeah. Start over. But, you know, after you've spent six or eight hours doing underglaze and decorating, you hate to go, I'm just going to put it in the trash can. And if it's not a big crack, you know. So it's just showing up in the middle of the piece or on the rim?

51:54Yeah. Well, this was like my most recent one. I was making a plate that was for deviled eggs. And so it's over one of the humps of, you know, where the deviled eggs would sit that it came out of biscuit and had cracked. And were those egg humps like added on like in short? No, what I did is I buy the wooden half eggs and then throw a slab on top of it and press it down until it creates the form where the eggs would go. And then I flip the plate back over and do the drying until it gets to bone dry. And then I'd underglaze it.

52:27Yeah. Maybe just be, I mean, and maybe doing all that on foam, you know, just thinking about if you can baby that a little bit more and thinking about what's straight. It didn't look cracked when I, you know, when it was greenware I put in for bisque fire. Oh, cracks show up. It came up out of the bisque. Any time in the process. Yeah. It's not correct to appropriate cracks to showing up in bisque. They probably happened some other time. You know, the classic, oh, there was no cracks all the way through the bisque and they showed up in the glaze. They were probably there before. It's just that,

53:00you know, firing. So all that stuff with the dryer fuzz and the shim paper is, or vinegar on either side of the crack is all just flip it and let it dry. Make sure it's drying evenly. Yeah. I mean, I kept flipping them, flipping it back and forth and I did have it on foam. Try the cheesecloth because it'll mellow how fast it dries and it'll keep it from drying uneven. Okay. Thank you. Okay. So we're going to, we're going to end the questions here because we've got a couple of minutes, but we'll, we'll do what we can. Hi, my name's Deanne and I'm kind of new to the whole, your podcast and all that. And I'm

53:35kind of afraid to take a class because I'm not mentally in that space yet. However, I do make my own glazes and I have this one particular glaze that is giving me hell. So can you speak a little bit to, so I put the glaze, whether I put it on straight bisque or whether I layer it over another glaze, it just dries up so fat, like it looks fine. And then as it dries, it just starts popping off and it's just so annoying. So can you give me some ideas on where I could look in my recipe on how I could fix this? Like, I don't understand what the problem is.

54:09How are you applying it? It's just so annoying. It doesn't matter whether I dip it or brush it. So dipping and brushing will have different consistencies to get the right application. So you can, for your... Mostly I dip or just like pour it over some, you know, another glaze, but usually I'll dip or I'll put another glaze, I'll put a glaze on and then I'll layer it over and, you know, dip a rim or something. And then an hour later I'll come back and look at it and it's all just like popping off. The rim is popping off or is it the whole thing?

54:40The rim is popping off. When do you dip it? Do you dip it after it, like right away when it's so wet or do you... It doesn't matter. So I've got the glaze dry, like the first layer dry, come back, dip the rim, looks great. Come back an hour later. It's like... You said you make it yourself? Yeah. Does it have zinc in the recipe? You don't have to blame everything today on zinc. Taking you down, Wayne! So I'm just saying... If you didn't get to ask your question, the answer is... What should I look at? I'm sorry, did you say that? What in my recipe should I look at to help me identify like what is causing the problem?

55:16And it also doesn't matter what clay body I put it over because... You're getting glaze shrinkage and people often miss that. Glazes absolutely have shrinkage. They're made of the same materials that our glazes do. Right. And it probably sounds like your water content in this case is a little bit too low and you're getting really high glaze shrinkage. But if you have zinc in it or magnesium, similarly talc, dolomite, magcarb, those will tend to have fairly high shrinkage and need a fairly high water content to get those to work. So if I added Epsom salts because it was deadpanning, then I might have caused my own problem?

55:51It could be adding to the problem. Yeah. Okay. So is there any way... I don't remember. Is there any way to come back from that? No. Right. Once you've added magnesium? No. So basically... Suffers to chase your downers. Trash the bucket? Probably. Okay. Yeah. Do you measure your water content?

56:09Do that. By testing? Do that. Yeah. Okay. So I do have another question, if that's okay. But can you hold... Actually, we've got to get through everybody else for the show. But we'll... Thank you. Thank you. Hi. Thanks. I'm Andy from Hudson, New York. I've been experimenting with crystal glazes, Conten. I've tried a couple of porcelain slip casts. And I have tried a few recipes and a few different firing programs. And what I have consistently is crazy. And I'm wondering... I have tried reducing silica.

56:40I've made up some stuff that has no basis in chemistry to try. None of it works. Can I recommend chemistry?

56:48No zinc. No. Aside from the pat answer, reduce, you know, increase your silica by 5%, are there any other tricks that we should try? Well, I mean, the first problem is crystal glazes as a whole pretty much tend to craze. They tend to have very low silicon aluminal levels, which are more likely to make them craze. The second problem is crazing is a relationship between your glaze and clay body. So you... It depends on the clay body it's on.

57:18This is why we have the classic problem of, oh, this glaze crazes on my porcelain, but not on my stoneware. It's because that clay body, this porcelain is a thermal expansion of X, the stoneware is a thermal expansion of Y, and the glaze is a thermal expansion of Z. If the discrepancy between those are different, it will just create that problem. So at the end of the day, it's a clay body problem, but you can try to keep it as thin as possible. That can certainly help. Now, does increasing silica help? Yes, but... But that's why you'll see that, you know...

57:50Right. You mentioned increasing alumina. Is that... You can, but the problem is that crystalline glazes are very sensitive to alumina increases. So you might not... But you can try... We've got a recipe you can find, like, CMW high crystalline on glazing that tends to do better. Okay. Works well at content... Or high clay crystalline. All right. Thank you. Yeah, absolutely. We're at time, so real quick. Okay. Hi, my name's Roz O'Brien. I'm from Harrisonburg, Virginia. And I just opened a community studio, and I'm formulating glazes for it.

58:21And I'm wondering if you guys have any advice about what to use or what to avoid in that kind of environment. I basically have a blank slate. Keep it simple. Yeah. Okay. Like, how?

58:34As few materials as you need to stock. Yeah. Try to get your glazes to use as much of the same materials as you can. Make your life a lot easier.

58:45Mixing. Buying. Storing. Yep. That kind of thing. Kathy, any other thoughts? No, just... I would just, you know, shop through glazing, finding things that look interesting to you, but keep noting what the amounts are. I mean, our glazing, we have our prices for our supplies. Yeah. So I can look at a glaze and see how much it's going to cost. And I think I've talked on the podcast before, like last year, our average five-gallon bucket was between $40 and $60.

59:16This year, it's $120 and $240. Jeez. So, and that's because I just haven't had a minute to, like, break it to the net. I'm getting rid of all those ones. But, you know, you'll start to... If you can put in those, that cost analysis into the Glazy Org, it'll really help you out, too. Yeah. Okay. Great. Thank you. Thanks. Hello. My name is Benny. I'm from San Francisco. I just work in a comedy studio, and I have a couple of questions about, like, my underglades.

59:51So I've been using underglades for a while and never have, like, any problem with, like, clear glass on top. But only one color have a problem is lavender. I use a couple of brands and still have a problem. The problem is, like, when you apply the clear glass on top, it's blister. But if you don't have any clear glass on top, it's totally fine. So I just wonder, like, is it because of substance in the underglades or the clear glass itself? What temperature are you firing? Mid-range, cone 5.

1:00:22Cone 5. So, I mean, that's the thing. It's like when we started firing those underglades that are meant for 04, you know, up higher, the company didn't say a whole lot about it. And then just more and more people started doing it. So, you know, companies like Amoco will show you what happens. They just don't all work at higher temperatures. And that's just the name of the game. So, I mean, I do a million test tiles with one strip of clear. And I know Teddy Bear Brown and I are not going to have a relationship in the future.

1:00:53So, I mean, that's just from testing in the lilac, the lavenders, the yellows especially, some of the light purples are very refractory. And they just don't want that glaze on top of them. They either eat it up or bubble. Or the color disappears. Yeah. Yeah. So, I'm going to have to end it on this, but test, test, test, test, test, that's her line. It is. Thank you for coming, everybody.

1:01:33Discover additional inspiring clay content and insightful conversations on our Instagram, Facebook, and the Watch and Seek a YouTube channel. Make sure to follow and subscribe to NSEKA 360 on your favorite podcast platform. Visit nseka.net to become a member and donate online to cultivate meaningful and accessible programming year-round. Thank you for listening.