Callie Beller Diesel

We don’t like borax, but we love boron. Most sources of boron are bucket soluble to some degree or other, but borax is particularly bad for it. When the material is that soluble in the bucket, it affects the viscosity of your glaze how it applies. Picture this. You mix your borax based glaze and use some of it that day. It works great, your pots turn out fantastic, so you make a bigger batch before you make your next round of pots. While you’re spending 2 weeks (or more) making your next kiln load, the borax has a chance to dissolve in the glaze water. Next glaze day, your bucket looks like it’s thickened up a LOT. If your glaze gels and you do nothing, it goes on too thick and can run or cause crawling. You fire a kiln load of this ware, and you then have a bunch of shelves to clean. Plus, you’re out the work you spent 2 weeks (or more) making. If you add water to your glaze to make it flow properly, but for some reason your floating blue now is more of a yucky brackish brown colour. Again, you’re out the pots. Frustrating, but you’re a potter, so you’re undaunted! You then head to the internet and learn about how water content affects your glaze outcome, and you realize that the amount of water in the first batch was correct, but the rheology or flow that was a problem. Now you have to start adjusting your glaze’s rheology with deflocculants like darvan (sodium silicate can and will make it worse). The material is cheap, but you pay more in time trying to fix problems and in wasted work. It’s more economic to use other sources of boron like gerstley borate or frits. Many boron frits are still soluble, but a lot less than borax. That said, if you’re knocking together something like raku glazes that will be used the same day, borax could be a a good teaching material.

90% of the time un-sticking tactics for me involve filling a need that I’ve been neglecting. Is it my mind, body or spirit that needs attention? Do I need to rein in my caffeine consumption so I can get some sleep, do I need to get out of my head and go visit friends, or do I need some time to sit and noodle over a problem? Do I need a new playlist or audiobook? Am I hungry? Mostly getting unstuck is some form of “go away and do something else for a while so your unconscious can work on it.”I don’t love everything Julia Cameron does in her Artist’s Way books. I don’t think that treating a creative block as a pathology or an inner child is necessarily the best, but the parts of her approach that involve treating yourself gently and giving yourself mental/emotional space and time are good general life advice. Creativity is play. You have to feel safe and warm and fed, and a little curious and a bit bored in order to begin to play. If one or any of those elements are missing, you have to do whatever it is that will get you into that state.

Just because my son was working on statistics math* earlier: Adding 12% clay shrinkage to your estimated final size isn’t the same is a piece shrinking 12%. It doesn’t usually matter a lot when you’re making relatively small items like this, but the slight difference can be a nuisance if you were, say, trying to throw a 20 oz mug that fits a silicone travel lid. 12% of 10 cm (for easy math purposes) is 1.2 cm. So if a 10 cm cylinder shrinks 12%, it’s now 8.8 cm tall. But if you start with an 8.8 cm cylinder and add 12% to that, 12% of 8.8 is 1.056 and you wind up with 9.856cm. It’s not a lot, and likely won’t mess with volume measurements at this scale, but it’s enough to mess with lid fit. The difference gets more significant with larger shrinkage percentages and larger dimensions. If you want to end up with a 10 cm cylinder and your clay shrinks 12%, then 10 cm is 88% of whatever the starting point is. So you divide 10 cm by .88 to get 11.36 (rounded) cm. *Yes, I used pottery shrinkage as a real life example for why he needed to learn this.

I don’t think anyone here is going to tell you not to worry at all ever, or call you a liar about your body’s reactions to things. I think we try and advocate for the right amount of worry, and if you have sensitivities, you DO have more to pay attention to. IN GENERAL, *if* you don’t have preexisting medical conditions or risk factors, you shouldn’t develop mould problems from the stuff in clay. Most of the stuff we work with can cause irritations like coughing or abrasion related contact dermatitis, but not usually assorted immune responses such as raised histamine levels or anaphylaxis. The original poster on this thread didn’t indicate any prior issues with mould toxicity, so we were addressing the question from that standpoint. As many have already mentioned, your own body and the specific mould generating the mycotoxins you’re reacting to are the big deciding factors. If you are allergic to one of the bacteria or moulds in clay, then continuing clay work may or may not be advisable. It’s the ever occurring answer to anything in clay: it depends. The information on mould toxicity I’ve seen indicates that sensitivities and reactions to mould depend on exposure levels, frequency, and a wide host of other possibilities including your physiology and the specific bacteria/mycotoxin. It’s not impossible for clay bucket cultures to cause issues, but there are other more likely sources like your food, gum disease, or a contaminated home/workplace. If you’re going out to clay class once a week, your exposure is going to be a lot less than if you work everyday in your humid basement studio that is never mopped. Good studio hygiene will also limit exposure. It’s possible for long term exposure to cause issues, but the research also shows it’s possible for some to develop resistances or even for the problems to resolve. (Denice just chimed in with exactly that happening as I’m typing this.) I have to stress that no one here is a doctor, and we can’t give you specific medical advice. Even if someone is a doctor, it’s illegal for a medical professional to do so publicly on the internet. If you’ve got specifics, you definitely need to consult with your medical provider. If they’ve been doing their due diligence and looking after you properly, they should have all of your history and be able to take your circumstances into account.

@Tforkpeople usually use boiling water, or take some of the glaze water, add the crystals to it and microwave it a bunch. It does take a bit of time from all reports. @moonariif you check the MSDS sheet for the glaze, it'll give you some vague information, but it should be enough to see if there’s lithium or boron/calcium.

Most of the folks I’ve seen do any kind of Mishima technique usually trim the surface of their pots. I’m thinking of MIchael Klein’s IG videos where he’s scraping white Mishima slip off of the pot’s surface to reveal the patterns below. I’ve also got a Katy Djreiber wax Mishima mug that feels like the surface was probably scraped with a metal rib or other trimming tool, or maybe even wet sanded after the bisque. So it might not be that the shrinkage of your clay and UG or slip need to be matched perfectly, it could be that the extra scraping/compressing levelling step is key to getting the surface flush.

Sitting down and trying to answer this one feels like trying to answer the chicken vs egg question. Because this question came out of a thread asking how clay has shaped you and I come from a position of finding clay in my formative years, I’m trying to tease out in my own head if there a disposition that leads you to clay, or does working with clay creates some kind of disposition. I think given enough time, it’s a bit of both. This one is really make me chew on how to put my thoughts into words. I’m going to have to think about it a bit and come back!

Products that are sold specifically as washing soda usually have other ingredients added to them that will really mess with your glaze bucket, so it might not be the end of the world. Can you get your hands on some Dispex from any of the places you get materials from? Because that would be the ideal stuff for the job, and a little goes a long way. Even if someone has to bring a 1l bottle in their checked bag, it’ll last you a looooong time.

How much of any given deflocculant you use depends on what else is in the clay body and what consistency you want to arrive at. If there’s any solubles in your clay/glaze/engobe, that will affect things. Although if there’s solubles, you usually don’t need a deflocculant. My suggestion would be to make a saturated solution of soda ash (say that 5 times fast!), and add it in tiny quantities, mixing for several minutes between additions until you get your desired results.

If you want to be able to insert a metal rod into the sculpture, the softer the clay is, the easier it will be. If you’re thinking of using something like a long electrician’s drill bit to do this with, a firm leather hard stage would be ideal. You want the spot where the clay won’t stick to itself anymore, but is still wet enough to absorb vibrational stress. If the clay is bone dry already and if the piece has precarious points, your clay body may not withstand this approach however. At that point, drilling the bisque out is probably less likely to cause spalling or chipping, or even small pieces breaking. If you have to bisque the piece, follow all the advice about preheats and going slowly that would apply.

If your wareboards are moulding while you’re using them, you might be covering your pieces for too long. If you have to leave your pieces covered due to time constraints, put the plastic under the piece so the moisture isn’t getting to your plywood. It’ll also help to slow the drying down. If you can get back to your piece and finish it in good time, you might be wrapping it too tightly.

It sounds like you’re using commercial dry mix, correct? The only thing to be mindful about storing glazes outdoors in the heat is evaporation. Check your consistency and maybe measure your SG before each glazing session to make sure the consistency is where you want it. This should be done anyways, but life does happen. More issues happen with cold. I had an unheated garage studio for a long time. Freezing glazes isn’t the end of the world, but it does make dipping glazes hard pan. You can rescue them, just be prepared for it to take a while, and you’ll absolutely need to re-sieve. As long as the plastic container they’re in is still flexible and there’s room for ice expansion, even those will survive. Continued cold under the freezing mark can make plastics brittle, but I think that’s not going to be an issue for you in San Francisco Bay Area. A note about the article that Peter linked: if you have some solubles in your glaze, you might want to be more mindful of the temperature if you aren’t using your glaze for months at a time. You can tell if your glaze has solubles if the water that rises to the top of the bucket is not clear. If the temperature gets to about 15*c (59F) or lower, over the course of a month or so, glazes with either soluble boron and calcium, or lithium can start to form assorted solids. The lithium ones will be flat-ish, and have an octagonal or hexagonal shape. Those can be re-dissolved in hot water and added back into your glaze so you’re not changing any chemistry. Boron/calcium ones will be little round guys. I have yet to find a method of re-dissolving them. If you’ve only got a few of the borocalcium ones, they can be discarded without too much damage, but be sure to use up the full batch before adding any more ingredients to your bucket. If you remove too many, you can affect your glaze’s chemistry.

What I mean by firing for my clay body is that instead of trying to finesse the glaze, I bisque with an eye towards a clean burn off: slow and thorough, and as Min mentioned, paying attention to a couple of specific zones. I also will go slowly in the first part of my glaze fire (up to about 700C) just to hedge bets. I fire my particular clay body hotter than the manufacturer recommends because otherwise it doesn’t meet my porosity standards. Rather than firing to a higher temperature, but I do a drop and hold schedule and let heat work push the cones over so my clay doesn’t bloat. I started doing all of this because I was trying to get a clear glaze to actually look clear over a red clay body. The clear I was using looked great over white clay bodies and I had no problems with it even over the darkest underglazes, but I was having a heck of a time with micro bubbles over just the red clay. I’d already tweaked glaze recipe and application problems, so I started doing all the firing adjustments above. In the process I noticed that it improved the appearance of my other glazes, and gave me more consistent results all around. Some helpful links are this digitalfire article on pinholing, and this video/article from an industrial ceramics site. Note that the last one assumes that the reader is working in an industrial setting, and adjusting the firing cycle is one of the least practical solutions. Because we’re working on a much smaller scale than that, the firing cycle is one of the first things we can look at. The digitalfire article is a good starting point for troubleshooting, and has lots of links to other helpful stuff. You’ve already gone through a bunch of it, but there are some other things it mentions, and digitalfire is a good resource to know about in any case.

I do a bunch of work that involves combining a red clay and white slip, and what I’ve found is that when you apply it and how much water is in the slip does make a big difference in how well the 2 stick to each other. But my white clay has a lot less flux in it than yours does. I also found that firing for my clay body solved a huge boatload of glaze problems. My inclination would be to try 3 things and see what works best. The first two are adding more opacifier to your homebrew white, and doing a bit of a line blend with your most recent iteration of the original engobe, decreasing the frit 3110 in increments of 2%. I think what’s happening is that the engobe is melting early enough that it’s keeping your clay body from being able to offgas properly, leaving some residuals that are still trying to break loose in the glaze. Despite what they used to tell us years ago, colouring oxides do have an effect on the melt, and cobalt and copper both get moving kinda early, slowing down the release of those residuals. Iron is also melting, but it can also act as a fining agent, and it releases bubbles more readily. A third suggestion would be to slow your bisque down, and let it soak without pushing any cones over. That should allow further off-gassing without changing the porosity of your bisque. I don’t know if you have access to a machine like a Cricut, but if you make your stencils out of reusable vinyl, it could make them more “dip friendly.” Or maybe spraying the backs with some kind of adhesive or starch before applying them.

@Up in Smoke Pottery and @Marcia Selsor have both been contributors to the forum in the past, although it’s been a while since I’ve seen either of them chime in. Tagging in case they’re lurking. Marcia is probably one of the foremost obvara artists in North America, and if you get no love from any of the links here, I’d suggest reaching out to her via her website for some clarification points.

I’ll sell seconds, but only in person so that there’s full disclosure and people can make informed decisions. Second criteria is anything that’s got cosmetic issues, but does not interfere with use, is structural, or that could possibly scratch a human or any of their belongings even slightly.

I think there will always be people that ghost us, especially if they’re contacting via electronic means. I try to give folks pricing, terms and conditions before I start digging pieces out to take pictures of them to send. It can help weed out tire kickers. I also pointedly ask people to let me know how they want to proceed, so I’m not hanging out in limbo. There’s not a lot of tone in emails, so you have to go to direct communication tactics, rather than implied.

I have found with red or other dark clays, a slow speed is just as good, if not better than raising the bisque temperature. It will depend a bit on your clay body. I don’t notice a huge difference between 06 and 04 bisque in the clay I use, but a slower bisque makes a noticeable difference.

Vinegar only kills some bacteria that don’t survive in an acidic environment. It’s a poor germicide. It will also flocculate some glazes, which will affect how it brushes. A tiny pinch of copper, which many potters have on hand already, or even some peroxide is better.

Glaze pinholes aren’t caused by organic additives to the glaze burning out. When we talk about organic burnout being a possible cause of pinholing, it’s from the carbonates/sulfates etc that are chemically bonded to the glaze materials themselves. Things like CMC, glaze additives and wax are gone and vented out of the kiln before anything starts to happen on a ceramic level. So, I don’t think you have concerns there. As far as whether or not wheat dextrin will work to help stick the glaze to the pot or make it more brushable, it’s always worth an experiment in the name of science. As always, do a test with a small amount before adding it to a larger batch, and don’t use it on something that’s precious until you’re confident in how it'll turn out.

Or just go on long walks. Makes sense. According to my ceramic history class, a lot of Roman era potting in Europe was a seasonal, part time gig. You did it when you weren’t busy farming, and there’d be time to source and prepare materials in advance.

If it was only the big flat things, then the most likely fix is to add a foot rim. It’s still a good idea to do some porosity testing on that clay/glaze combo. If the clay isn’t mature, you could have issues if you want to be able to put pieces in the dishwasher or microwave. Digitalfire has some good tutorials on how to. https://digitalfire.com/test/shab

+1 for peroxide. Tiny quantities of copper carbonate will also kill mould and bacteria without affecting the colour of the slip. It’s often used as a preservative for gum solutions.

A friend of mine who runs a paint your own pottery place uses Stroke and Coat for their underglaze colours, but she also covers all the pieces with a clear coat of glaze. Stroke and Coats can be a little on the dry/stiff side sometimes, and a zinc free clear glaze can help with that. The colours tend to be very stable, so if all you want is more gloss, that could be a very easy fix.

So, the valence of the metal can make a difference in your glaze’s outcome, yes, but the degree that it happens to depends on the material, and sometimes the other ingredients in glaze recipe. Mostly, the oxygen or carbon atoms that are attached to the familiar colourants burn off, and aren’t part of the finished glaze at all. The purity of the source of the material will sometimes affect your outcome, and different valences of a colourant may melt differently which can also affect some glazes. Recipe substitutions are possible in many cases without having to first change black iron oxide into red iron oxide though, if that’s what you mean. From a glaze calculation standpoint, the important thing to know is how many atoms are being supplied to the recipe by a given ingredient, and you can make substitutions if needed. For instance, you can substitute black iron oxide (Fe3O4) for red iron oxide (Fe203) in a recipe. You’ll need to weigh out less black iron to get the same effect. You can also substitute red or black copper oxide for copper carbonate. In the case of cobalt, the carbonate form supplies fewer cobalt ions to the mix, but both are powerful colourants and even small amounts of the carbonate form will give you a dark blue colour. If you aren’t familiar with glazy.org, its a website that offers free glaze calculation software. If you want to figure out how much nickel powder you’d need to add instead of nickel oxide, you can plug your original glaze recipe in and tweak the numbers so they’re close before you begin real life testing. It saves a lot of time.