Callie Beller Diesel

So I actually just did a round of simulated dishwasher/acid testing on the 50:30:20 base glaze, but with some tin, RIO and rutile added (the combo is really ugly, so I don’t recommend them). It did pass both tests. But the colourants may also play a part in the flux ratio, according to the Katz research. (I’m not willing to throw that out entirely. I think we just don’t know all the modifiers on it yet.) As far as practical applications, it does appear to behave well in the bucket, doesn’t run unduly, although keep an eye on the thickness. It does react with other glazes reasonably well. My version is pretty expensive because of the tin, but even just the base glaze is a steeper cost than the base glaze we’re using at the teaching studio I’m at now. It’s not out of control, but the base runs $7.25/KG (Canadian dollars) and with 4% tin it’s $12.05/kg.

As long as the early segments of the firing go slowly enough through the applicable temperature zones for burnout, you should be ok for sawdust inclusions. If the kiln is a relatively large one, the sheer thermal mass of everything *may* take care of that. Consult with the owner of the kiln to see if they have proportion suggestions. Another possibility for inorganic inclusions could be crushed shells, if you have access. They’re calcium, so they’ll leave small white voids that may crumble away in any unglazed dry areas. In terms of making flashing slips, look at any “dirty” kaolins you may have access to. If they’ve got titanium or iron impurities, they could do interesting things.

Any container going into your next bisque will work. I wouldn’t trust commercial terracotta, just on the basis you don’t know what temp it’ll melt at for sure.

Ok, everyone has to cheer for my IG friend Renu! (You don’t, but I will be. She’s the sweetest person, and she’s the art teacher that everyone has super fond memories of.)

After checking this article from digitalfire, it looks like actual Cornish stone stopped being available in 2014 or so, but there are a number of substitutes. So it’ll be worth checking into which substitute this is before deciding on long term availability. Some of those substitutes were made by combining other feldspars and if Custer was one of the ingredients, that could still present a problem. In general, Cornwall stone isn’t as strong a melter as feldspar, and a straight 1:1 substitution isn’t going to work well at cone 6. You might need to add a bit more frit, or adjust with a touch of neph sye, depending. Cornwall stone also has some phosphorous in it, which can make for some neat colour responses/reactions. But it can also flocculate your glaze. Because I think you’re likely not looking for potassium to provide a specific colour response, you could try subbing another feldspar that has a combined sodium and potassium number that’s closer to Custer’s combined values (KNa). The silica and alumina numbers will be less important to match in your substitution candidate, as you can adjust silica or EPK numbers in this recipe to compensate.

I won’t give too many people heck for making a long post! I’m often guilty of novel writing myself. (Case in point!) I think if you’re finding the tool unwieldy, it might be too much tool. I agree that you may be overcomplicating things with the spreadsheet and in keeping the photos after the project is done. Especially if you’re in the hobbyist/community studio stage of the game. You only need to collect analytics that are useful on the regular: I promise you don’t need to collect the bisque weight, except for a couple of specific tests. Unless your studio needs this information for some reason, I have no idea why you’d need to collect trimmed and bisque dimensions. If you’re tracking them for personal growth, that can be done elsewhere. I use Trello for my personal benefit in the moment, not for keeping a permanent document of everything I’ve ever made. I leave my workflow board undated, and archive or delete cards after I’ve pulled an items started count at the end of the year. Square collects an itemized list of pieces sold as well as sales metrics for me, and photo documentation lives in my photo files. I don’t know too many small scale potters (under 75-100k revenue) who need a full inventory system/workflow software integration. But if you love a good spreadsheet, there might be a power up or an ifttt (if this then that) integration that might work. I think that’s more for folks like East Fork, and they’re probably paying for purpose built software. I also found that filling out every last field on the cards is a nuisance, so I created a few card “templates” that I can just copy when I need to start a new batch of a regular stock item. I then just have to add start dates and the number I need, and the colour. I also don’t keep images of finished pieces on the cards. I usually only add an image of a design sketch, if necessary, and delete when I’m done with the project for the reasons you cite. I don’t use it for materials inventory at all.

Sanbao studios has some nice ones. They’re at chinaclayart.com

I was schooled in the 90’s, so my teachers were working in the 70’s. As awful as their habits were, the only one of them that died of cancer had one that wasn’t silica related. The conditions I’ve read about that caused silicosis in the developed world involved construction sandblasters who were working long hours every day, and exposed to huge amounts of dust due to the wrong respirator and inadequate ventilation. Unless you’re doing something very wrong, i don’t think your studio looks like the inside of a dust cloud. I say this with love and gentle humour: you probably are being neurotic. The purpose of going to the doctor at this point is for them to reassure you better than we can here, but also to get a documented baseline for lung function. It’s one of those sensible precaution things, and it isn’t urgent.

Heads up that the Pacer mine, Custer’s producer, has gone bankrupt with very little notice to its customers this month. So if you’re looking for ongoing use of this glaze, it might be wise to get ahold of some Mahavir if you don’t have any. You may have to adjust this recipe with a hair more epk if you use that one. If it’s just a matter of using up Custer you already own, it might be a bit less fluid than G200, but it’s a closer match than Minspar.

Your initial assumption about the majority of people who wind up with silicosis being in much more industrial settings than yours is correct. There’s a lot more documentation of silicosis with miners, or sandblasters. I won’t say it doesn’t happen to studio potters, because I try not to make absolute statements like that. But I have yet to hear of a case of someone I know with it, either online or in person. I think a few 3 Kg batches of glaze and some sweeping aren’t going to do you in next few years. That’s not to say you shouldn’t employ good studio hygiene going forward, though. If you’ve got other medical things going on, like allergies, asthma, pneumonia that gave you lung scarring, long covid, etc, the addition of silica and other dust isn’t going to make your day better. It’ll add irritation on top of those things, if nothing else. If you’ve got concerns, you should definitely bring them up to your doctor. +1 for Mark’s lung diffusion test. I’m having my GP do similar with me.

I do have practical knowledge of this. It’s wise to back up shells with other wadding for structural support, especially when tumble stacking, placing large ware, or other instances where the load may shift. The remaining calcium is pretty hard immediately after firing, but if the shell itself was thin, there’s only so much structural load it can take. So size and shape of the proposed bone is something to consider. The Simon Levin article makes mention of his neighbour using cow bone sliced on a bandsaw, but something like poultry bones might not work as well on their own, being smaller and much less dense. According to the digitalfire bone ash page, the frit softening point, which will be affected by the fact that it’s pulverized, is 1670*C/3038*F. So unless the bone comes into contact with ash or other fluxes, I can’t see it melting or fusing to things it isn’t supposed to. You could get some interesting flashing from using bone that other wadding options might not offer. Bone ash is used in some high fire iron reds, which is another interesting connection.

+1 for taking a class or joining a group studio, especially if you’re looking for a hobby. In addition to all the reasons listed above, you will be around other people who are excited about clay, and the community in these scenarios really accelerates your learning.

Another trick is to blow sharply onto the fluid glaze immediately after dipping. You’ll get some glaze in the imprint, but not so much the letters get filled in. I’d show a picture of the results, but I do this on my swear word mugs.

From your image, the bubbles look like they’re still trapped under the glaze somewhat, or have barely popped and haven’t healed over. In this case, I support getting a little more heat work into your glaze fire at the end, whether it’s going half a cone hotter or a drop and hold. Depending on the mechanism used to achieve a matte, some of them can either be a bit more refractory, or they’re just a bit less viscous than gloss recipes.

Your saturated epsom salt solution is dissolved. Your glaze is a suspension*. Dissolved is not the same as suspended. Dissolved is like when you make a simple sugar syrup or saline: the sugar or salt particles become indistinct from the liquid. A suspension is when the particles stay distinct from the liquid it’s in, but stay more or less dispersed throughout. A suspension may settle out over time, or be re-suspended when you stir it up. A solution won’t loose the original materials out of it, unless it changes temperature or some of the water evaporates out of it. *a glaze can sometimes be a combination of a suspension and a solution if some of the materials do actually dissolve into the water of the glaze over time. The boron in things like gerstley borate or some frits are known for being soluble in glaze buckets, as are a few other things. This process tends to take a few days or even weeks, and when it happens, the now-solution part of the glaze helps keep the other dry particles suspended. This is also called gelling or flocculating. When you add epsom salt solution to a glaze bucket, you’re either creating this effect in a glaze that has no (or negligible) soluble materials, or accelerating it in a recipe that has some solubles. Unless your glaze has turned to the consistency of something like skyr or Greek yogurt, you have not ruined it with the amount of epsom salt solution you've added. Single cream is kinda sorta the ballpark of what you want a glaze consistency to start at, but you’re still having some settling. Your description of your glaze’s behaviour with the epsom salt says you might need to add more. But there’s some question about the amount you’ve already added. Is your epsom salt solution super saturated, or did you dissolve some in some hot water and go from there? A super saturated solution is made by adding Epsom to boiling water from the kettle until you can’t dissolve any more. You will need a surprising amount for this. There should be some crystals at the bottom of the container that won’t dissolve easily while still hot, and as the solution cools, some more crystals should appear at the bottom. The resulting solution will be clear, but will refract light in an almost oily way. It’ll also eat through metal lids over time, so if your storage jar has a metal lid, line it with a bit of cling film. If your solution isn’t super saturated, that could account for the seemingly large volume not giving you the desired effect. If that’s the case, you do have some room to add more. You also have to mix quite thoroughly to give the effect a chance to work. A cautious method to test if adding more would help or go too far is to remove a sample from the bucket and add flocculant to it by drops, mixing well between additions.

Don’t get too hung up on specific SG numbers. The number that works is the one that gets the right application of glaze YOU want on your pot, and that might be different than what someone else recommends. The 1.4 mark is a rough starting point, kind of like seasonings in a recipe. Some people will want more, some people will want less. First, water is the easiest thing to adjust in a glaze, and adding things like epsom or darvan to adjust how a glaze flows should be done only after you’ve determined it’s really necessary for getting the right glaze application. If the bucket has a layer of glaze materials in the bottom within 5 minutes of mixing, pulling out the epsom salt solution is the right thing to do. Adding epsom salts will flocculate a glaze, or make it gel slightly. This is why the glaze now seems thicker than it did, and it may leave a more generous layer on the pot than the same 3 second dip would without the flocculation. You might notice on some glazes it will start to crack while drying, potentially causing crawling in the kiln. And yes, it will also slow your drying time. That slowed drying can help smooth out application based drip marks. If your glaze is one that might be subject to crawling due to application, adding water will help resolve that. But know that adding water to a glaze that’s already flocculated will further delay drying. It may mean you have to adjust your workflow to allow for that, but it’s worth it if it means the glaze goes on the pot nicely. Another question worth asking is whether or not any of your ingredients are soluble in the bucket over time. It’s usually more of a problem with boron containing materials, but some feldspars can be subject to this as well. Solubles can affect glaze application if they cause additional gelling.

A lemon test won’t rule anything in as safe, but it will rule out things that are susceptible to acid. That said, alumina isn’t a super volatile material in ceramics, and generally* adds to the durability of a glaze. It’s pretty refractory. That said, if it’s a dry, powdery lump of kiln wash sticking out of the glaze, that’s not good for craftsmanship or aesthetic concerns. You could try glazing over it and re-firing. Even if the alumina was not bonded and someone ate out of this piece, you also have to consider whether there’s enough material there to do damage to anyone. I’m not saying you should leave kiln wash bits embedded in your piece. I say that only to contextualize potential risks. *assuming the rest of your materials are also within reasonable parameters, and the glaze isn’t already an alumina matte, which would be a logical assumption in a liner glaze.

Trudy Golley taught this technique something like 25 years ago. While you can slipcast into paper plaster moulds, as Jeff mentions it does wind up having uneven absorbtion because of the pulp distribution. She used them primarily as slump/hump moulds for handbuilding, and they are indeed a lot lighter. Because you’re sculpting the mould, you can do things like put feet on them to make them easier to handle, and you don’t need cottle boards. Or have to worry about said cottle boards failing mid pour. As I recall, mix both the skim coat and sculpted layer according to standard plaster ratios, and simply add the paper pulp (or she used cellulose attic insulation) that has been wetted and wrung out. She recommended the attic insulation because it had preservatives and fire retardants that hold up a lot better than toilet paper would. Newsprint pulp does work, but you have to dry the resulting mould thoroughly. Note: you do NOT want to use the fibreglass blow in insulation. It has to be the cellulose kind.

Clarification on the Glazy post: the image of that glaze on White Bear clay isn’t Joe’s, it’s another contributor using that glaze. The accreditation is in the gallery. Her name is Michelle Smith. https://glazy.org/u/mlsmithsbcglobalnet/recipes

Don’t discount the Stroke and Coat. While they’re technically a glaze, it behaves like an underglaze that happens to go glossy. It’s quite stiff, and if you don’t cover it with a suitable clear at earthenware temps, it can show raised brush lines. They’re smooth at cone 6. I have not found them to be translucent at all. I have a friend who runs a paint your own pottery place, and they use them as underglazes, with a coat of clear over top. They don’t run or blur.

If you run a bit of 220 grit wet/dry carbide sandpaper (I get mine at Canadian Tire), it should take off stubborn alumina remnants. If you feel fancy, you can tack some to a bat and make a quick and dirty polishing wheel.

I was told that another part of the reason for the small cones deforming later is that they have the weight from the kiln sitter arm applied to them, where self supporting and regular cones don’t. So the later melt is to help compensate for that, as they’re being used as a shutoff.

The vent systems for electric kilns here mostly involve a 10 cm(ish) hole in either the roof or wall, similar to what a clothes dryer uses. Plus ducting, mesh to keep animals out, a suitable fan and a sheet metal hood that funnels fumes either from the top of the kiln or draws them out through the bottom. So they’re very doable in a situation like you’ve described.

The only reference to density and zinc I could find was a brief mention on digitalfire about there being 2 different processes that can be used to derive zinc oxide, one of which creates a denser product. But the same article mentions that zinc oxide is one of the purest materials we deal with, so I would think that as long as the recipe is using weight and not volume measurements any substitutions would be chemically the same. That said, the density may affect other working properties. If the zinc is in the recipe as one flux among several it will matter less than if it’s something like a crystalline glaze.

With the caveat that my kiln does not have a digital controller that would be much more subject to temperature variations, yes, I am proof you can easily run a kiln at 0 C. Mine is in a metal shed outside. The kiln does start to struggle a bit at -30 C, and at that point I can’t blame it. We don’t get those temperatures for more than a week or so in most years, and they tend to come at times where I can easily wait to fire. The power consumption doesn’t go up measurably: 20*C difference in temperature matters to human comfort, but not to a kiln. It’s not uncommon where I live for potters have kilns in their garages, which are typically unheated and are often uninsulated. A digitally controlled kiln will need to have a temperature reading from the thermocouple of 0 C before it will turn on, and what many do will put a small space heater inside the kiln to warm the area before they begin loading. Once the kiln is generating its own heat, it’s usually fine. Ventillation is another matter. Even with an electric kiln, you will want to make sure it’s vented properly. As the different minerals loose organic components, those carbonates and sulfates will need to go somewhere, and that shouldn’t be into your home, never mind where you sleep. In North America they sell kiln vent kits for the purpose, but you should check with whoever sells you the kiln about locally available equivalents. The only time I’ve seen gas kilns indoors was in institutional settings, where the building was purpose built and incorporated a LOT of venting. Otherwise they should be outdoors, but sheltered from the elements. They emit everything an electric kiln does, plus combustion, plus presumably some incomplete combustion for reduction.