Kelly in AK

Pretty clear you’re need an outdoor solution. It’s likely to solve more problems than it creates. An enclosure is doable, not rocket science. You will need good casters and a very smooth surface to roll that kiln. Kiln fires in open air, is retreated to its kennel/shelter when cool. With enough space around it elaborate leaf catching schemes may not be necessary. A hose is necessary. It’s gotta stay out of the weather when not in use.

The soda kiln gets vacuumed every firing. There’s plenty of stuff flying around in there, I don’t need anything extra to ruin my pots (While I’m at it, shelves get scraped and lightly washed every time as well. Silicon carbide shelves.). Electric kiln, very seldom. Once a year. Glazes get sieved when I see chunks while glazing. Some glazes do form agglomerations. When the glaze dries and there’s little bits sticking up, that’s my sign. Those bits don’t always dissolve into the melt.

On another side note, verging into off topic territory, yet not, is the copper red crackle that can happen on re-firing. I didn’t take pictures of my own pots this happened with, but I assure you from experience it happens. Crazed copper red glaze can go red in the craze lines. I believe reduction cooling or “strike firing” is a purposeful way to make it happen. I found a picture from Christie’s auction house that shows it.

Re-firing to bisque temperatures won’t stress your work with cone 5/6 clay. You will be loading and unloading it one more time, which is a slight risk. The only risk I see in glazing over unfired underglaze is screwing up the glazing to a point you have to wipe it off. Underglaze has ingredients (gum) that harden it on drying, it’s pretty robust in terms of applying glaze without smearing or bleeding. Especially if you’re dipping to glaze.

You run a higher risk of having blisters or pinholes unless you re-bisque to the temperature you know works.

Neil, you kind of beat me to this, but since I already wrote it... Minnesota Clay's website says the range of MB6 is cones 6-9. At cone 6 they say it's "vitreous and porcelain like." Also at cone 6 the absorption is listed as 3.7%. Huh? At cone 9 absorption is 2.1%. Their cone 10 version "MB Stoneware," lists absorption of that body at cone 8 as 1.4%. Yeah, the high fire clay is more vitreous at cone 8 than the mid range clay at cone 9. Something funky there. Back on topic: The studio head, if they are mixing glazes, uses a recipe. Ask them for a copy. If they are using premixed dry glaze you should be able to learn the supplier and the supplier will have some data on the glaze, though they don't often share formulas. It's possible with a recipe to adjust expansion of a glaze to fit a clay body (not always, but generally). This clay body though, I'm not so sure about it. Doesn't look "mid range" at all on paper. I do have issues with suppliers who bill clay as mature over a span of four cones, but I'll stop the rant here. Asking this question directly to the folks at Minnesota Clay would probably be the most direct solution. I suggest, however, you get some clay that is actually vitreous at cone 6 if you're making functional pots in that range.

I second the veegum, you have to hydrate it in advance though. Not something you should add dry.

My steps are much the same as others have mentioned, with one exception. After soda firing all the wads have to come off. They mostly fall off easy, sometimes they need a little persuasion. The next step is to scrub any residue of wadding off using a Scotch Brite pad under running water. Only after that do I consider what has to be sanded or ground. That scrubby pad takes off a surprising amount of material and gets into little divots. All feet get at least a once over with wet sandpaper (320 or 400 grit) so they wont scratch your great aunt's grand piano.

I dug up “John’s Noxema,” it’s from John Britt’s book The Complete Guide to Mid Range Glazes. Some similarities, some differences. Lots of feldspar, but soda not potash. No wollastonite or Gerstley borate, rather strontium and 3134. An abundance of cobalt, for sure. Kona F-4 spar 50 Frit 3134 24 EPK 11 Strontium carb 11 Silica 4 Add: Cobalt carb 3 Bentonite 2

I expect people more knowledgeable than me will check in, but for my initial reaction, I suggest you’ll want to look into various boron based frits. They will give you some modicum of certainty, that is at least one of your glaze ingredients can be depended on to be exactly what the analysis says it is. You’ll get the boron content you need to flux things at cone6. I lean heavily on Ferro frits 3124 and 3134, but the are several others you can use to tune your glazes with specificity. As to blue at cone 6 my thought was including an opacifier (zircopax, tin) would help even things out and reduce that “breaking” quality. That’s just a guess. I have used a glaze from John Britt called “John’s Noxema” that fired very evenly. I didn’t like it for exactly the reason you might seek it: it didn’t break enough on edges and texture.

I visited David MacDonald’s studio in Syracuse last summer, he said if there was one thing he could change it would be to get in-floor heat. With forced air it’s a constant battle to keep his giant platters from warping. The drain in my floor is a lifesaver for cleanup.

Outlet/venting for the kiln is tied for first with plumbing a utility sink. Once those two are settled, other things find their place. Clay is close to the door with wedging table nearby. Glaze and all my lovely powders are near the sink. Once it’s exactly how I want it, I’ll tweak it for for a few months and probably rearrange everything. Next I will somehow run out of space. Haha! I’ve learned enough about myself to know that anything that can be put on wheels should be (Locking casters, I’m in an earthquake zone).

I’m sorry to see what you’re going through. It’s one of the worst things, after getting everything right every step of the way, the last move blows the lot. Other than seconding advice already given and offering encouragement, I’ll say what I would be looking at if I were there (note: been at it a while, still learning) The decal firing is just above quartz inversion, a nice clear clue. The clay is not liking it. Perhaps it’s a rushed firing cycle, but there’s clearly some tension in that clay/glaze going on. I wouldn’t hesitate to do a test on a piece that survived: put in ice water, take it out and pour boiling water in. Half full, you want to stress it. It just takes a few minutes and one way or another, this test brings great peace. In addition to the suggestions already mentioned, consider using a different clay for the large platters or maybe glaze firing them slightly lower. I’ve had a few bad dunting days myself. Note in the attached photo most shattered pieces are one glaze (the red one) and also flat, plates and trays.

Wonderful!!! I’m thinking over how things have evolved in my classroom and anything I wish I knew sooner. Ware boards, places to wedge clay, and efficient processes to recycle clay top my list. Rolling carts (so much easier to move 50 pieces by rolling them right where you need to). A pug mill is worth its weight in gold when you’ve got 100 kids producing scraps all day. Vacuum pugger/mixer is the dream. Just got one last year after 15 years teaching clay and it’s “all that.”

First guess is two or more layers of different colored slips/underglazes on textured porcelain, then scraped, followed by sanding after bisque to really clean it up. Whatever she’s doing it’s marvelous.

Probably absorption is my number one concern, followed by how it looks after soda firing. Generally, if something works I stick with it but occasionally try new things. Laguna's B-mix 5 is working well, I fire to cone 6 or slightly hotter and it gets very tight. It does warp if taken too high. And it's more expensive than I would like, but it really works well in soda.

Good to know, this (also from Tony Hansen) may be more directly relevant: https://insight-live.com/insight/share.php?z=jDCvHWKF6P Good luck!

Speaking in the most general terms here, the easiest fix is to apply the glaze very thin and/or fire it slightly higher. It’s not really fixing the problem though. As Pres mentioned, it would help to know the temp you’re firing to. Many people on this forum fire to cone 6, but those recipes look like they melt well below that (I’m assuming 3134 in the first recipe is 30%). It’s not an uncommon problem, but can involve several variables. Tony Hansen has published some excellent work on this, freely available. For starters you could look here: https://www.digitalfire.com/glossary/transparent+glazes

It reminds me of a glaze known as “water blue” that uses copper carb. Some versions have strontium and lithium, some don’t.

If the bottom is particularly thin that may also have some bearing on the problem. Again to reference Hamer and Hamer’s book, the section on crack diagnosis is outstanding.

In Hamer and Hamer’s “Potters Dictionary of Materials and Techniques” there is a diagram of a crack, labeled “crack f” that looks very similar to your picture. The causes the list for this crack in glazed ware mostly have to do with a mismatched COE. One particular note mentions glaze that is thick in relation to the bottom of a piece, the action of the glaze fluxes the clay of the bottom more than elsewhere. I read that as having to do with the thinness of the bottom as much as thickness of the glaze.

Thanks for reporting back! I’ve used that same primer and it’s tough stuff.

Mosquito larvae enhanced the plasticity. (Just kidding. Don’t try it.)

At school I occasionally end up with a few different clay bodies for the students. Sometimes other schools will give away clay that’s too stiff to use, since I have a pug mill I always get as much as I can. After fifteen years doing it, the biggest problem remains the “other stuff” that sneaks into the reclaim bucket. The pugger mixes everything into a homogeneous body and it all starts as cone 5/6 clay. There was a year I got some porcelain and that required a few trips through the machine to get it mixed in well (didn’t have a pugger-mixer at the time, just a simple pugmill).

Since you caught me right after I mixed up a bunch of glazes and tests, my shopping list starts with a digital scale! The leftover money goes to Veegum.