Kelly in AK

In my soda kiln (c6), it both gets hotter on top and cools more slowly there. Selsor’s Temmoku is almost always matt on my top shelves and glossy down low. It’s not because they’re under fired. The slow cool is the obvious variable in my case. I believe the high percentage of iron has an effect, because other glazes using the same base don’t behave that way.

Magical cone 6-10 rated clay creates many problems while solving only one: You don’t know which clay to pick, so you choose all-in-one. (You can imagine where I stand on this). Okay, two- the kiln master now has no worries about melted pots in c10 firing. Until someone offers proof that a clay body can be vitreous (<2% absorption from c.6 to c.10), and not suffer from excessive warping or bloating in its stated upper range, and not suffer from glaze defects related to outgassing in its lower range, I’ll be calling BS on the “wide firing range” bodies. They have applications, but they’re specialized. I strongly agree with @Dick White, that clay will be off gassing at various rates the whole time from bisque to six. The bisque firing will not eliminate that. Some glazes will handle it well, others, not so much. A drop and hold/soak schedule might solve it. Still, at the lower range of your clay you may have some pots that leak. Check the “absorption data” from the clay seller.

Sounds like an “equipment and repair” thread.

I like big mugs and I cannot lie.

One is a Brad Shweiger. got lucky at NCECA cup sale. The other is unexpected luster in my own kiln.

My guess is that the clay has a lot of organic material in it. Anaerobic bacteria, explains the clear rind, the depth oxygen can penetrate. My experience : When paper towels get in the slop bucket it makes a black zone. Perhaps the clay you use has an organic plasticizer added. It would be worth checking (with your seller), because it sounds like the whole batch, not just pockets are reacting. I have no solution though, just a possible “why.”

Unglazed work is not a problem in any way, it has to do with what you want it to look like. Chilly mentioned that earthenware and bisque are basically identical temperature ranges. If you’re new to ceramics, understand that people can be technical without realizing they’re speaking a different language. All parties walk away thinking they communicated when they did not. Bisque essentially is earthenware, and would require no separate firing, so I’m wondering if by “earthenware” you mean something else. You could be thinking of unglazed stoneware. I think this comes down to the clay you’re using. Clays are rated by temperature (and other ways, such as plasticity and shrinkage). The three common ranges are cone 06-04, cone 5-7, and cone 9-11. Clay undergoes a change in its character when fired to maturity (its cone rating).

My companion is my studio mate. She doesn’t complain, unless her favorite glazes are running low.

One more thing, bricks are not pots. Stuff that would disqualify a clay for pottery may not for bricks. You’re looking for enough clay to hold it together, and it to stay together until it’s fired. Additions of fibrous material are common to brick making. Critical for adobe blocks. Aggregates much too large for pottery clay are also common in brick clay. Plasticity is a wholly different issue for potters than brick makers. Your first tasks: 1. Can it be formed into a brick? 2. What are its fired characteristics at various cones?

There was a brick plant in Anchorage in the 1950s, briefly. They used clay straight from the ground and ran it through a large pug mill. Fired them clamp style. The working and firing properties of the clay were known, and lots of testing for structural integrity and freeze/thaw resistance were done. The engineering tests of finished bricks will be critical if you’re using them for a structure. You’ve got some work to do well before figuring out how to make them en masse. See if you can make a couple dozen to completion, that will give you a lot of useful information. The Cardew reference is excellent.

I can only turn this over in my mind, I have little experience with underglazes, a fair amount with very low fire (016-012). I used to do a lot of terra sigillata and burnished work. I feel like I understand what you’re after, you explained it well. A matte surface that retains the kind of saturated color a glaze has. (Your work is beautiful by the way) So my thoughts are on silica and alumina. Silica is a glass former, yes, but also very refractory. There is a point in glazes where too much begins to matt the surface because it can’t melt in. It’s also clear, kinda, at least less than opaque. I wonder if actually increasing the silica would be something to play with. The other idea being about alumina, and increasing that (and silica) by adding a small amount of terra sigillata made from a light burning clay (OM4 was my first thought, it makes a very nice sig, but perhaps a kaolin). In my head the problem is to get everything to barely begin fusing, enough bring the colors out of that pale chalky phase, without going into full melt. The fine particles of terra sig begin fusing before their parent clays do. Just some musings.

Some raw materials are increasing more than others. All of them are increasing. Watch lithium bearing materials like spodumene and hectorite. Crazy. That means any premixed glaze will cost more. Different suppliers have different prices because they buy In quantity, sometimes they buy a ton of something well in advance and can make a profit selling it lower than market price. Do some shopping, it’s a temporary fix. Everything is going up. Avoid buying water (liquid glaze), add your own.

I second @Mark C.’s comment. I don’t think you can fire your way out of this one, I believe you shouldn’t even consider it. You said it’s problematic on the stoneware “clays,” which leads me to think it’s more a glaze issue than one odd clay body. There’s a lot of talc, probably gives you the satin, but very low expansion. I’m not a glaze expert, so can’t advise in depth that way. My only advice is to respect this principle: If a combo is shivering, pieces that haven’t shivered just haven’t done it yet. Doom the lot. Edit: After pronouncing doom I figured I’d better consult my “bible,” which is Pioneer Pottery by Michael Cardew, because I recalled it as the chief source of my principle. Digging through the section on glazes I did not find satisfaction, then discovered he talks about shivering at length in the section on clay bodies. From around pages 64-75. Not exactly as I remembered, and Cardew treats it more specifically as a clay body issue than a glaze fault. He also talks about different manifestations of the the same problem, such as “shattering” and spiral cracks. Good reading for clay nerds. Good luck and, as Mark said, there are lots of white glazes out there!

Left hand holds the tool, right hand is touching left as well as the tool closer to the blade, backing it up. I didn’t learn to rest my fingers on the pot, so I rarely do. In the last five years I started doing a thing I saw Simon Leach do- put a few drops of water on the wheelhead, center your pot, push down a bit, and trim. If you’ve used the right amount of water it’ll stay put through trimming. It takes a few tries to get the hang of, but I almost never use wads anymore. Brilliant for bowls. One of these days I’m going to learn to tap center. One of these days.

Olsen’s kiln book, Rhodes’ kiln book, 21st century kilns, all valuable. You’ll find slight variations in principles of design from each source, that’s why I think you should check them all out. Unfortunately I’ve never been able to get my hands on a copy of Nils Lou’s book, but it’s been highly recommended over the years. I’ve got one of those neighborhood kilns, a cross draft flat top, propane and wood soda fire. Cone 6. I would suggest that while it is possible to build a wood burning kiln where smoke is not an issue, such a thing is unlikely to happen without a great deal of planning and experience. I’ve seen several wood kilns in action and built a few myself. To get the combination of reduction and temperature rise some black smoke is going to happen. I’ve never put a blower anywhere on the kiln, maybe that’s the trick. I ended up going from mostly wood and a little propane to mostly propane and a little wood, because I didn’t like worrying that someone was going to call the fire department every time I did a firing. Getting to temperature in a day with wood wasn’t ever a problem. So I strongly agree, firing with wood does not have to be a drawn out affair. Big firebox, a grate, big chimney, proper design of entrance and exit flues. Ash buildup can be increased by stirring around the ash pit often (it starts sticking to pots earlier than people imagine, around bisque temperatures), if you like. Soda and controlling the reduction gives me the flashing and textural variations I’m after though.

For pottery clay I imagine salt would at least have some negative consequences in firing. I, for one, have not tried it. Watching fluid quick-clay suddenly become solid with the addition of salt is dramatic. The chemistry teacher at my school has done it with our local clay. It’s a pretty complex phenomenon, the salt leaches out (over a geologic period of time) and leaves the sedimented structure like a microscopic house of cards. When that’s loaded with enough water the slightest disturbance breaks it loose and everything flows. Particle size plays a role too, the layers and proportions of clay, silt, and sand affect what areas become “sensitive.” Reading through some of the research after the 1964 Alaska earthquake suggested to me that there were areas of clay on top of, below, and adjacent to what liquefied that held together. My experience trying various proportions of clay:silt surprised me most by how they dewatered on a plaster slab. The purest clay dewatered slowly, like ball clay. Silty clay that was smooth and moldable (but poorly plastic) dewatered in minutes. Weirdly, I’ve made pots of it that begin to dry so fast because the water is flowing through them as they sit, the ware board just sucks it out. I really have to use my imagination to try and understand it, and probably have no business trying to explain it, but I can say for certain what’s worked best for me. I try to pick clay as far above sea level as I can find it because I want as much soluble salt leached out as possible. It’s ultimately about getting the most clayey stuff though. The more clay is in the material, the harder it is to break apart in my hands, if I whack it, I look for conchoidal fractures. If I can break it and crumble it to dust, no matter how much it feels like clay when it’s wet, it’s got too much silt. I guess I’m going on at length here because that one little distinction made such a difference for me. More than any additives or adjustments to processing, my best clay starts with careful picking. Always looking for the motherlode.

I didn’t try vinegar, but did use 0.2% epsom salts for a while. It made a noticeable improvement, nothing like the Veegum though.

My local clay Anchorage, Alaska, has been compared to Norwegian quick clay. Blue-gray, fires red, is thixotropic. It occurs in lenses with silt which looks identical. I’ve found that I have to be careful to not get too much silt. I sieve the stuff to about 60-80 mesh, but the silt easily passes through. Too much silt and it’s definitely more thixotropic, has very poor green strength, and splits easily. Even when I have processed high quality clay I still add 1-2% Veegum.

Yeah, the different types of plastic have different “permeability” ratings. Even though they’re all waterproof. Fun fact, Mylar is as close to zero as you can get which is one reason they make balloons out it. I’ve certainly noticed it with clay I’ve bagged up for storage.

Just checked on Veegum, last time I bought was right before the pandemic hit, it was around $10/pound. Now it's nearly $30!

Another Alaskan, nice! Make sure your electrical system can handle the kiln too. Looks like that one needs a pretty big breaker.

After it’s thrown, then: 1. Flip it over, 2. Trim, 3. Terra Sigillata (since that’s 2-3 coats, it’s actually two or three times I handle each piece at this stage), 4. Load in kiln, 5. Unload, 6. Glaze, 7. Load, 8. Unload, 9. Pack Occasionally, some extras: Adding handles, sanding or clean up of finished work.

I transport greenware regularly, usually bone dry. No doubt it would be less fragile leather hard. I use copious amounts of bubble wrap.

Two wild Alaskan beasts. They’d rather be pulling a sled, but sleeping while we make pots seems ok with them too. As you can see, one prefers hard cold concrete to cushy carpet.

Well, it’s good to know, apparently some decals can be persistent to cone 6. I haven’t done decals, so my thoughts are conjecture (based on knowledge and experience, mind you!). The first and only thing I could think of to mend these was some wet-or-dry sandpaper. I know it comes in as low as 400 grit, which would be better for removing material than the higher grits. Decals are only skin deep and fired on at low temps. They’re probably a lot softer than the glaze. I’ve certainly removed the outermost layer of a cone 6 glaze with wet sandpaper. Still, x28 is a lot. They’ll all have to be glaze fired again to heal the scuffing. The idea of an etching paste is great, that could cut down on the labor quite a bit even if it didn’t remove all parts of the decals.