Kelly in AK

I appreciate this question. As well as the notion that simple frit and clay glazes are best . In the 2016 paper, Matt refers back to the 2012 presentation, discussing results of 0.5 R20:0.5 RO samples in relation to boron. He concludes that paragraph with: “Thus the quality of glazes is not dependent on any specific temperature for durability. Chemistry is the only relevant factor.” Obviously, temperature does matter, if a glaze hasn’t melted it’s not complete. But once it has fully melted, why would a glaze that’s durable at cone 04 (say, 0.3 R2O:0.7 RO, 0.5 boron) be less durable if fired to cone 6? It might run all over, but that’s a different problem.

Definitely will smoke!

Calcining clay only has to get to around 1200° F, if that helps. Tony Hansen has some good info on it if you haven’t already seen: https://digitalfire.com/glossary/calcination

I use cement board for multiple things: wedging, ware boards, and working on. As a work surface I have to get it wet or my clay dries out too fast.

I saw Tom Coleman sift alumina on his kiln shelves. He said his porcelain would sometimes pluck (fuse) if he didn’t take that step. I had the thought of painting kiln wash thinly on pieces of newsprint and layering that between your porcelain sheets. It’s an idea, not sure how practical it’d be.

Thank you for the photos. I believe you made the pots too thick. The outside profile vs. the inside shape shows it, to me, clearly. If the bowl is in fact 20” wide, the foot must be well over an inch thick in some areas. There are many variables (relative humidity, clay body, temperature of candle, etc.), an eight hour candle ought to have taken care of most of them, but honestly it’s just too thick and blew up. Water did that.

We’re hearing a lot in the news about silicosis because people in the “cultured stone” business, countertops, are getting it long before a lifetime of exposure. This is a really specific scenario though. These people are cutting silica slabs all day with inadequate protection. The exposure is hard to fathom. That’s not to mention the unknowns about the engineered material they’re working with. You shouldn’t worry about this. You’re doing the right things now. Even if you had a few dusty years you didn’t ruin yourself, not even close. Keep the dust down, wear a mask when you’re playing with powders, you’re good.

If that’s the glaze, then wiping across the emblem with a sponge may do it. I’m with @neilestrick on stamped food surfaces. Do it on the bottom or find a glaze that fills it and still shows the details. I like that stamp. Nice looking work!

My BFA professor was a sculptor, her work was around 4-5 feet tall and probably averaged an inch thick. She used an Imco sulpture clay, it was pretty groggy. Also fired very slowly. Another thing I've seen is people building reinforcing structure inside the sculpture, extra walls where support is needed.

This is cool. You can have your own clay mine, with pool! You’ll hardly have to leave the house.

Thank you Mark, that explains it very well. A wide combination of factors creates the variation in price.

I was rearranging my glaze materials, making space, trying to cull out stuff I never use, and I came across twenty pounds of lithium carbonate. Something I don’t use, which is why I forgot I had it. So much talk about how expensive it’s gotten made me wonder enough to look up what it actually costs, you know… just in case. Now I’m totally confused. Prices from ceramic suppliers, some I’ve ordered from and some I haven’t but are well known, are all over the place. They ranged from $50 to $130 a pound. Does anyone know how much lithium carbonate costs?

I use two clay bodies, one for cone 6 soda firing and the other is a local clay that fires at cone 03. The cone 6 body is Laguna B-mix 5. After trying various clays I found it responds well to soda as well as hot and cool spots in my kiln. It seems easy to throw for me and is pretty tolerant when my craftsmanship isn’t perfect. The downside is it’s expensive compared to other white stonewares. The local clay is something I’ve played with for many years and gotten to know. It isn’t tolerant in any way! I add 1-1/2% Veegum to it, the biggest monetary expense. It cracks, slumps in hot spots, and is left porous in cool spots. I have to be completely on my game to make it work, which is part of its charm. I haven’t tried to calculate the cost, I’m afraid it would be too discouraging.

Off the cuff, if you have a chimney, use it.You'll need a blower/sucker to shunt gasses from the kiln to your existing stack. Long horizontal runs are bad, all exit pipes should have some insulation to keep that column of air hot until it’s free of the buiding. Flapper valves on your building exterior are effective in establishing a one way street.. If you have a downdraft (electric ) vent it may be more economical to just run that straight out the wall. you definitely want to vent your kinl.

You fixed it after bisque, when you fired it again, what cone was that to? The tension causing the crack doesn’t go away, it’s set up when you’re making the work. Firing exacerbates it. Bisque firing, a little bit, higher firing, a lot. A lot of tension makes a bigger crack. At cone 6 (or whatever your clay matures at) there are massive changes in chemistry and shrinkage. The two big shrinks are wet to bone dry and bisque to glaze, if you’re firing to vitrify the clay. Bisque shrinkage is negligible, but enough to expose hairlines that will greatly expand upon maturity in glaze firing. Post photos and you’ll likely get a solution to avoiding the crack in the first place. You’re in a community of crack doctors. Or at least a crack perseverant population.

@Pyewackette I looked back at my post, it was a late night just-before-bed ramble and did go on and on a bit. I think I may have missed making a clear point in all of it. I didn’t mean to come across as dismissive and apologize if that was my tone. I can’t think of a way to differentiate the dangerous coloring oxides from the safe ones. They’re all very specific in their risks. For example, I think of cobalt as risky because it’s so damn hard to see until it’s high fired. I could have it on my fingers without a clue while eating fried chicken. Two percent or five percent in a glaze bucket looks about the same. Iron’s not like that. You absolutely see it. The two I can think of that pose virtually no risk are iron and zircon. The only way I understand to mitigate all chances of toxicity is either to lock the colorants in a glass that will not degrade under the most extreme conditions or put them underneath a layer of that glass. If you put too much of a colorant in glaze it’s not the metallic oxide that makes things dangerous per se, it’s that you weakened the glass enough to allow it to degrade and leach that metal. Encapsulated stains are arguably less likely to leach their coloring oxides, but thankfully their ingredients are published and you can choose the way you use them. There was a time (Not so long ago!) when leaded frits were argued to be safe beyond reproach. That’s just to say, I respect where you’re coming from. To go further, barium and lithium aren’t coloring oxides, but used as fluxes and adjuncts to color, yet have known toxic properties. But there I go again. Too many commas in one sentence. I gotta go to sleep! Nailing down what’s dangerous is tricky, I believe we all want to do that. It’s a journey. Stay away from lead.

Just a country boy here… What do colorants do in a good hard (stable) glass? Stable meaning it is durable, resistant to both acid and alkali, and smooth enough microscopically to not grind away forks and spoons (cutlery markings). “Welcome to ceramics… again.” A phrase I repeat to myself as I learn new things I thought I knew well. If you have a strong well functioning clear liner glaze that is durable through acid (lemon juice/vinegar) and alkali (many dishwasher cycles), stays shiny, and fits your clay, then you've arrived. Zircopax will make the glaze tougher, not unlike alumina, and whiter/more opaque. No additional toxicity. Iron will alter the color and, depending on the %, temperature, and atmosphere will, produce a great variety of effects. No additional toxicity there either. Chrome, copper, cobalt, manganese, and others rely on the hard durable glass to keep them locked in the matrix. Personally I keep those below 2%. Your worries about Mason stains are in the same vein, except encapsulated Mason stains are designed to be non leaching in nearly all circumstances. If you aren’t confident in how good, hard, or stable your base glaze is, no rules of thumb will help. It is not beyond your ability to find or compose a stable glaze and that should top your to-do list. Another line of thinking is to put all color underneath a stable glass, as in slips or underglazes. The foolproof option. No matter what, none of the materials we ordinarily play with holds a candle to lead in terms of toxicity. Our biggest toxic risk is mixing the glazes carelessly.

My approach is to get everything wet that I can without ruining it, flood the floor, then squeegee it outside. It took a lot of effort to arrive at baseline we felt comfortable with. Since then it’s regular (weekly) passes with a HEPA shop vac, high and low, with the garage door open. Followed by flooding the floor and squeegeeing it all out or down the floor drain if it’s mostly water. When weather doesn’t permit the open garage door it’s an n-95 canister mask till the job’s done.

With the gas kilns it’s all me, and that’s been a long slow learning curve. It started with “don’t blow yourself up.” My experience with electric kilns is a different. I count on electricians. However…I learned, as many do, electricians in general are unfamiliar with kilns. If you find one who is into kilns, they’re a gem! I’ve learned enough to do a lot work myself, but I’m not yet confident to flip any switches till a pro checks it over. Except the thermocouple. I don’t need a pro for that.

I’ll throw this out. The worst/best/most dramatic fuming effects I’ve seen were chrome and tin. The tin glazed white pot is now pink on one side because the one next to it had a chrome wash. Next is copper, in reduction at least, pots near the pot with high percentages of copper in the glaze, um, may be affected. Sometimes a red splash is provident, others it’s the ruin of a pot. Cobalt is insidious. Practically invisible until fired good and hot. Then it’s the blue that just doesn’t quit. I haven’t had so much a “fuming” problem as a “How did that get there?” problem with cobalt. Soluble metallic salts? No thank you. I prefer most metals in a non soluble form. Except sodium.

20” x 20!” Large tiles indeed. No mean feat in my book, 12 or 18 hundred degrees, you’ve passed some hurdles. If I had two sets of tile from one body, one set being fired to 1200°F and the other fired to 1800°F I believe I could tell pretty easily which was which. So, yes, imagine you could too. As mentioned above, get it wet. Try to dig in or scratch it. Properly fired bisque ought not yield to that with a fingernail or wooden tool. A metal tool (steel) can scratch soft bisque with effort, but I’m getting more specific than I intended. You might ask me about what’s proper, then I’d be in trouble. If handed a piece of bisque ware and asked what temperature it was fired at, I’d have to ask a lot more questions before I ventured a guess. Be careful with those tiles, glad you fixed your settings. It’s a blip. Oh yeah, cones! Use those until you have no reason to wonder what your kiln is doing. And again when you do have reason.

I rely on sanding the foot (after glaze firing) to take care of this. I do polish with the wooden part of my tool when trimming, but that alone doesn’t do it. And if a pot warps in drying I’ll slide it around on a wet ware board to flatten the foot, which pretty much ruins that burnished surface. 220 grit to knock the sharp edges off followed by a quick 600 or 800 wet sanding to polish it a bit. It’s not too involved, a brief operation on a pot by pot basis. My feeling is if I can slide the pot on a tablecloth without any snagging it’s done.

Words from mages: Fewer pulls, Tend your pulls towards the the final shape. Be aware of the architecture of an arch, how it supports what’s beneath. As little fussing as possible. Work dry as you can. Good luck.. Heat guns are aggressive. Takes some finesse to not crack things. Embrace trimming.

I appreciate the updates on this @Hulk, I made a few bats of Hardibacker for my partner about a year ago but she hasn’t used them yet! My wheel doesn’t have holes for bat pins so I haven’t bothered to try them either (I’m accustomed to using roofing felt bats). We both regularly use it for ware boards though. The belt sander is a worthwhile step.

Nice!!!