Kelly in AK

I’m no glaze wizard, but I’ll throw in my impressions (worth 2 cents, not a penny more). It’s such a “fluxy” glaze recipe, I really can’t imagine how it could be so stiff and matt, especially with all that Gerstley borate. I do wonder how it behaves in the bucket, Gerstley being prone to gel and help suspend non plastic ingredients. If the bentonite was so overloaded it seems you would have noticed something funky when you mixed it. I feel like you didn’t miss the spodumene, that’s contributing to the brown-ness. Edit: After a good night’s sleep I do remember seeing a picture of bentonite fired near maturity on Tony Hansen’s site. Very brown.

Thank you so much Tom, as always, I value your insight and advice. My clay produces excellent terra sig, in good volume compared to other clays I’ve made it with. That, in my mind, correlates with a significant amount of ultra fine particles, though I know there are other factors involved in how deflocculated clay settles out “Cones” made from the clay tests is brilliant.

My clay body, local Anchorage clay, has its faults that I’ve been working to mitigate over the years: Narrowing in on particle size distribution, exploring additives, playing with firing schedules. I’ve made a lot of progress, but there’s a variable I haven’t taken head on yet. That is optimum firing temperatures. Right now my best results are 98% clay, 2% Veegum. That makes it play like pottery clay. A little extra attention to attachments and bottoms prevent predictable shrinkage cracks. For both forming and firing stability I tried Lincoln 60 at 20% which helped in the forming part, but only changed the firing range imperceptibly. I’d like to get a full cone of useable range in the kiln, right now it seems a hair’s breadth between 04 and 03 will produce vitreous pots. A regular 04 gives me 5% absorption, a solid 03 and things begin to slump, higher still and they dunt and bloat. Between those two are pots with1% or less absorption. Tough as nails, and ring like a bell. Would adding kaolin, a nice alumina rich clay, be a reasonable tack to explore?

@Callie Beller Diesel creep is a materials engineering term that refers to materials exposed to stress deforming over time. We’re doing some accelerated action in a kiln, it might be likened to pyroplastic deformation (I’m no engineer, but I play one in this forum). An example of creep, though there are probably less obscure ones, is Frank Lloyd Wright’s historic house “Fallingwater.” His plans for the cantilevered concrete slabs showed they were to be cast with a reverse camber, to compensate for natural creep of the concrete. In my crude sense, it means to cast them curving up a bit because in time they’ll tend to curve down, even though we think of concrete as an absolutely rigid material. They were instead cast flat, and over many years began to droop, then crack, requiring great expense to remediate the historic building. Of course in a kiln this all happens in minutes and hours, not years. Our rigid material shows exactly where it would “creep” under the force of gravity by warping and slumping.

I was thinking of firing shrinkage rather than creep. I just looked more closely at your setter design and realized I saw it wrong. I imagined there was a cylindrical projection on top that isn’t actually there. The principle behind my thought still holds though, clay will shrink in firing and if it’s shrinking “onto” your setter that’s a possible crack. If it’s shrinking “away from” the setter that stress isn’t set up.

Pardon me if this has been addressed. Clay on the outside of the form will shrink on and crack, left to its own devices. Clay on the inside will shrink away from the mold and survive. Clay fired on the outside of a sitter has a similar risk if tolerances haven’t been calculated.

Woohoo! AI is no match for us. The thing that gets me is the hemispherical cross section of a rowing scull. I can’t imagine how you guys manage not to tip over. It’s the most unstable hull shape one could possibly create. The fastest, apparently too, but always looks like walking a tightrope to me.

Highly likely. It’s all coming from the same pit, even though a year apart.

Shut everything down and unbricked the door as fast as I could. There’s a strange kind of panic when you think your phone is cooking. It’s a new feeling. Sure enough it was cooking. When it was cool enough to handle I peeled off the melted gooey case and of course tried to turn it on. Half the screen was gray, the other half looked like nothing happened. I was able to plug it into the computer and back it up, which seemed like a miracle, another new feeling. I went and got a new phone, and all was well with the world. I also ran an extension cord and lamp to the kiln. Makes me smile every time I think about it. What a dork! Haha!

It’s likely they do, very characteristic of the clay body. The surface skins over quickly when I roll slabs. The ones at the bottom are those kinds of cracks magnified from bending the clay.

Ok, the question’s been out here a while, but I just remembered an epic screwup that makes me laugh and had to share. Not the worst , but probably the funniest. I was loading my kiln, it’s outdoors and dark, so I turned on the flashlight on my phone and propped it up on the bagwall. Finished loading, got the door bricked up, lit the burners and reached for my phone to take a picture. Where’s my phone? Oh noooo!!!

I believe what Neil suggested about organics just burning off about the time the kiln shut off could explain it. It ran for about three hours, so seems to line up for me. We don’t often see in the kiln from 500-1000° because it’s dark and why would you? That’s what it looks like though, especially in an unvented kiln. It’s that the smell was “different” that raises alarm. And yet, just as Neil said, there could have been something foreign in the kiln burning.

“The artist I want to be…” Love that.

This is not my wheelhouse, however since I’ve personally had a kiln malfunction in an unexpected way I feel compelled to mention this: Have you taken the outlet cover off to see how things look in the junction box? I do suppose you have because you mentioned the wiring size, and if you mentioned doing it specifically I apologize for being redundant. An electrical smell is what it is. The nose knows. Mine was a hardwired kiln with a junction box that was too small, overheated and caused the wires to short. Kiln, control box, all fine. Everything happened in the wall. (Wired by a licensed electrician, by the way!)

I want to thank everyone for their ideas and critical thinking on this. I appreciate it. Again, it’s not something I’m going for, just something that happened and I wondered about. Yeah, it’s not a snowflake thing. I was hoping for an explanation where I didn’t have to imagine too much. But you’re right @Min, the copper and zircopax don’t support that and furthermore it’s not applied thick at all. But it is uneven. I pour glaze in, then out, rotating the piece. It produces an area that’s thicker on the pour side. There’s also a leading edge to the pour that produces a distinct difference in thickness. Then I dip the rim. It’s all very fluid and organic, but there’s some complexity I hadn’t thought of. Considering thickness is one variable for a copper red glaze, well, there’s a lot of variation in thickness here. My current thinking is in firing the glaze cracks on the way up, like in glazes that crawl, just not so extreme. The shape and size of cracks are determined in part by the thickness of the glaze. I reduce for around 30 minutes starting at 012, before the it begins to fuse. Those cracks create separate plates of glaze and based on thickness, reduction affects each one individually. As the glaze melts they fuse back together. I reduction cool it to 1500° and that reliably produces reds for me, even if I fire a neutral atmosphere the whole time. Not sure how it fits, I just have a hunch it plays a role. Here’s a different glaze doing not the same thing, but I believe something related.

@Min, definitely true and a very important point! What I said only applies in the most general sense.

Haha! @Hulk you beat me to it! (What he said^) Unfortunately most of those things designed for room temperature will completely burn away in the firing. Also, I’m not sure how helpful I can be, because I have no idea of the realities of buying ceramic supplies in Scotland. I can at least give you something to go on. Apologies if I’m giving you information you already know. As for oxides/carbonates, there are relatively few that are commonly used in studio pottery, Iron oxide being the most common, inexpensive, least toxic, and easily available. Copper carbonate, manganese dioxide, cobalt carbonate, tin oxide, and chrome oxide, are some others that come to mind. In other words, you won’t need to hunt down every metallic oxide known to man but if you do use oxides your color palette will be limited. That said, I would suggest most ceramic experimenters (probably most potters, to be honest) prefer using Mason stains for coloring both slip and glaze. Mason is a brand name of ceramic stains and, while I have no interest in promoting them, they are reliable, used worldwide in industry and private studios. “What you see is what you get” after firing, which can’t be said for oxides.

They’re mostly variations of 3134+3124+clay, then some coloring oxides and/or zircopax. The white liner I use is (% analysis) Na2O 6.11, K2O 0.81. A glaze that behaves similarly to the one I originally posted (I haven’t seen the odd fractured color patterns in this one…yet) has Na2O 5.03, K2O 1.45. Now, a caveat with those numbers is an ingredient in both glazes is my local clay. I use the generic term “red clay” as a substitute ingredient in Glazy, so I don’t really know how accurate the analysis is. A third glaze I’ve used that has no local clay in it comes out at Na2O 6.34, K2O 0.35

Yep. I think that nails it!

I attended a weeklong workshop with Josh DeWeese (not too long ago). I’ve seen a lot of demos. I’ve done a lot of demos. I never imagined I would stay so engaged watching someone else make work. Being in his company was quite a delight, left an impression.

Thank you for that article @PeterH, copper red is fun and fickle and I’m no better at understanding it after all these years. I can usually manage to get it nowadays though. I gave a shot to trying to get some better photos, but the mojo wasn’t with me and they’re no better than what I posted. When I have a few minutes to play with the camera I’ll try to oblige. @Min, it’s exactly what I first thought of when I saw it, big snowflake glaze. On another note, some of the reds I get are very much at the surface. It’s the reduction cooling. They make it through the dishwasher fine, but they’ll scuff right off with a light sanding.

They were on the bottom shelf of a downdraft kiln. The trickiest place to get a good reduction (in my kiln, anyway). Babs, when I figure out how to do this on purpose you’ll get first pick. Thank you for the compliment.

Yes Peter, definitely cracks. They’ve melted together, some on the rim are filled with glaze showing as red lines on the mottled background. And, to note, the pieces rang like a bell out of the kiln. They’re in my cupboard, not in the “for sale” pile. The smaller ones still ring, this one (cereal bowl) now has that dull thud that means its days are numbered.

It’s a single glaze @Babs, poured in and out, then the rim dipped. What gets me isn’t the color change, that’s not a surprise. It’s the angular nature of it. I do suppose it’s got something to do with varying thickness of the glaze.

I’ve been pondering this one a while, I had a few pots do this a year or two ago and it’s always puzzled me. I’m not after repeating it, I’ve evolved the glaze into something different, but it still fascinates me. If I ever wanted to chase this I would have no idea how to think about it. The glaze was: Frit 3134- 50 Frit 3124- 30 OM4 - 20 add 10% zircopax, 3% copper carbonate It’s fired to cone 03 and reduction cooled to 1500° F (propane). It usually goes all red, but in some parts of the kiln stays blue- green. Not unexpected. The way it changes color here in such distinct places surprised me. If anyone has thoughts or explanations I’m delighted to hear them.