kristinanoel

So glad you solved this problem! I had it a while back, mine was also a sieving problem. In looking for the cause, I also came across this great post that talked about the importance of blending. Enjoy! https://glazy.org/posts/173081

congrats! and I agree with BAM2015, a steady $1k a month is nothing to sneeze at!

@Kelly in AK how does this preform for ware boards wrt drying? is it like drying things on a plaster bat? I've been running into drying problems with plates on bats made of plastic and masonite - plastic keeps the base wet and i get cracks when the lip drys faster than the foot, masonite warps and I get a wobble. If this acts like plaster, seems like it could be a really nice solution!

@Ryan Greene I'm intrigued by this sand wadding technique - I agree with everyone that this does seem to be happening in the cooling phase, and you're spot on, I also think it's a shelf/air problem where the sides are cooling much faster than the rest of the piece. How does one do the silica sand wadding? As for the glaze - yep, I mix it myself, no lithium, and I've used this glaze/clay combo on other forms, even low plate forms (albeit smaller and with less height, so no fast cooling sides to worry about) without any problem, so I'm thinking it's that irregular cooling problem. If my mitigation tactics don't solve the issue, I'll likely finish out this order and then abandon this glaze on this form! @Callie Beller Diesel well, no talc in this one, so that's something! how does the new talc behave - does it encourage crazing/crackling? pinholes? introduce any other problems? I've got another recipe that does have talc, haven't used it in a while, but would be good to know.

@neilestrick Ah ha! The slow cool schedules I found do seem more aimed at achieving glaze effects than addressing cracks - Would a natural cool to 1100, followed by a 150/hr ramp to 1000 make sense?

@Bill Kielb true - that's a risk I'm willing to take for the design. While I don't have pieces that are decades old yet, I've been making this style for about 3 years and this is the first time I've ever seen this kind of shattering, either immediately or with time. And I even throw these things into the dishwasher with no problems to date. I'm planning to do a full round of troubleshooting test fires, trying out: refinishing the kiln shelves firing with silica sand during glaze firing with waster slab slow cooling - looks like a rate of 150/hour down t0 about 1600 sounds like a place to start keep those peepholes CLOSED! skip the vent fan (maybe can re-introduce after I've figured out the problem) Thanks to everyone for all the generosity - any more ideas are welcome!

More great lines of inquiry - thank you all. @Roberta12thank you! I love this glaze. There is actually no glaze on the exterior, which is my normal way of making, so no change there. @Min can I break one - absolutely. they're already broken! Here's one, I'd say this is on the thinner side for me, but well within the normal range of thickness. as for the break - it' sharp, in some cases it's not even separated, just obviously fractured, and it happened all up and down my kiln. I fired 9 of these. 8 of them fractured. I did have a vent fan going, which I do not use consistently so that could be a problem, although I've not noticed it causing such trouble in the past. I think i will eliminate that variable, however, and just stop using the noisy thing entirely. @Rae Reich oh, peepholes for cooling, yes, I have done this forever, it hasn't been a problem before but that doesn't mean it's not one now! great suggestion. At what temperature do we consider it safe to remove peepholes? I generally don't crack the lid before 500 degrees, and then only if i'm in a hurry, but I usually DO remove peepholes early, I never knew that was a problem. Something else to eliminate. @Babs I usually crack the kiln between 400 - 500 degrees if i need to get it going again soon, otherwise i wait till i can touch everything, about 150. I do not remember what temp i opened this kiln, but either scenario would have been normal for me.

@Pres excellent point. I've had trouble with the center slumping, which is why I've resorted to foam support. Perhaps I am inverting too quickly. I should perhaps more consistently cover the rim and leave the center open, something I do periodically, so that the center dries enough to invert without slumping but without overdrying the rim. Thanks for the input!

@neilestrick can waster slabs be reused? and do you use the waster in both the bisque and glaze firings? If I don't have alumnia wax, would a little bit of silica sand do the same thing?

Thanks so much for these suggestions! @Bill Kielb Kiln shelves! - I think that may be the culprit. Your explanation makes perfect sense and aligns with what I'm seeing - the way the stress fractures appear leads me to believe that there's some form of stress being introduced after the drying and trimming are complete, so in the bisque fire. I DID scrape, sand, and re-wash my kiln shelves prior to this effort, and the wash has been persnickety, flaking off and generally acting poorly. I've also not done the silica protocol, but will try that in the future. Thank you so much. @JohnnyK Not super old - less than a year and stored in my cool, damp basement. I've had no problems with other forms, albeit slightly smaller (plates, smaller forms of this bowl) but I will contact them to see if there are any known issues. That would be a bummer, what a waste of $$$$! @Pres thanks for this - I don't think the glaze thickness is a problem in this instance, it's certainly not even close to the thickness of the base, but the relative thickness of the rim to the base is always an issue, I've always had slightly thicker bases than the perfect ideal, but I've never seen this error rate! And your suggestions are spot on - I already practice all of them but the boxing of the forms, so I'll try that. And a question - when I invert the forms for drying, I usually support them from the interior with foam, is that your practice as well? Any cons that I'm not aware of on that? Any other ideas? Keep 'em coming! Of course, this lesson learned has to happen on a 'big to me' order with a lot of pressure to get it right. Totally failed, have had to miss the deadline, ask for an extension. When you hear people recount stories of "failure and resilience", it's usually from the after position, when they've made a comeback. I'm here to tell you that in the midst of it, man is it painful. I have a much greater appreciation for the Icarus story. Thank you all again for rushing to the rescue. I sincerely appreciate it.

Hi friends - I'm having a new (to me) problem I can't figure out, something is causing my ware to fracture in the glaze fire. I'm assuming it's from tiny, undetectable fractures, but not sure what's going on - I've been making these low shallow bowls for a while now with no major issues, and nothing has changed, so I'm stumped. I used to have problems with S cracks which I addressed through better compression but these seem different. Have you had/solved this problem before? What's the diagnosis? More importantly, what's the cure? I'm using aardvark obsidian, I bisque to 04 using the suggested firing schedule. The clay felt fine when throwing, perhaps a little stiff but not abnormally so, it's never been frozen/thawed, and it's fresh from the bag, not reclaim. Thanks in advance! Kristina

Thanks! The container - i'm thinking of that as a big low, flat tray, like an open top sagar, a sandbox, essentially, just to contain the silica for easier cleanup. Like a kiln shelf with a raised lip?

Does anyone use a deeper bed of silica as a support for sculptural pieces, to prevent slumping? So that the ware is kind of nested in a pile of silica, or in container? I've heard of this but not seen any images and not sure how it would work. Can the silica be re-used?

Min - do you happen to have a photo of what you're describing? I'm having trouble picturing it but would like to try it out.

Late to the party but I say rutile - I call it 'interesting powder', with RIO a close second.