Callie Beller Diesel

@oldlady, I will add a few tags to this post so it’ll show up in search.

Can confirm that is black coring. A fast glaze cycle isn’t great for bisquing most clay bodies, red ones in particular. I think that this is pretty strong evidence for going too fast through quartz inversion and excess free silica being your cracking source. If you look through the digitalfire articles, especially the ones on black coring, bloating and clay testing, you’ll find a lot of really helpful info on how to proceed. There’s a really interesting note in the black coring article with some observations about red clays and feldspars making strong high fire stonewares. This could be a really nice clay to add to a clay body to give it some character. It seems to need some feldspar.

Refiring cone 6 items usually gets tricky when the underfired piece got close to the intended temperature range the first round. Accumulated heat work is going to matter less if the pieces only got to bisque temps.

Babs makes a good point. If you haven’t made this piece, I wouldn’t attempt it. You don’t know what temperature the clay or glaze matures at. If you don’t know exactly what glaze was used, the one you apply could create a eutectic with the existing glaze, making both run a lot more than they would by themselves. If the piece was originally fired at cone 6, refiring it to low fire temperatures may partially re-melt the existing glaze, making it do all kinds of ugly things.

Regarding the overall response here: we’ve had a LOT of folks over the past few years ask about how to achieve a similar aesthetic as in the pictures you’ve posted. Most beginners don’t realize the look can either achieved with photography edits by someone who is both a good potter and photographer, or with poorly fired/impractical ware made by someone who is taking accurate pictures. Without holding the pots in question, it can be hard to spot the difference. When someone doesn’t know badly fired ware is a possibility, they have no reason to think to look. Glazes that are dry matte can be made through a number of mechanisms, some of which are great for sculptural work, but aren’t durable enough long term to use on kitchen dishes. However some glazes that have a satin finish are extremely durable and ideal for functional use. You can’t tell which is which without looking at the glaze recipe in software or knowing firing temperature though. A glaze that is very dry to the touch is often underfired though, and falls into that first category. If you don’t have a lot of glaze chemistry knowledge and are making pots for yourself and not for sale, using a commercial product that is designed for the purpose is an ideal solution, and will save you a lot of work. If you do want to mix your own glazes, you want to make sure your glaze is fired to maturity and formulated properly and involves a bit more testing. You’ve got some good starting points here, and we always appreciate updates!

If they were just slipcasting and glazes weren’t involved, most clay-based hazards involve inhaled silica, and can be easily remediated with a lot of wet cleanup. A proper respirator is still a must though, because even wet cleanup will stir some things into the air. If there were glazes, possibly lead, involved, we’d need more info. I like Bab’s suggestion about having a cleaning stipulation before move in. edited to add: I’m going to take the liberty of deleting your duplicate post. You probably want all the information in one spot.

Hi and welcome to the forum! We do have a small pinned thread started in the glaze and chemistry section with a few links on working with wild/found/native clays, and you can start there, but I know not everything we have on the forum is in that thread, so I encourage you to do a search from the main page with some of those terms. Others have shared information before. Definitely go through the testing mentioned on Digitalfire listed here, including checking out the article links at the bottom of the page. Characterizing your clay can help a lot with figuring out why it’s doing what it’s doing and will give you hints about its composition. Checking with your local geological survey can also give you an idea of what the clay’s composition might be, which will give you more info on working properties. According to the Potter’s Dictionary of Clay and Glazes by Hamer and Hamer, the cracking pattern of your jug is consistent with bisque dunting. They state that bisque dunting either happens when the firing cools too quickly through quartz inversion, or possibly from being not fired enough to achieve enough strength. Are your jug shards really soft and crumbly? If the speed of the firing is a problem, that could indicate the clay is very high in free silica. If the dunting is an indication of the bisque not being hot enough for strength but you get some pretty extreme bloating only 3 cones hotter, that’s a very narrow firing range. If you want to use this clay, it’s definitely going to have to be amended. Hamer and Hamer suggest fixing dunting due to to free silica by binding the silica up by adding a flux like feldspar. Given that feldspar can also contain a lot of alumina, that might be a place to start. It could also be you need to use this clay as an ingredient in a more balanced clay recipe, or turn it into a more vitreous decorating slip with a bit of flux.

Just for reference, the Archie Bray has their kiln firing costs listed here, and their largest gas kiln, the Bailey that has a stacking volume of 110 cu ft has a stacking space measuring 48” x 60” x 66”. Closer to 5 feet than 6. Montana isn’t super close to Seattle, but it’s not an unreasonable distance.

@yams23 are you thinking you want some form of regular studio membership, a workshop/residency type situation for a small run of pieces, or a kiln-for-hire for a one off? A 6 foot diameter kiln is a tall order, pun not intended but I’m owning it anyways. I can’t even think of industrial settings where a gas kiln would be 6’ wide, even if there are some gas car or conveyor belt kilns that go that deep. There are technical issues in heating a space that large, and the shape of the space plays a big role. The 2 better solutions I can think of are to either find the largest kiln available to you and build your pieces to fit that, perhaps in modules that can be assembled later. Alternately, if the piece doesn’t need to be fired to a particularly hot temperature, you could possibly build a fibre kiln around it and fire the piece in situ.

I definitely recommend working a half day into your schedule to document new work if you can. My photo set up is in between my kiln and where I pack pots for shows. They come out of the kiln, into the kitchen for quick pics, and into bins. The more lead time you can grant yourself the lower the stress levels.

I’d want a slipcasting expert to chime in over me, but calcium is less soluble as temperature increases. Thus kettle scale. So it’s not an unreasonable thought.

Because I do spend an unhealthy amount of time on instagram, I sleuthed around all 3 accounts a bit more, to see if I could figure out exactly what was going on there. All of the accounts you linked to are using assorted speckled clays, not a plain clay with a speckled glaze. Find images and carousels where you can see the fired foot rings of the pots, and you’ll see the evidence. The speckled look comes from either manganese or iron impurities in the clay body, depending on whether they’re firing in an electric or gas kiln respectively. Also, the images you’ve chosen to link all appear to be very matte due to moody lighting, but product listings of the same items on their websites show the work more clearly. All the glazes on all the functional pieces are a satin or gloss. Most notably, the “balance” cup is remarkably more glossy on the artist’s website than in the image posted here. Get a speckled clay body and use the glaze Bill linked, and you should get your desired effect. Edited to add links to the respective artist’s websites: @annemiekebootsceramics: https://www.annemiekebootsceramics.nl/work/tableware @sensitiveboi: https://cargocollective.com/sensitiveboy/index @darc.matter.ceramics https://www.darcmatter.eu/shop/alle-items

As someone who learned patience very much against their will, moaning about it the ENTIRE time: this will only get you so far. At some point someone’s going to make a nasty comment, and the good feelings of cranking stuff out will vanish very abruptly. There is a happy medium between waiting 4 days for leather hard and speed drying in your oven in a matter of hours. It leads to better pots, and all the good feelings about having learned a skill/accomplished what you set out to do on purpose, rather than accepting “happy accidents” all the time.

Hi and welcome to the forum Carol! What do you need advice in regards to?

I keep my kiln shelves (electric) outside in a tin garden shed year round for the last 5, and so far they’re fine. I wouldn’t expect a freeze thaw cycle to affect kiln shelves unless they’re getting wet.

If the powers that be need to see the repair state of the kilns, get them images, and show the side by side comparison to a new kiln. Emphasize that you will not be able to keep them propped up for a lot longer under current usage. Another question to consider is do the sub-par operations or conditions of these kilns contribute in any way to potential liability regarding the volunteers?

I went looking to see if I could find some current information on lead contamination in used pottery kilns and if it was possible to remediate. I couldn’t find a lot of information around lead in hobby pottery in general that was less than 10 years old. (If someone else has better search results than I do, please chime in!) I found one mention in a 20 year old Clayart thread that said you could fire the kiln with a bowl of neph sye in it to absorb lead fumes and you’d be fine, but there was no logic presented, or info on how much lead could be removed by this method. The only reason I mention it at all is because both Roy and Hesselbreth commented in that thread, and neither refuted the statement. But again, I have to stress it was written before 2013, when the FDA decided that no levels of lead are safe. There’s a number of sources though that state lead contamination from a kiln is indeed a possibility, although most references were to folk pottery, or ware produced in countries where lead use still exists. Lead on your pots would be fairly easy to check for, if anyone is reading this and is suddenly concerned about their Craigslist kiln. Many readily available lead tests are designed for things like dishes.

You’re not alone. It’ll teach you patience whether you want it to or not!

@Cajonat if you haven’t yet, make sure you let Plainsman in Edmonton and Ceramics Canada in Calgary know you’re selling these. They’ve both got bulletin boards for used equipment, and stuff goes quickly.

@Traciedyou might get more traction if you create a new post with details about what kind you’d like and an area you want to stay within. Piggybacking on an old post isn’t super effective, and we do go through and clear out old posts from time to time. DM me or any of the other moderators if you need any assistance with starting a new thread. We’re happy to help! To DM me, tap on the profile pic to the left of this post. On my profile page, there is an envelope icon that will bring up the right form.

I suggest weighing how much labour is involved in fixing these, and decide whether or not you want to spend a whole lot of time, additional materials and then money, or just go straight to spending a little money. You’re right, you will have to grind them down and reapply a better kiln wash. Sanding isn’t necessary if you’re applying kiln wash. If you don’t own a grinder, you have to get that, plus any PPE you don’t own yet. It’s a loud, messy job that takes an afternoon, but isn’t the end of the world. It’s what I’d recommend if you hadn’t mentioned the warping which you were compensating for by flipping. If you use a different kiln wash, washes will all eventually flake off. So you won’t be able to flip them anymore without chips getting into the pieces below. If you’ve got the means, just skip to getting new shelves. If you get the thicker corderite ones, they don’t warp, so kiln washing one side is fine. If you spend a little more for lighter hollow core or carbide, they’re more money but are usually a once in a lifetime purchase. Carbide have the bonus of not really holding onto glaze drips.

I have a friend that had to go through medically supervised, in-hospital lead chelation treatment because her employer was using a lead based clear lowfire glaze in an insufficiently ventilated kiln, circa 2001. Negative stars, do not recommend. It was a paint your own pottery place, my friend only worked there for a handful of months, and we had just been through years of school that made it clear lead was not to be used in pottery practice if you enjoy your health. Her employer was “old school” though, and thought the “college kids” were just being “paranoid.” It’s only paranoia if nothing’s out to get you. Given that kilns can last decades with relatively simple repairs and the owner went out of business, it’s reasonable to think that this kiln was sold and might still be out there. Circumstances don’t even have to involve deliberate deception. Lots of folks also have no idea what’s in their glazes and don’t realize that it can be hidden in colourants or frits. I don’t think you need to avoid all manual kilns, but testing them for lead is just sensible good practice, like getting a home or a car inspection. You passing on a kiln that tested positive for lead is a cause for celebration, rather than FOMO. There will always be more used kilns that come along.

The cracks in the bottom are less concerning than the corrosion on the cover on the electrics. As a Cress owner, if anything inside that box is corroded or shot, leave it: they should be paying someone to haul it away, not charging for it. While replacing any individual part is quite straightforward, Cress wiring diagrams are arcane and ridiculous, and they are NOT easy to troubleshoot. Even my kiln tech had trouble with it, and as helpful as Arturo at Cress can be, he can’t do much over the phone.

Another method is to write your post on your desktop and save. To add photos directly from your phone, log into the forum via your phone’s browser and edit your post to add the photo. Most newer phones will give you an option to resize when you select the photo.

I find the best way around this is to either do it the day/ day after they come out of the kiln, or after you unpack after a show. The first is preferable, because you don’t miss the stuff that gets sold. But some photos are better than no photos.