I've been trying my hand at a kind of pottery dorodango(very smooth mud ball, basically) for a bit now, without any dedicated pottery tools since I don't have any and just picked this up out of nowhere.I got local clay from dirt using buckets & cloth, then molded it with my hands, burnished with a metal spoon and fired it on the coals of a charcoal grill, surrounded by aluminum foil.I've tried several times to make a full ball, and though the molding, drying and burnishing go off mostly without issue, when it comes to firing all but my most primitive piece have broken apart. I've decided to try out a disk, figuring that the reduced internal volume could help trap less moisture and reduce odds of explosion, but since this is a decently labor intensive process, I'd like to ask you guys for any tips you have to help prevent cracking. Is there some method that I can use to make it less likely to explode? Could my clay + grog use some additive? Maybe I should poke some holes into it (though it would ruin the aesthetics)? Maybe sundrying it for a week? Any tips, really.
>>3009291It’s likely exploding due to gasses on the inside. Most of the time it’s because the clay is not dry enough and the heat boils the water and the steam causes it to explode. Something like that could take quite a long time to dry. I wouldn’t be surprised if the water has a harder time getting out due to the surface finish but idk if that would actually happen. The way we tell if clay is still wet at the studio if to put it to our cheeks to see if it is cool to the touch. Leaving it somewhere dry or maybe putting it in a sealed container with a lot of silica gel packets would help. Putting it in an oven set right below waters boiling point could also work.Probably the best way to save your pieces though would be to not fire them. I don’t know what the grill would do frankly. I’ve heard some potters fire their burnished pieces at low cones like 018, but that’s still over a thousand degrees Fahrenheit. Maybe grill coals get that hot idk. Does your firing process noticeably change the claybody you have?
>>3009291Get a pottery lathe.
>>3009291Pottery tools are basically paperclips and popsicle sticks. To fire clay it must be totally and absolutely dry and you said nothing about racking and letting it dry so I imagine that's your issue. Also all dirt is not created equal, I don't believe good clay mud exists everywhere, just like mor all beaches have sand and not all sand is nice.
>>3009298>I wouldn’t be surprised if the water has a harder time getting out due to the surface finishI see. This does make sense, if I consider that the unfurnished, superficially cracked ball managed to survive firing(though it is also smaller).That could be an issue, as the whole idea was to make a very smooth object. Do you think there'd be a way to still achieve a smooth finish while keeping it porous enough for moisture to escape?>Leaving it somewhere dry or maybe putting it in a sealed container with a lot of silica gel packets would help. Putting it in an oven set right below waters boiling point could also work.Very interesting. So far I'd been letting them air dry, then sun dry. This could be very useful.>but that’s still over a thousand degrees Fahrenheit. Does your firing process noticeably change the claybody you have?Well, all the pieces so far, despite breaking, *have* become waterproof, surviving being submerged in water for >24h. They also make a neat little *dink* sound when I knock 2 pieces together, so I assume it managed to become ceramic, but maybe this is just partial? I do want to fire them to make them "permanent", if you get what I mean, but to be fair the unfired, burnished pieces already look and feel pretty neat.>>3009299Would that help with the firing? I also don't have much space in my home for anything big.>>3009301So tools are kind of optional? About letting it dry, I've been letting the pieces air dry after molding for about 8 hours, then burnishing them while they're partially soft, and letting them further dry in air/sun for 24hrs. Is that not enough for such dense pieces?How can I tell if my clay is good? I separated the organics and the sand using a bucket and cloth, so not exactly the purest process, but it felt pretty smooth in my hands, and kept the shape pretty well when molded.
>>3009311You should look up just generic stuff about how potters burnish their pots, since it might be helpful for you. Some people dry the pieces 100% and then burnish them. There are a couple of methods this way. Some people will slightly re-wet the surface and then smooth with stuff, like your spoon, or some use plastic bags. Some people also oil the clay and rub it in. You should also read about terra sigilata. It is basically superfine clay particles which are used to burnish, and they get a nice surface a lot easier. It’s what the Romans and Greeks did. Although the other anon could be correct that your clay is bad, I think that the fact that it fires to some extent means it’s good enough for your purposes. My advice would be to make some balls that you don’t burnish, and test ways of drying them and fire them to see if there is an improvement.
>>3009400>Some people will slightly re-wet the surface and then smooth with stuffThis seems like a very interesting idea. Maybe allowing superficial cracks to form early on would permit the moisture from the core of the piece to escape, which I could *then* follow up with wetting the surface and burnishing. I'm not too confident I wouldn't be just reintroducing moisture to the core like this, though.>terra sigilataThis is a very interesting concept. I have previously managed to crush clay into an extremely fine powder (that I have, on one occasion, nearly got a lungful of. Unpleasant.) via breaking and then sifting clay through 2 layers of cloth. It was extremely soft to the touch, and could go airborne with very little effort. Would this be terra sigilata, or is the method of making it finer?>make some balls that you don’t burnish, and test ways of drying them and fire them to see if there is an improvementI'll do this. It's almost stupid that I didn't try going back to the one example that actually (kind of) worked.
>>3009494realized I said 'very interesting x/y' twice in a row. Vocabulary of a retarded ant.
>>3009494The terra sigilata isnt crushed clay. Well I guess you could make some from crushing but it’s made much much easilier. Since clay particles are charged and will attract and stick together well due each other they will clump up and sink out of suspension. The sigilata process is letting the clay settle for a while after being mixed into water, and siphoning off the middle layer of the mixture, since the top is too watery and the bottom layer is too thick and has the largest particles. The middle layer has the very fine particles that haven’t sunk to the bottom yet. I assume you can do it with just water but some additives like sodium silicate (water glass) or sodium carbonate will prevent the particles from sticking as much and the slower process means you get more fine particles still floating in the middle layer but it takes a lot longer to settle. Maybe your crushing followed by the water settling filtration method would make it even finer.
>>3009499I see. This has been an enlightening conversation. Seeing as the current disk has little that can be done to it without recycling, I'll just fire it as I have done previously, but all further experimentation will follow your advice. I might post the results here once I fire the disk after it dries out for a week or so.Thanks a lot for the help.
>>3009503before you try and invent a process to siphon off only the middle portion... just siphon out the top first
>>3009532Gotcha. I'll see what I can do.
>>3009291Another thing you could try is putting the ball into a vacuum chamber for a few days to draw the moisture out, then burnishing it and drying it in the oven previous to firing. If you need water to burnish it add as little as you can and do the vacuum and oven cycle again afterwards, what you want is to get all the water content out of the center which being so far from the surface might take a long timeYou could also fire a smaller (dried) ball and keep layering more clay on top until you reach the desired thickness, or forego the clay core entirely and start out with a metal or glass ball or something that can take the heat and make just the outside clay instead
