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GavJ

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  1. Yeah that's what I was thinking. As long as the air is only preheating to 600F or 1000F or whatever before getting to the fuel, it should protect the pipe somewhat even in a hotter environment. Although relying on this prevents you from being able to fire the kiln in reduction, yes? Soon as you turn off the air, your chimney is full of slag. I guess you can still do so once per set of pipes... Or maybe the air pipe could be set up to actually be removable during firing? That'd be kind of cool. And fairly dangerous sounding which makes it all the more fun!
  2. No, definitely thanks for your thoughts, Tyler. I'm aware it's super inefficient and that I could make a much better kiln quite easily using modern technology. It's simply a matter of me having more fun / being more motivated by: * learning the various mechanics of the craft available * building contraptions * learning how to purify clay * learning geology * learning historical methods and ending up in awesome situations like gathering my own limestone from a local 19th century quarry site that was apparently 1 block from my house for years without me knowing about it. There are even still foundations of old possible lime kilns or outbuildings in the undergrowth. Just off to the side of this random park. Actually making pottery itself is okay, I guess, but no more so than any of the above. So I'm not motivated to take modern shortcuts to just instantly get to that part of it, because I don't find that part of it terribly special or captivating, personally. If, sometime in the future, I manage to make my own homemade kiln out of homemade local material firebricks, fired with a homemade bellows and charcoal/wood and using glaze from homemade potash and clay, then I'll probably call it a day after making a set of cool mugs or whatever and move on to some other hobby, honestly. Maybe come back to this later when I have a house and land to build legitimate tools on.
  3. Okay. 600F is still way the hell more preheated than 80F air. By "consumable," just how "consumable" are we talking here? Would a 1200 degree pipe melt in one firing? Or do you just mean that it won't last a lifetime? Because a couple of 90 degree iron elbows and straight sections cost only a few dollars. Even if I have to replace it once every one or two firings, it seems cost efficient if it halves my fuel usage, for example. Ideally what I'd want is some graph with "temperature exposed" on the X axis and "number of heating cycles until loss of integrity" on the Y axis for common iron pipe, or something like that. Then I could use the cost of the pipe versus the cost of wood versus that graph to pick a precise maximum efficiency point for me. Then test different lengths of pipe extending further into the chimney until the output temperature is measured at the desired level. Maybe no such thing exists due to it being more complex than that, though. But anyway, yeah it doesn't have to be fully up to temperature of the kiln -- any amount closer = fuel saved. Just want to try and estimate how close I can push it before investing in all the other costs of the kiln.
  4. Thanks everyone. Yes, but are they about to take oxidative damage and/or slump into useless shapes if they go any amount beyond that? Or can they go ahead and get orange or yellow hot first, for a few hundred more degrees? That's the key question. I suppose it might make more sense to ask at a metallurgy forum, though, if nobody knows for sure.
  5. Yeah that's one of the ones I read, I didn't just come up with it off the top of my head. But it doesn't have very good diagrams and the design is all weird because of the ceramic pipes, so I drew my own. Also, I can't afford making it like that. Basically, if iron works, my plan was more along the lines of finding some long short skinny old radiator somebody is throwing out or selling for cheap, and calling it a day... (don't even have to put it upright. Since it is forced air, AND the exhaust isn't super hot to catch things on fire, the chimney doesn't have to be a chimney, it could go low along the ground)
  6. I want to try making a kiln design where the air input (from a blower) circles around a spiral tube inside the chimney, thus using the waste heat to pre-heat the intake and massively increase fuel efficiency (which is going to be charcoal). Simple diagram: Problem is, pipes would be pretty damn hard to make out of ceramic, and probably quite prone to cracking even if I did pull it off. But I don't want to fire porcelain or anything. So I'm wondering if I could do a low fire version of this using steel pipes, and if so, how hot could I fire it without them slumping OR oxidizing into dust? In general, how long / up to what temperature do steel components like grills work in you guys' kilns? Or cast iron or whatever other metal I can buy tubes in, if steel isn't the best option. Also, any other issues to look out for? Like a need for expansion joints where the pipes meet the walls, or whatever? Or if I can get away with it not breaking, would I still have to support the spiral like every 3 inches or something to stop it from slumping into a useless pile?
  7. You jest about the grout, but that is actually extremely easy. Grout is basically just sand and cement. So... semi-homemade is buying a bag of cement and a bag of sand and mixing them (ratio depends on gap size) although that isn't actually all that homemade, since it's not that different from buying grout. Fully homemade is medium-easy and would consist of digging up some sand from a beach or whatever, and gathering some limestone, "firing" the limestone, slaking it, then mixing the sand as before. Which is much less of a harrowing prospect for somebody who already has a kiln (limestone won't hurt it - tons of people already use limestone for normal ceramics anyway, as "whiting")
  8. $80 spoon, sounds legit. But yeah, the spoons look absolutely terrible to me, like they'd shatter from a gentle breeze, as well as looking slapped together and sort of cheap. I DO like the cheeseboards though. (At 1/4 the price, but still).The canvas works just fine for a large surface. As a non-potter just dabbling, I haven't had anything drilled into me about canvas, nor do I have experience seeing it all the time and getting rid of it, so it strikes me as just kind of cool looking for ceramic to look like cloth. But not too in your face ridiculous.
  9. It would be stronger if you made adobe instead of just raw clay. I don't actually know if it would be workable enough, though. Make maybe something along the lines of 70% clay, 15% sand, 15% (quite finely minced) fiber? This is not what they use for adobe, but that's because they make big crude rectangular bricks and walls, not little pinch pots, so I'm guesstimating it closer to the raw clay. You could then use very small amount of heat to burn off surface straw that would mess up your finish, then paint. And it should be quite a bit stronger than just greenware. IF you can actually still make what you want, which you might not be able to. If it is workable enough, though, I'd try to increase the proportions of sand and/or fiber until it just barely isn't, and work near there. Also, firing clay in the coals of a barbecue is one of the few things I actually have real experience with and have done some decent amount of reading on (well, pits more so): low fire earthenware clays will generally hold up BETTER than fire clays or porcelain, due to usually higher thermal shock resistance. So your backyard clay might work in the barbecue stressfully quick firing while fancy white store bought clay might not, somewhat counterintuitively. Tempering the clay will also help. Even the same recipe above would help quite a bit to prevent damage from rapid, short firing: the sand is just grog, and the fiber will burn off and allow porosity and quicker heat penetration and thus more even heating and less breakage. When I have done this, it's still brittle (as I have been led to understand in another thread, probably mostly because I didn't hold it at heat long enough and/or heat slowly enough), but it's WAY better than greenware still. Probably takes 3-4 times as much force to break the same piece "fired" this way than its greenware equivalent (without tempering)
  10. Oh, I wish I had seen the last post here earlier, but yes went ahead and checked out some books and discovered the same thing stated immediately above: ash glazes appear to be almost exclusively cone 9-10, which I cannot achieve. So basically, you're saying I have to just use pure potash as my "raw" ingredient... wonderful. So instead of 0.5% of wood I get to use, like, 0.005% of wood. *sigh* But that's okay. So just to double check, the process would be: 1) Burn some stuff (using charts to try and guess best local material for high sodium or potassium concentrations) 2) soak the ashes for a long time, mixing occasionally, and retain the solution. Maybe a couple of times. 3) evaporate the water off, getting crystals (carbonate) <- edit: that would probably be dumb, when they're just going right back into water again. Could just use the solution FOR the slaking. Although would have to check to make sure potassium carbonate doesn't itself react with quicklime itself in an undesired way if so, since it would be exposed to unslaked lime if done this way. 4) Mix the crystals with a limiting reagent amount of clear slaked lime in solution. 5) Filter the resulting precipitate (Ca carbonate and a small amount of excess Na/K carbonates) 6) Evaporate off water again, then use the crystals (K2O and/or NA2O depending on plant) in glaze in large proportions as flux, mixed with as much local clay as I'm able to reach a melting temp for, for its silica and alumina base Yes?
  11. After extensive searching, I am unable to find much or anything in the way of people using wood type finishes on unglazed fired pottery, in place of refiring with glazes. For example(s), terracotta or possibly even raku + * polyurethane coats * drying oils like linseed * beeswax * for a different coloration and look, something like a drying oil combined with limewash etc. Obviously none of that is appropriate for, say, oven use, but for tableware, why not? Coming from more of a woodworking background, these things seem straightforward and intuitive, but the lack of any actual examples of them I can find gives me pause.
  12. Ah, nice. So that link suggests it may have as much to do with my cage of fuel causing reduction then as it does temperature and time. I may just have to suck it up and find some way to build an actual kiln then to fix it, where the wares will have full airflow. Or perhaps really upping my game on the strength and directness of my airflow line (which gives two things to try immediately!)
  13. So just unwashed ash then, yes? Or would already leached potash be better? Or even calcined pearlash? I have quite a lot of all of this on hand already as I'm also working on glass making. I.e., is the lye helpful for the glaze, or just a contaminant? Since it sounds basically like just the recipe for normal soda glass with clay instead of sand. Also, thinking from that point of view, would 5-10% calcium carbonate help it be more waterproof at the end, similar to soda glass? I do have access to both local chalk and limestone. (Yes I will look for a book too =)
  14. I'm not sure what people are referring to here by "bisque firing" since AFAIK the term, bisque firing is what I'm already doing (firing at sintering temperatures without glazing)? Sorry I'm very new to this. If by just higher temperatures, I can't do that yet, because my project is to only use local materials that I have made or at least have made before (grill itself doesn't count, because it is just standing in for a dirt pit that I don't have a yard to make, and it confers no other advantages. Air stream will be replaced by an actual homemade bellows by the time I do my final pieces eventually). Some day I will have gathered or sourced enough materials and friend's land to build a larger kiln that can hold more heat and will certainly be using it at such in the event that I just need higher temperatures. Anyway, until I can upgrade, there might just not be anything I can try other than a longer soak. I just didn't know if it might have been TOO much heat for earthenware. So thanks all! (By the way, note that I am using charcoal, not wood, and using a large amount of forced air, which would burn hugely hotter than an unventilated wood trench.)
  15. It may very well be cone 012, I don't have any official means of measuring on hand. I was just going off of pyrometric charts online that equate different levels of glow/black-body radiation with cones. Note that these are not just sitting on top of the barbecue or even just on top of the coals, though. The wares were completely surrounded in all 3 dimensions with brightly burning lump charcoal, and I was directing a steady stream of air at them from a blower made for small pipe organs. They go bright orange-hot all over, somewhere between orange and yellow, which is anywhere from 04 to 1 depending on what chart you look at, so I hedged at 02. Could be very wrong. The organic matter still in the interior makes a lot of sense with such a short firing, though. I can definitely try upping it to an hour or an hour and a half without going through too much charcoal. I'll see if that more fully burns off the organics, and might help on the strength too. I can't for various reasons use a proper kiln just yet, but may be able to soon (lack of a location to legally fire one on for now. Grill is incognito. Also, certain self-imposed artistic constraints) Also, use of a grill is just coincidental, I guess. It was just a natural choice as the only place I can make hot fires at the moment without risking drawing too much attention, that's all. I also used a similar setup back in college to cast some brass, which melts at about 1700 and casts easily around maybe 2000, so I remembered that and figured it should be enough for earthenware, too.
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