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  1. Interestingly, in the permaculture community there appear to be people creating wood-fired cob forges and rocket-stove forges, which may be a starting point for a design that's not tied to firebricks. Charcoal is also another option if need be for more consistent results, but that's another off-site input. If I do end up exploring a partly cob-based kiln I will definitely report back any results (or failures). It seems like experimentation may be a better choice if no books show up, so long as there is no cost involved other than basic materials.
  2. I've heard about converting electrics (whether to gas or wood), but that's another investment to make (though I understand picking up used can be the chepeast way to get good firebrick), not to mention it's suddenly bringing a lot of needless technology and ugliness into what is essentially a primitive endeavor... I would prefer to do something more traditional... part of the desire for wood-fire is because I don't want a lot of external inputs to make the process work. Ideally I would use some (perhaps double-walled) cob-oven type design and not bring any off-site materials (no firebricks)... My suspicion is that 3/4ths of the design choices I see being made in many of these kilns comes from the desire to fire at high temperatures, to fire quickly, or to achieve reduction or ash effects. The raku wood-fired kiln designs I am finding appear to at least be build for the lower temperature, though they seem to usually be designed to achieve that temperature rather quickly. Seems strange to me that if everywhere other than asia rarely fired much above 1750F and rarely used anything like firebricks, and everywhere including asia was without electricity or propane, all the way up to a few hundred years ago, then there should be many established repeatable designs for a reusable kiln for small loads. Perhaps an old out of print book. I have the Cardew book and that's certainly a starting point but he's building large and firing hot... I can extrapolate, certianly, but I'd think there'd be some historical or revivalist book that would be more fitting.
  3. I'm exploring making a wood-fired kiln, but all of the resources I am finding are for firing at much higher temperatures than I need and also for generating ash effects. Here are my needs: - Firing to somewhere between 08-04. Traditional terracotta. - A reduction environment is not needed (and probably not wanted) -- this is for figurative sculpture. - There will be no glazes, this is just bisque firing. - Firing box would have to be able to contain an object of maximum dimensions of 12x18x36, oriented in any direction. - It would be ideal if I could keep the design and fire box as small as possible as it would be preferable in every way to fire small amounts more frequently. Basically I'd want to recreate the firing properties/technology of a 16th-17th century terracotta kiln, but plan size scaled down to the minimum possible size for a small cache of works. Any recommendations on a book that would cover the principles I needed to know (or have ready-to-go designs) for these needs?
  4. I am a figure sculptor (haneebirch.org/artwork -- out of date, but gives a basic idea), and I've worked over the years in a variety of materials, both clay and non-clay. I've been steadily working towards more detailed work in the past couple years (none of which is on my website yet), and while I love the feel of a traditional red earthenware body, I am sometimes feeling like I am at it's limits (or rather, my limits!). I'm trying to explore which clay bodies will work best for both the early stages where supple gesture and the ability to make quick, dramatic changes to the pose, is the needed feature and the latter stages where things like modeling a tiny 1/3rd scale nostril or eyelid, or lightly smoothing in a controlled manner that doesn't merge forms too easily... Anyhow, introductions aside. I got a couple boxes of WED clay (Laguna EM-217) about a year ago. At first the stuff seemed almost like a bad batch it was so intensely sticky (and I usually like sticky products, as I used to work in wax). I still am not sure if I got a bad batch, but I have learned to work with it. It seems exceptionally good for finely controlled form at the later stages of sculpting, but at the early stages it can be a real sticky mess compared to a good terracotta body or the raku/sculpture clays I've used in the past. I am trying to understand what exactly is different about the clay. All the public information on it always emphasizes the slow-drying qualities (and the fact that it's not ideal for firing, but can be fired nonetheless) -- I don't particularly care for it's slow drying nature as I work quickly, but, what I notice and appreciate more than anything when using it is that it has a certain density that resists pressure. For example in my standard laguna terracotta body (and most similar clays I've used from other manufacturers), there seems to be a "spongy" quality. Pushing in one place deforms other places and it is so soft, even when at the equivalent moisture level, that crisply modeled forms easily round over if touched indelicately. On the other hand, WED holds detail and you can easily run wet cloth over a sharp form and only take a hair's breadth down off the sharpness. It's density is more similar to raku clays I have used (which I believe usually are a stoneware base), but it's plasticity resembles most some 'wild' clays I've dug which I believe were extremely carbonaceous -- almost completely unworkably plastic unless in a rather more-dry state than I would habitually use a clay at. I'd like to either locate a similar clay to WED, that doesn't have substances added to slow drying, and that is perhaps a tad less sticky or "fat" as they say, and that ideally fires to as-strong a product as a terracotta body does at cone 06-04. I will mostly be using it for casted works, but it's nice if I can use the same body for firing when need be. Any thoughts on what the constituents might be, or at least what types of clay might be similar (very-dense/extremely-plastic)? I am guessing (based on some research and my own very limited experience) that it is a stoneware base (dense) with a lot of ball clay (highly plastic). It also has a bit of a chemically/bleach smell when new which disturbs me -- perhaps it is whatever "retarder" is added to slow drying. It seems to also have a far, far narrower range of workable moisture levels than my usual red terracotta, if that's another clue. (In the UK a similar product appears to be sold as "Potclays Modelling Clay" -- https://www.potclays.co.uk/studio/products/5242/modelling-clay-157-1150-1100-1280c )
  5. @Marcia Selsor -- Thanks for the book reference. Books are usually how I learn these things. Correct, the Bacchus I believe is a unique original. Most the works by the bigger names in that period are, but books always mention lesser works that were mass produced and a few are specifically credited as cast. @Sputty -- Wow, thanks for that video. Extremely helpful. I am curious since you seem to have some historical knowledge on this: many of my books seem to indicate press molds were used rather than slip cast molds. Slip cast seems like it would be far easier (since you can cast enclosed forms without having to later joint them). Is there any reason that a press mold would be avantageous (I can only think of disadvantages) or is the slip technique just historically more recent? I am still debating just how worth-it doing terracotta casts would be -- obviously it would be a labor of love; I'm not sure if the market will really care to make as much of a distinction as I do between some fake-bronze resin cast from silicone and a ceramic piece assembled and hand-finished from piece molds. Anyhow, your video is an invaluable aid as far as some directions on how to go about it, if I do decide to for some of the simpler figures. I do believe silicone could work for press-molding if done just right and it would allow a two or three peice mold in most cases -- but obviously it wont work for slip casting. I will have to experiment to see which method, all said and done, is the lowest labor for equal results. The purist in me would prefer a plaster mold, if I can acquire the requisite skill. Thanks again for the video link. @Chilly -- I only know of one places that I believe might do slip cast lawn-figures and the like, but it is about three hours away. I will ask to take a peek the next time I am near. Overall, it seems a good first step would be to chose one of my simpler figures and mold a version in which most of the smaller, more complicated undercuts are filled in to reduce the total number of pieces needed to piece mold, then cast, and rework the undercuts and complex areas. As my molding capability increased I could mold more pieces accurately and re-work less. Obviously this is a very hard-won additional skill and it would be better to take it slow and steady in terms of increasing complexity if I'm going to rely on it as a primary tool of production.
  6. I'm a figure sculptor who has worked in the past in direct-terracotta (http://haneebirch.org/artwork). I have a new body of work I am in the process of putting together, and for practical/economic reasons I am going down the road of mold-making and casting instead of direct work. Unfortunately, this usually means moving from terracotta to plaster (or worse, plastics and the like). I don't mind plaster but it's hard to touch up and doesn't have much value to most people -- ends up needing a patina, etc. So... What I'd like to do is find out how to cast terracotta figures as was commonly done in the 17th and 18th century. All my catalogues of figure work from that time period always refer to cast-terracotta being fairly common. But, nowhere in modern method books have I ever run across anyone who seems to see such an undertaking as even conceivable. Take this figure by Clodion for example, in the Met's collection: http://www.metmuseum.org/art/collection/search/200559 So, I do have some experience with mold making, but I've never been the greatest mold making. I seem to be competent at waste molding (except I've never gotten a great release agent recipe that really works consistently, seems like sometimes I get lucky and have perfect release, other times something in my application process must fail), and am capable though not exactly confident with my brushed on silicone molds. In my limited mold knowledge I am guessing this peice by Clodion was press-molded, in a multi-part piece mold. Still, it's hard to comprehend how exactly that would have been done, with the bird wings and many undercuts. For myself, my figures are fairly unadorned but the poses are still complex. I can imagine that I could ignore many of the undercuts, cast a rough form, and then I could easily clean it up, add depth, put the undercuts back in. But still the piece mold for a basic figure of non-trivial pose (say, http://haneebirch.org/artwork/chair-no-1 seems beyond my comprehension). Even chopping the figure into separate parts and re-attaching doesn't simplify it all that much, and I'm unclear on how exactly that would be done anyway. So is there anyone who would know of any book or person that could describe all the technique needed to press-mold or slip mold that Clodion figure or the figure I referenced of my own? Is there some alternative technique that I am not aware of that makes this all a simpler proposition than I thought? I have tried press-molding in a silicon mold, and, to some degree, it worked, but how to cleanly joint the pieces and how to control for moderately even drying seemed unclear (though perhaps with enough experimentation). Anyhow, before trying to blaze my own path with modern materials, I'd really ideally like to find a source who can make entirely clear how exactly this was commonly done in the 18th century. Thanks in advance for any information.
  7. hanee

    Working-Strength And Grog.

    Highbridge, that's really fascinating. If we're both understanding this particular diagram correctly that would mean that the reputable sources I'm reading are only speaking of grogs impact on shrinkage/drying issues because it perhaps has no significant impact on green strength in the concentrations we usually use it. Do you know when they say % are they usually referring to by-volume-% or by-weight-%? I recently got a copy of Daniel Rhodes' Clay and Glazes for the Potter, based on recommendations on this forum and the only references to grog are in terms of shrinkage/drying. Seems counter to everything I learned in my figure modeling classes way back when, but I expect potters know more than sculptors on this one. JBaymore, the kind of strength I'm looking to optimize for primarily is that of an outstretched limb. Secondary to that is compressive strength (say, all the weight of a figure on one leg). Both in the early-green state (i.e. working consistency). Empircal testing is great, but it's nice to have some knowledge to give a bit focus to otherwise random permutations, if such knowledge can be had.
  8. I'm interested in learning more about how grog affects working strength. In most articles I can read online about grog the primary effect seems to be to aid in even-drying. Most articles talking about strength and grog also are seem to be primarily discussing it's effect on the fired product. For example, the article on digital fire about grog doesn't even mention it's effects on working strength. On the other hand, I've always experiences that a grogged clay will be stronger in-working than an ungrogged clay of the same body. I've heard this reaffirmed in manufacturers descriptions and from othose I've known in the past, also. But I'm not finding any thorough source explaining how grog amount and coarseness relates to working strength (in terms of supporting an outstretched arm, for example). I'd like to determine an ideal percentage and coarse-fine ratio to use when optimizing an earthenware body for working-strength versus any other feature (fired strength, dry-ability, etc). Anyone care to explain this or refer me to a better source than the one's I'm finding?
  9. alabama - The local clay I've got is definitely clay, not dirt. Extremely plastic and very good wet and green strength. Still haven't fired a sample -- I will do that in the next kiln load.
  10. Thanks to everyone for all the recommendations! (though it appears all the ones I'm most interested in are both out of print and surprisingly pricier than I expected for used, but several seem worth the premium price) And alabama's advice of individual trial, error and analysis is spot on, especially as my needs will probably not run in the needs of most potters, being a figure sculptor.
  11. Benzine, Haven't really had much in the way of shrinkage problems, it's all for build strength. I haven't the skill to do things like these without grog, though I know Bruno Luccheshi manages to: I'm sure it could work without grog if I tried hard enough, but it's quite difficult for me to manage to work without an armature to begin with, and adding the extra challenge would make the working process all about how to coax the clay into submission instead of letting that fall into the background and putting all my energy into composing and modeling the figure. Also, sculptors work additively as much as possible, so having to have your clay firm up and cut it back is really going to take away from any suppleness of modeling... In something like that child figure above (pond-no1) the head is massive, and even though hollow, it's on a very skinny neck and wants to fall forward. I propped it while working but it's never ideal to do that because it gets in the way of modeling features or noticing asymmetries. If it was not well-grogged clay I would have to prop quite a bit more, might sag and lose the back bend, whole thing might compress as I worked, etc... I like the feel of modeling with grog, too, nice materiality and all, it's just the small details or final surface stuff where it ends up being a big pain sometimes. And I don't like the multi-colored bumpy speckles left behind after firing on more refined work... (Also it seems for good build strength you really need a substantial amount of grog -- the raku clay I used for that figure leaning on a counter was far stronger than the sheffield MGB I used for that child figure; even though the MGB has just the right kind of very-coarse grog that's supposed to be optimal for strength it must have far less total grog than raku clays usually have).
  12. I'm planning on formulating some clay from a few native deposits and/or mixing from purchased dry materials if that doesn't work out for some reason and am looking for a good book that I might be able to turn to for little questions/tips along the way. I don't really need any coverage on glaze issues, just clay issues — something for people who like to do things themselves and want an understanding of the variables at play. Especially good would be something that had a historical/low-tech orientation. Wouldn't mind finding a book on kiln constructions (especially DIY kilns and historic woodfire kilns) too but that's a bit more of a daydreamy future thing...
  13. Chris, I'm working low-fire so I'm wondering if I should expect a higher success rate with a second layer in either case. Thanks for the explanation of terra sig, I know about it, but have never used it as I've never used a glaze process. The way I'm understanding your explanation of the sig is that it's effectively cracked already as its individual particles are filling in between the other clay particles and there are gaps in between, so you're not dealing with an eggshell thin layer that might crack but more of a spatter in which the individual dots moving apart, even at different rates, isn't going to cause any aesthetic issue. --- With the thin layers thing, still a bit confused. I'm not adding wet to dry but clay of the same moisture content to the same moisture content. Benzine, I do smooth the surface in some places and the new clay body I'm using which contains large grog and no small grog smooths quite nicely, when I want it to. The old clay was not as good at that but not terrible either. It's not smoothness that's the goal so much as modeling. It's within the modeling process that the grog gets in the way (though I can work with it fine, it's just it would be a dream to not have to battle with large particles of grog when making a 1/8th inch eyelid). Not looking for a way to get things smoother, per say, but looking for a way to model finer detail with a bit more plasticity/workability while still having the strength I need at the earlier building stage for support of outstretched limbs and the like.
  14. Thanks! I will go ahead and risk it on my next figure, as it would be nice to have the possibility of relying on a high grog formula for strength but still being able to have a more refined surface if needed. I do have a question for my understanding: when people use terra sig aren't they effectively doing the same thing as putting a high-shrinkage clay on top of a low-shrinkage clay? Is it the *thinness* of the second layer what allows it to work? If so, why would a thin layer be any less subject to cracking than a thick layer? I'm not quite understanding why thick vs thin would matter.
  15. Crusty, unfortunately I'm not making joins -- I'm a figure sculptor and model with many little bits of clay constantly being added. If I find that it wont accomodate my working methods, I will change the body or give it away if it's unchangeable. Not going to sacrifice the quality of my work for a misbehaving clay. oldlady, I will try contacting them, but I'm betting this is a difference-of-application issue. Perhaps it would make a great throwing clay, but for sculpture, it's quite a pain. Tolerable for some depending on their working methods perhaps. Neil, I've mostly used terracottas in the past, and also a decent amount of raku clays. I wouldn't call them particularly sticky but this clay is out of all my norms I'm used to. I don't really have experience with anything outside of terracottas, raku clays and a few general purpose school-clays back in college (stonewares mostly I believe). As for moisture level, I don't think that's the factor here. I work with a wide, wide variety of moisture levels and reuse clay. I use it just as often out of a rubbermade of sprayed down scraps as I do out of the bag, I'm used to how most clays work in this range of conditions -- this one is out of all my norms and resists adhesionin in cases where every other clay body I've used, even not particularly plastic ones, would adhere fine. As I said, the interesting thing is that the theoretically less-plastic *grogged* version adheres far better than *ungrogged*. Is there a simple explanation for that (perhaps the clay resists moisture and the grog helps to break up that resistance and carry moisture inward, increasing the bond)? On reflection, I'm not that experienced with ungrogged clays so it may be some of the things I'm describing are a product of the lack of grog in the smooth body, and perhaps even in the coarse body, since this particular formulation uses all coarse and no fine grog which is different than most commmercial sculpture preparations I've used which contain a mix of both. The counterpoint to this theory, though, is that, as I said, I have a native clay (also an earthenware most likely) that I have dug up that is almost as sticky as vaseline with no grog. My instinct tells me that at least part of the problem is that this is just way too fresh of a mix, it just feels very sterile and bodiless compared to other clays I've used. It's hard to believe that their base is so radically different from all the other terracotta-sculpture bodies I've used. Perhaps tossing a bit of organic matter in and letting it rot a bit would improve things...

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