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Ryan M Miller

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Everything posted by Ryan M Miller

  1. A lot of entry level gardening books on soil health define clay particles solely by size (2 μm and smaller). This is generally fine for defining soil texture, but not useful for defining a pottery clay body since not all particles in this size range have the properties of clay minerals. In addition to regular illite, bentonites, montmorillonites, kaolin, and other aluminum silicates, there may be other particles in this size range that do not add clay plasticity or expansiveness; for example, if I have a bag of pure quartz particles (silicon dioxide) that are 2 micrometers and smaller and then I attempt to add distilled water to it to make a clay body, would the resulting paste still have any plasticity or wet strength to it that would make it useable as a clay body? I feel that I would be lucky if I at least get some kind of melted glass that leaves a mess in a kiln from such a "clay" body. What if I have a bag of dried peat or muck particles that are 2 micrometers or smaller? The resulting paste when water is added would not be suitable for firing in a kiln even if it does have suitable plasticity or wet strength since it would just burn away if it were fired in an oxidizing environment. Similarly, if I attempt to make a clay body of limestone (mostly calcium carbonate) that has been ground down to 2 micrometers or smaller, the resulting paste would just reduce in the kiln, turn into caustic quick lime, and gradually crumble apart as the fired object is explosed to atmospheric moisture.
  2. I want to test claims that slip-casting developed prior to the 18th century in Europe by confirming what deflocculants could have been used. I recently did some further reading on sodium silicate and its possible that there might actually be naturally occurring minerals that contain sodium silicate. Unfortunately, the only article I could find was a paywalled article from science direct. A Google search for naturally occurring sodium silicate yielded the following auto-generated quote from the paywalled article as the top result: "Sodium silicate minerals can form by evaporation of highly alkaline interstitial brines in near-surface horizons. The most common sodium silicates are magadiite, kenyaite and kanemite." If any of these three minerals exist in Peru or the Yingdezhen region of China, they might have been used in slip casting after multiple trial and error discoveries.
  3. I started this discussion on whether or not paper pulp is a good temper for slip-casting. After further reading and YouTube videos, I have learned the importance of using deflocculants in slip-casting. The most common deflocculants I find in modern slip-casting recipes are sodium carbonate, sodium silicate, and Darvan®. With the possible exception of sodium carbonate, all of these deflocculants seem to require an knowledge of modern chemistry or at least medieval alchemy to synthesize. I have read that slip casting may have developed independently in China in the construction of early Jingdezhen pottery and in the construction of clay pan flutes in the first century of Peru (here) so alternative deflocculants must have been in use in these two independent locations in order to form a thick enough casting shell. Two other potters I've consulted suggested using wood ash or tannic acid as deflocculants sincetjese materials are easy to obtain and still have deflocculating properties. I will have to test these two previously mentioned substances first to confirm these recommendations. Before I do any tests with wood ash or tannic acid, I want to comfirm if any potters in this forum have ever used alternative deflocculants in slip-casting.
  4. I have asked a few other potters about alternative deflocculant materials. I will begin a new thread here shortly. Any admins may close the thread if they think it's necessary.
  5. I have been reading more on slipcasting and it looks like I forgot to factor into account what material will be used as a deflocculant. I was unaware of the importance of adding sodium silicate, Darvan®, or washing soda to the slip. Now I'm wondering how these deflocculants could chemically react with organic temper materials, especially since wasing soda looks like the most readily available defloculant for me.
  6. It sounds like I'll definitely have to do a test fire first. I am aware of prehistoric potsherds that show plant fiber was used as a temper material in the piedmont of the United states. These pots were often fired in a pit fire so they would be subject to thermal shock at least during the initial firing. At least some of these potsherds are identified as belonging to cooking vessels Here is a link to a relevant journal article. Unfortunately, these prehistoric pots would only have been hand built either with the coil and scrape method or the paddle and anvil method so the example pot sherds do not answer whether or not a fiber based temper will remain suspended in a slip during a slip cast or if the temper material will settle too fast.
  7. By pot intended for cooking, I mean one that will be used primarily on either a gas burner or bed of coals. It should function something like a Dutch oven if it were made of earthenware clay instead of cast iron. The pot must be able to withstand the thermal shock of heating and cooling during cooking so that it doesn't shatter easily even when heated slowly.
  8. I am interested in building a plaster mold for an earthenware slipcast pot intended for cooking so I would like to know what temper materials would be suitable for a slip that won't settle to the bottom of a casting during the formation of the skin. Obviously, sand and grog don't qualify since they would settle in less than five minutes, but I am curious about the possibility of using paper pulp, dung, or other plant fibers as the temper material for the slip since organic fibers tend to suspend in water more readily than sand or grog. If any more experienced potters have successfully slipcasted with either stoneware or earthenware paper clay, please let me know. If paper clay is a viable option for slipcasting, then it means that I can make a stackable set of matching cooking pots more easily and faster than if I were to hand-build the pots or throw them on a wheel.
  9. Since I couldn't find a general new user introductions thread, I guess I'll post here. In the meantime, I will be searching the forum for beginner ceramics topics.
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