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Sequoia Pottery

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  1. I've seen those kinds of figures with most "smectites", and it's still hard to imagine. You'd think those tiny particles would help fill in voids in a fired clay body. About filling in voids, THIS is interesting, https://www.sciencedirect.com/science/article/pii/S1877705813008060
  2. I looked up my notes about using 20% (actually), sepiolite in a cone 05 clay body. I got 20 percent shrinkage after firing and had close to 0 absorption with 10% frit 3124 (boro/calcium/alkali. About gelling, you said, " Same is true for the calcium bentonite (saponite) I am looking at at the moment. " I have a one pound sample of the following saponite, but it has WAY more calcium than advertised, so I didn't really experiment with it very much. All of these materials are of very small particle size. Hey, please post what happens with your 15-35-30-20 experiment. TYPICAL CHEMICAL PROPERTIES %_ TYPICAL PHYSICAL PROPERTIES PACKAGING IMVITE 1016 is a gelling clay obtained from saponite clay, a magnesium bentonite. 1 (Fresh Water) Yield, (bbls/ton) ............................................................. 95 Viscosity, Fann @ 6% solids 600 RPM, ......... 30 min. overnight Plastic Viscosity, (cps) .................................................. 3-4 Yield Point, (lbs./100 ft) ............................................... 29 Water Loss, (cc) ........................................................... 19 For test procedure in API 13A and 13B.. Fann Viscometer dial reading at 600 RPM. Silicon (SiO ) .................................................................. 44.6 Aluminum (Al O ) ............................................................ 7.8 Magnesium (MgO) .......................................................... 22.8 Iron (Fe O ) ..................................................................... 2.5 Calcium (CaO) ................................................................ 4.5 Potassium (K O) ............................................................. 1.3 Sodium (Na O) ............................................................... 2.5 L.O.I. (1000 C) ............................................................... 14.0
  3. Tom: I did see that assertion in Ceramic Science For the Potter. I'm not buying it. :). Also, he's talking about kaolinite, NOT a working clay body, which includes very non-plastic materials as well. The proof is in making a side by side comparison with gelling and non-gelling bentonites both in pure clay and in an actual clay body. I have done that, and gelling is better in my experience. I DO think you could add far more calcium bentonite in a clay body than you could sodium bentonite, but I haven't tried that except for that one test with sepiolite (non selling magnesium smectite).
  4. First, on the general format of this "media", which I have never participated in before. Is it more clear to "quote" and respond, or just let her rip? Anyway. The shrinkage. Yes, 17% is manageable, but remember that is at cone 05! In the meantime, I am trying to get larger (50-pound sacks) of sepiolite and bentonite from the mine in California, which has since been sold to a large multinational corporation. These people really do not want to deal with us. I did order a 50-pound sack of "calcium" bentonite from "Millwhite Inc", in Texas. Apparently, it's on its way. I am going to do exactly what you suggest, add a lot of it, say 15% to 35% kaolinite, 30% silica and 20% feldspar and see what happens. How to tell calcium bentonite from sodium bentonite. If you look at the formula, the calcium bentonites will have more calcium and less sodium. Often the calcium is just impurities of calcium carbonate, not tied up in the clay crystals. I have never noticed any impurities of sodium, what could that be? Calcite is abundant everywhere. Maybe a rule of thumb is if it gells it's sodium bentonite and if it does not it is calcium bentonite. That seems to be what we are interested in any way. Maybe the conversation is really about gelling and not gelling? Magnesium in some of these smectites (hectorite and sepiolite and attapulgite) could have a detrimental effect on HIGH fired clay bodies, but I don't think that would be a problem with low fire bodies. "bentonite" by definition does not have magnesium, at least not in the clay crystals. Speaking of attapulgite, I ran across a commercial additive called "acti-gel", which is apparently attapulgite, very similar to sepiolite, magnesium based. I sense we three agree on one thing: the small particle size of "smectites" deserve more investigation as to including in a clay body both for that property alone and for improving "plasticity". Again, let's do it! Apparently, we are not in agreement on that gelling thing. And about "gelling". A clay body is not kaolinite alone, it has the gigantic particles of silica and feldspar or powdered rock, which are generally not plastic at all. Here's a test about improving or creating plasticity of those materials. Take 500 grams of silica and add 100 grams of both a gelling smectite and a non-gelling smectite, and see which mix is more plastic. Drilling mud in oil fields. Yes, sodium bentonite's primary use is drilling wells. There are many other well drilling chemicals that may be of use to us potters. I live near Bakersfield, California, which is the oil hub of California. A couple years ago I got a 50-pound sack of "poly-anionic cellulose", which works exactly like CMC, except better, at about 1/10th the price. I would go back, except they will not allow me to haul anything away in my van, they will allow, they insist on a pickup truck only. Fascist Company Rules. So one of these days I'll borrow a pick up truck and drive to Bakersfield and try to figure out what they have. They DO have a sodium bentonite with a chemical additive that apparently makes it gell even more, I think with the term "methacrylide or methacrylamine" in it. Drilling mud construction is an art and science of manipulating the rheology of a well bore. We are trying to do the same thing in a clay body, right?
  5. Curt: I went back and more carefully read the previous posts. The idea of adding calcium bentonite to a clay body for "packing" purposes, to make for a better clay body, regardless of any improvement in "plasticity". Let's try it! The clay mine I mentioned near Death Valley also mines a mineral called "sepiolite" it is a magnesium silicate related in some way to talc, and possibly asbestos. I think. I experimented with it also, and made a low-fire, cone 05 clay. Extremely small particle size also. it does not gell, and I could not get it to gell by any additions. The cone 05 clay body threw amazingly well at about 30%, I have notes somewhere. It shrank a lot, however, maybe about 17%? I made one attempt at a glaze that fit it, soaked it in water, etc, it does not lose its ring, appears quite strong. It is porous, but don't remember a number, but that could probably be manipulated. So if that kind of addition seemed to work with sepiolite, why not calcium bentonite? And there is a lot of calcium bentonite all around the world. I'm going to try it. Thank you.
  6. Curt: How to tell calcium bentonite from sodium bentonite. The vendors should tell you that! They don't. I read at least one article, from a European clay journal sort of addressing this. The issue was is it proper to call a "sodium activated calcium bentonite" a "sodium bentonite"? The answer according to this journal article is yes, it is proper because really all bentonites are essentially the same mineral, and there should be no distinction whether or not this placement of the calcium or sodium is by human artifice or natural. My guess is that most vendors are not aware of the difference between calcium and sodium bentonites. If in doubt, I would order a small amount and check it or maybe ask. I believe the advantage of calcium bentonites is that they tend to be much lower in iron than sodium bentonites, and therefore more suitable for white or light firing clay bodies.
  7. Tom (and all), I routinely do the following test on clay bodies. (1) Determine the mixed consistency of a plastic clay body at it's best, not too wet, not too dry, as plastic as it can be. (2) make a test bar, at least 100 grams and weigh it. (3) Dry it out completely (4) weigh the completely dry sample. So the wet plastic sample contains "x" amount of water, plus the later measured dry weight. Usually, the water is about 20% of the wet plastic weight in my experience, or add 25% water to the dry sample for the "average" plastic clay. 4 parts dry clay body and 1 part water. About. I have never systematically looked into what this ratio is with and without various bentonites and clay body recipes. That would be interesting to know. I fire to cone 10, and all the tests in recent years are cone 10.
  8. Hey, I'm loving this! Curt (and all), I did not make any changes to either Hectalite 200 OR any Wyoming bentonite, but not for lack of trying. I added small amount of lithium carbonate and additional sodium carbonate, with no changes to the behavior of either. The only changes that took place was with the two"calcium bentonites" I experimented with, Bentolite 10-L and a local material mined near Death Valley, California. Both became dramatically more viscous with additions of 3.5% sodium carbonate OR 2.5% lithium carbonate. I tried potassium carbonate on all of the above, with no effect at all. Yes, I also tried calcium bentonite (the two mentioned ) AND sodium bentonite (activated and "natural") with many different clay bodies, including different recipes with EPK, #6 tile, McNamee, Grolleg, Standard, several samples of kaolin I imported from China, New Zealand Ultra Fine, several ball clays, and some mixtures of these. Sodium bentonite, either those I "activated" or natural made for a better, more workable clay body. I would also make a coil about 3/4 inch diameter (2 cm) of the samples check for plasticity. The "short" clay would crack where bent. About Lithium carbonate. These experiments started with me noting that hectorite has lithium oxide in the chemical structure of the clay crystals. And hectorite is the mother of all gelling bentonite-like substances. So, I on a lark added some dissolved lithium carbonate into a liquid emulsion of various true bentonites, and this addition to the two calcium bentonites completely transformed them. So I took to the internet and discovered this phenomenon of "cation exchange" had been patented in about the 1930's in Germany, and there had been at least one description of using lithium carbonate, quite recently, in a journal in China. My observation is that lithium carb makes for a more viscous clay, and improves clay body workability more than sodium carbonate at equal additions to a clay body. The figures of a 3.5% addition of sodium carbonate and 2,5% lithium carbonate was arrived at by trial and error, based on the degree of viscosity change. I believe the term is "titrate". At the point where no more visible change was evident in viscosity, I backed off and used LESS, until I arrived at what I thought was the minimum amount that caused this change in viscosity (gelling). Kind of subjective.
  9. And Furthermore. Clay scientists, although we may want to think of them as closet potters working as scientists for the money, probably don't know squat about what it takes to make a good throwing clay body. Hey, it's important to US, but to very few others.
  10. Well, I was delayed. So if I understand you, you are saying that if you use CALCIUM bentonite in a plastic clay body, at first it will seem short, but if it ages for a few days it will become plastic. And if a SODIUM bentonite ages for a few days, it will become soft? My experience is that porcelain (I'm only talking about porcelain because that's the only clay body I've experimented with, well, not entirely) with either sodium or lithium activated calcium bentonite, AND standard Wyoming (sodium) bentonite, AND Hectorite (Hectalite 200 or Macaloid-a sample from before they sold out to Bentone) will NOT soften or become less workable after aging. My experience is that it (clay with sodium bentonite or hectorite) becomes MORE workable. I probably have in the past allowed a sample with calcium bentonite to age, but I just don't remember what happened regarding workability. I'll sure give that a try. You are talking about "Ceramic Science for the Potter", about particle size? I'll look that up later today. Here's an interesting tidbit. I use Plastic Vitrox "clay" in my current clay body. The word "plastic" is a little of a misnomer. I also use it to make throwing bats, but it (PV) shrinks, which helps cause the bats to warp a little. So I calcined 10 pounds of it at cone 05, and it was STILL plastic, such as it is. And it is pinkish tan/brown! Also, it seems to "loose" water more easily, and so far it has helped with the warping. But it still shrinks, just not quite as much. I think it might have something to do with the shape and/or particle size of the PV, which maybe doesn't change firing to cone 05. Don't really know what is going on there. About Neph Sy, YES, I hate it in a clay body, mostly because it becomes so thixotropic when it sits around a while. I knew it releases soluble material but had no idea it was in the neighborhood of 18%! It does make sense if the soluble portion migrates and concentrates itself it would outgas more vigorously. I do not really use Macaloid, but thought it was sodium hectorite. It is now called Bentone something or other I think, changed owners more than 10 years ago. I have gone to that area many times, and once went to the office in Newbury Springs and the lab gal gave me samples of stuff. I do know Hectalite 200 is a natural sodium hectorite with considerable CaCo3 in it, on the order of 20%. That calcium is not in the clay crystals, it is just a contaminant of calcium carbonate.. Macaloid probably has the same contaminant, but I believe they refine the bleep out of it and get most out. I would need evidence before I accept that Macaloid/Bentone is a calcium hectorite rather than a sodium hectorite. Actually, I do not believe I have ever held in my hand a sample I KNEW to be calcium hectorite. I spoke to an American Colloid salesperson before I wrote that CM article and he said Hectalite 200 was mined in the wilds of Nevada, "Superstition Mountain" I recall, not near Newbury Springs. They might have mined a lot of it and squirreled it away, maybe in South Dakota or somewhere. At least then, they were not actively mining it, the salesperson said. It is a naturally occurring sodium hectorite that they just grind to a powder, That's the one I use. I take into consideration the calcium carbonate in the material. The guy at American Colloid said sodium hectorite was formed in the oceans millions of years ago, and calcium hectorite was formed in fresh water. Even though they differ in sodium and calcium, they do share the Ii20 and magnesium. The lithium angle is what got me going on activated bentonite. I figured if hectorite had lithium in it and it was so "plastic", why not add lithium carb to bentonite and see what happens. And Lo, when I added it to Bentolite 10-L, calcium bentonite, it gelled like sodium bentonite. With bentonite 325 (sodium) it did absolutely nothing. I thought I had made a momentous discovery until I checked The Google and found out industry had been doing this for 80 years. I'll look forward to your response when I return.
  11. Hi Tom Thank you so much for res[ponding. Right now I am taking an opportunity to go up to my studio and home for the first time in 3 weeks.. My wife and I are taking care of her mother, and normally we have people coming in to help, but, things happen. So I've got to go. And no internet service where I "live". But I WILL be back. As you might be able to tell, I am VERY interested in this subject, not only bentonite, but clay "plasticity", and all the tricks involved with that, and yes what is plasticity anyway. And all that, how it is related to glaze, etc. So please be patient. Ray
  12. I wrote an article in ceramics monthly about cation exchange for the two calcium bentonites I mentioned, https://ceramicartsnetwork.org/shop/ceramics-monthly-pdf-september-2014/ . I read several patents going back to the 1930's in Germany about that, and some other sources about cation exchange of calcium bentonite, and that is what the article was about. Regarding which of the bentonites, calcium or sodium, produces a more workable clay body, here's a test. Make two clay bodies, identical except use 3% calcium bentonite in one and 3% sodium bentonite in the other, with the same weight of finished clay, and the same stiffness. Say, 30 feldspar, 30 silica, and 40 kaolin, not that this is an ideal clay body, but it will show up the effect of the bentonite. Make a pot with each. Dollars to doughnuts the clay body with the sodium bentonite will be far easier to throw and will hold up better to the process. That has certainly been my experience, repeatedly. When most potters say "plasticity" we mean a clay that is responsive and does what we want it to do. This may differ from the strictly technical meaning of the word, maintaining shape upon deformation. They BOTH maintain shape on deformation. Wow, I am sure glad I came across that post. Very much looking forward to your response. I'll go look up your article right now.
  13. I have tried as much as 5% calcium bentonite (Bentolite L 10 and one from LMV Nevada), and found it does not help workability/plasticity at all, unless activated with soda ash or Li2CO3. The green packing property , because of the tiny particle size, might make for a tighter clay body, and you maybe could use far more calcium bentonite than sodium, but I haven’t tried that, above 5%. I recently ordered a sample of Bentolite H from (KYT?, formerly Southern), and Millwhite, Brownsville, TX. 8 bucks a sack. But with the idea of activation, cation exchange. Sorry for the delay here, but I was just looking for information on bentonite and stumbled on this. Hope someone finds it.
  14. Sequoia Pottery

    Attaching Dry Pieces To Each Other

    This has been a while, if anyone is still paying attention to this: Recently I ran across an old patent about attaching dry ceramic objects together, like a dry handle to a dry mug. Now I can't find it! Here is the process as I remember it. (1) "machine" the two objects to fit as closely as possible. (2) Brush the two objects with a generous coating of 4% solution of polyvinyl alcohol and allow to sink in. (3) mix a slurry of clay body with the 4% solution of pva, coat both objects to be joined, press them together, and ...voila. I routinely use polyvinyl alcohol on regular mug handles and it seems to work very well, but have never tried it dry. Does anyone have experience with this?

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