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About glazenerd

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    Clay Research

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    St. Louis, Mo.
  • Interests
    Crystalline glaze chemistry. Been stuck in clay chemistry and formulation. Writing formula limits for porcelain, stoneware, and low fire bodies. Developed new cone 04 colored porcelain body, cone 6 porcelain, and cone 10 bodies for public use.. 60yrs old.

    Email: optix52@aol.com

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  1. Curt: Short abstract on three sodium bentonites, and the effect of PH on each. You will find the summary intriguing.( bottom of page) https://www.ncbi.nlm.nih.gov/pubmed/10502376
  2. Gokul: Here is a link to some chemical analysis of your laterite clay. The only one I have been able to find from a reputable source: after two weeks of looking: http://sciencejournal.in/data/documents/SCIENCE-VOL-1-2-3.pdf. You will find a table on page three. Glad you are the production manager at this clay company, and not me. From what I have read thus far, India has some very unusual clay composition: very much different than Western clays. Combined total of alumina and iron is over 60%- wow! No wonder you cannot fire over 900C. If the duty taxes and tariffs were not so high, I would suggest importing a fix: but that would be very costly. Still digging around for local resources, which seem to be very limited.
  3. glazenerd

    pugmill - Bailey vs Peter Pugger

    I own a PP VPM 20SS. For studio work I could see the advantage of having the vacuum in the nozzle. For production, the PP pugs out nearly double in the same amount of time. I talked to the Bailey people: friendly, knowledgeable, and a good reputation. I think either machine will give you good service. The question to me is: how much clay will you use and at what rate? Do you need 25lbs at a time or 45 lbs? Ease of cleaning was one factor for me. Either machine will give you good service. T
  4. glazenerd

    Porcelain Clay Bodies

    Porcelain typically runs 70-72% silica, 17-19% alumina for the target of 4:1 si/Al ratio. ( mr. Ron Roy). Porcelain usually has 50% more flux than stoneware; which is where the plucking comes in. Cone 6 stoneware runs 2.89 molar alkali and porcelain averages 3.89 molar. The more translucent the body: the higher the alkali molarity, which also translates to higher COE values. Vitrification comes with a price: plucking being one of them. T
  5. glazenerd

    Choosing Glazes

    Part of the cycle of life and the road of discovery. Every potter is influenced by pieces they see; rather it be form, technique, or glaze. Just as every potter yearns to find their own voice; rather it be form, technique, or glaze. Personally I do not question why a certain potter influenced me; but rather why I was drawn to it in the first place. It is the initial attraction to a piece that defines your artistic/ creative drive, the person who made it is secondary. Pottery is a curious mixture of art, creativity, and skill sets. Artistic expression matures, just as people do with the passing of time. Exploring the boundaries of form, technique, and glaze is part of the process of finding your voice. Replication and duplication of the pieces you admire is part of finding your own voice; but interpretation is the sign of personal expression. Enjoy the journey. T
  6. DM thank you for your kind words. I am in good company, this forum has a wealth of people with differing expertise. T
  7. LT: chapter six is an interesting read. The thermal shock tested on aluminum rods got my attention. Alumina ratios have been on my radar for sometime. In an earlier chapter, a recommendation for using a microscope with polarized light source was made: answered another question I had. The opening phase change diagrams confirmed some thoughts as well.
  8. Mixed up 200lbs.,CR2 cone 6 porcelain: let the crystals begin. Going to mix up 50lbs., of cone 11 "wood fire" porcelain next weekend. Tested the cone 11 last year: does strange things :) 

    1. yappystudent


      More power to you. 

  9. Gokul: Spent the last week reading up on your red clay-laterite. I find the chemistry of this clay very intriquing: unlike typical Western clays that have defined reactions. The most compelling insights came from a study done by The British Ceramic Society, which used the term "cementing" to describe the properties. This term was used to describe its properties of wanting to compact into a dense ball. The 5-14% iron content! along with 30-35% alumina , coupled with the acidic nature; is creating its natural resistance to the usual plasticity fixes used in formulation. In plainer terms, by nature it wants to flocculate ( heavily). The solution may include using a high alkaline negative ionic additive. Calcium is an important part of this puzzle because of it cation exchange rate. Sodium has higher cation exchange values, but calcium actually exchanges ions at a rate 200 times higher than sodium. Which I why calcium bentonite works better thn sodium bentonite. https://trid.trb.org/view/884695. This short abstract defines some of your issues. If you look at India's natural resource maps from the Dept. Of Mines: you will see a very small region where high alkaline clay deposits are found. India has very little deposits, as compared to the West. You need to find a supplier who mines in this area. High alkaline ball clay will be lower in alumina, lower in iron, and richer in calcium: all of which you need. Your ball and red clay are approaching kaolin in alumina content: an oddity of itself. You are dealing with high iron, high alumina, acidic, and high carbon content clays. Having any one of these four require special formulation practices: but you have all four. A very tough problem indeed. tom
  10. Hi Malinda i know from your previous post, you live in a region where laterite clay is used in the brick and roof industry. Laterite is an unique clay type with its own specific chemistry, not commonly found elsewhere. In fact, using it as an engobe over another clay, or using a different engobe over laterite simply will not work. The chemistry required to overcome laterite properties is complex. Wish I had better news for you. nerd
  11. Why? Because I find it strangely curious that glaze had exacting standards and defined chemistry. In my early searches for information about clay chemistry, none existed. Yes, some boundaries had been defined, but formula limits, plasticity parameters, and particle distribution was a loosely defined concept. If I would have not seen a crystalline vase in Williamsburg, Va. In 2007 I would have bought a lathe and made furniture. But alas, I now have my rabbit hole decorated, and there is plenty of brain candy to munch on down here. I did talk to Alice yesterday, she has not aged a bit. Nerd
  12. Gokul: Did some chemical research on laterite; and am coming to the conclusion this problem requires a chemistry solution. Laterite is formed as silt in active river beds, under highly acidic conditions. The acidity strips away negative ions such as calcium, sodium and potassium. As they dig through the layers, the levels of these ions are depleted: which explains the zero calcium analysis. The next problem being iron, magnesium, and nickel are found in much higher levels, and usually as salts. The final issue is that hematite has anti-ferromagnetic properties, including on a molecular level. Which in this case has an effect on plasticity, seeing as though plasticity is based on negative ionic repulsion of adjoining clay particles. Hematite directly interferes with that molecular activity. Laterite is so high in alumina, they use to process pure aluminum from it. So in pottery term; your red clay has every property that hinders ionic exchange: which translates to every possible anti- plastic property you can encounter. Oh joy!!!!! If you have a PH meter available, I need to know the PH of your pugged clay. That will tell me what minerals to add to overcome the lack of ionic ionic exchange. I think that is the root cause here: lack of ion exchange. No exchange = no plasticity. Secondly, I need a chemical analysis of your ball clay. Your process is fine, the fact that you filter press and still have plasticity issues astounds me actually. At this point, I think you need 0.50 to 1.00% barium carbonate to deal with the scumming and break down the soluble salts to start. After that, probably 1-4% calcium carb to replace depleted negative ions and to counter the acidity of this clay. You will have to a do a series of 1000 gram test batches to figure this out before you commit to production. I do believe the positive ionic composition of this clay is causing the shredding seen in your pics. Very odd and curious clay issue; but challenges intrigue me. Nothing like a good puzzle!! Tom
  13. Gokul: I would need more details about your processing and formulation before I could make determinations. I can see things in your latest pictures that concern me. The first being color streaks: which suggests that materials are not being blended thoroughly. Are you dry blending all materials before you mix? I can see surface blisters, which I I'll assume is air pockets? I know de- airing equipment is not readily used in your area. From reading Dr. Sutharsan,s study, the laterite is mined from under water, and used pretty much as is in the brick and roof tile industry. Given the hematite levels, along with calcium, sodium, and fluorite content; it vitrifies without any additional fluxes. So I will also assume you are just adding 1% bentonite to the powdered form, without any other additions? As I also know your red clay does not appear red until it oxidizes because of the hematite. One of the big issues is the sesquioxides, which make up nearly a third of this natural clay. To give readers an idea of how these react in a clay body: imagine blending alumina and grog together, then trying to make them bind together in a malleable ball. It would be the same as throwing 30% of beach sand in a clay body and expecting it to hold its shape. Western clay formulation practices are not going to work in this case: you are dealing with a very unique clay variety, that has its own unique chemistry. i know ball clays are available to you, and I would personally be exploring that avenue. I would start with an 80/20 blend of red clay and ball clay, and skip the bentonite all together. I realize 20% ball clay is on the high side, but you are dealing with a silty/ course clay. However, the particle size, CEC value, and WOPL of the ball clay you select , will ultimately determine the recipe %. If you do not have the capacity to dry blend before mixing, this will be problem as well. Not much more I can add, I am sorta shooting in the dark without knowing the specifics. Tom
  14. Gokul: just finished reading an abstract from Dr. Sutharsan: PHD physics from Annamial University. Apparently India has its own unique clay chemistry due to the subtropical weathering of silty clays. Your red clay is laterite: very high in iron and alumina: higher than those found elsewhere. Secondly, the iron content comes from hematite, and not pyrite: which is good news in one sense, bad in another. Dr. Sutharsan ran thermal analysis on your red clay: quartz inversion occurs at 560C, and more importantly was his report of an exothermic reaction at 991C. He reports this temperature as the spinel/ mullite conversion temperature. In plain pottery terms: the temperature at which vitrification begins. Bisq firing to this temperature would be problematic because the porosity of the body is beginning to close: so shivering issues could possibly occur. The peak firing temperature of your red clay is 1100C. particle distribution reported as 45 um to 90 um. Rather large for red clay. Your ball clay is of the silty alluvial variety; also much higher in alumina than found elsewhere. Oddly enough many deposits reported no calcium content: which plays a role in plasticity. After getting some background on your clay types: I would start by doubling your plasticizer additions. (4% bentonite) Secondly, you will not be able to follow the typical firing cycles and peak temperatures used commonly elsewhere because your clay varieties have their own unique chemistry, not found elsewhere. Lastly, Dr. Sutharsan specifically recommended the red clay not be used in ceramics due to its high iron, alumina, and particle sizes. I believe you can use it, but you will have to develop your own customized formulation criteria to overcome its properties. Other articles reported spikes in the iron content upwards of 8%, which I suspect is what has happened here. Tom
  15. After studying these pictures for a month, I have narrowed down my short list. Picture 1 indicates a short clay, more specifically a red clay with high levels of sesquioxides. This type of clay resists water absorption, as the standing water indicates. If this clay is used as 50% of the recipe! you will need to increase plasticizers by a fair amount. Picture 3 is the most telling to me. I can see three distinct and seperate issues that add up to serious cracks. Again, all three trace back to the sesquioxides; specifically FeO3. The rim is the usual terra cotta, but the base is turning red. This would mean high iron content, combined with iron reduction. (Yes, I know you fired in oxidation.) The sulfides in the clay were heated too quickly, thereby reducing the iron. The iron level is high enough to cause brittleness as well, part of the explanation for cracking. The third problem, caused by high iron as well: is cristabolite inversion. Many potters know about quartz inversion, but cristabolite inversion causes 2-3 times the stress on fired pieces. Any potter who has heard "pinging" sounds coming from their kiln while cooling (200C / 392F) knows about cristabolite inversion when they opened it to find crazing issues. In your case you have multiple issues happening at the same time, but all stemming from high iron content. The red clay is causing the problem. It has either changed chemically as they dig through the mine, or your recipe addition is too high. Secondly, this same red clay has high levels of sesquioxides that require much more plasticizers. The black spots on the rim in picture 2 looks like possible coring issues: also iron (disulfide) related. Finally, high iron can also elevate cristabolite formation: which likewise makes the fired piece brittle and susceptible to stress cracks. My best educated guess from looking at pictures. I would take a hammer to the bowl, my guess is you will find coring issues. Tom

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