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About glazenerd

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    Clay Research

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  • Location
    St. Louis, Mo.
  • Interests
    Crystalline glaze chemistry. Porcelain, Stoneware, Fritware, 04 Colored Porcelain clay research & formulation.
    Ceramics Monthly Articles: Jan. 2018 Cation Exchange (plasticity), April 2018 SSA Clay Formulation, May 2018 Bloating and Coring.

    Email: optix52@aol.com

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  1. glazenerd

    EPK vs China Clay

    Mary: two primary differences in kaolin. The first being particle size, although at cone six and above enough flux will do the job regardless. The second: titanium content. Kaolin is very low in iron and magnesium, but can have low ( china/ grolleg) to much higher levels: EPK, tile #6, helmer. White means low titanium, buff to light tan indicates titanium. T
  2. glazenerd

    Brown Slip warping and cracking?

    Bear: your recipe in whole numbers: Redart 55%, kaolin 14%, silica 11%, kyanite 10%, HTP 6%, spodumene 4%, bentonite 1%. Analysis: total KnaO 2.71, total flux 4.58%, iron 1.86%, silica 76.15%, alumina 16.77%, SiAl ratio 4.54 est. COE 5.45 2.71% molar KnaO (sodium & potassium) too low for cone 7. This recipe is depending upon the natural fluxes found in the Red Art, kaolin, and HTP. Bentonite is not required in this recipe because the HTP has a high CEC ( plasticity) and finer particle size. Kyanite forms elongated mullite needles that add strength, but they do not supply the structured glass phase required. 4% spodumene I assume was added to lower expansion, it does not supply enough flux to promote a melt. From the analysis, this is a modified cone 10 recipe. I believe the warping stems from the kyanite and cracking from the lack of glass phase. Redart 50%, kaolin 20%, silica 6%, kyanite 5%, HTP 8%, spodumene 4%, bentonite 0, Kona F4 7%. Anaylysis: KnaO 3.40%, total flux 5.29%, iron 1.74%, silica 74.96%, alumina 17.34%, SiAl 4.32, est. COE 5.69 When formulating stoneware recipes, rather throwing or slips: one principle has to be observed. There has to be enough KnaO available to melt the silica. Typically stoneware recipes have a minimum 10% KnaO additions to ensure that silica Is incorporated into the melt. Any free silica converts to cristabolite, which destabilizes the structural strength. Have you heard pinging come from the kiln in the 400F range? That would be cristabolite inversion. It can cause the micro fissures you describe as well. I tried to keep this in line with your original recipe, but personally I would go 10% Kona or equal, and reduce the silica to 3%. Reducing the silica into the 72% range would not hurt. tom slips have differing particle packing densities than clay bodies. How you mix, how quickly you pour afterward, deflocculants all play a role in collidial chemistry.
  3. glazenerd

    Varied Perlite inclusion results

    Charles: clay and minerals are constantly subject to environment in which they are deposited. The term is morphology. The parent mineral formation, subjected to other minerals in its environment, weather conditions, and time = final material composition. The perlite in the USA can have higher natural fluxes, than perlite in Aussie. The clay you use may have higher flux content than the clay used in Aussie: both effects outcome. A forum member was kind enough to send me a sample of clay she found locally. The natural conditions produced over 20% flux content: so much so, a white film was visible. Months ago a clay plant manager from India contacted me about clay issues. The acidic conditions of that region had stripped nearly all natural fluxes from the clay. Much depends on environment as well. t
  4. glazenerd

    Clay contamination

    Clay(s) have various levels of organics, normal. Organics can produce fungus and the familiar smell of decomposition. t
  5. glazenerd

    Brown Slip warping and cracking?

    Bear: several things wrong with this recipe, from a clay chemistry stand point. The first being: clay recipes do not require that type of precision in weight measurements: that appears to be a carry over from glaze calculation. There is zero difference in outcome if you use 55% Redart in lieu of 54.8014..%. When using plasticizers such as macaloid or V-Gum T: 1/2% additions become necessary because of the properties of these types of materials. this recipe is depending upon kyanite to produce mullite, in lieu of the typical glass melt feldspars produce. Kyanite converts to mullite when you get into the cone 5-6 range: and is thought to produce better strength because of the elongated needles that form. Typically 3-5% is added for additional strength, but it is not used as a primary glass former. spodumene supplies lithia: which is used to control thermal expansion properties of a clay body. Oven ware bodies, with very low COE index, use spodumene almost exclusively. Sodium and potassium for example have individual expansion indexes ranging from 90-100 ( round figures), and spodumene is roughly 1/3 of that. However, it takes a fair amount of spodumene to supply enough lithia to form any kind of glass phase. Bentonite is probably being used in a two-fold purpose: as a plasticizer and to supply extra fine particle distribution. More likely than not, this is sodium bentonite which is subject to swelling and high water absorption. (Absorbs up to 15 times it's weight in water.) used as a suspension agent in glazes, but does not supply the same effect in clay/slip recipes. If you are going to use it: better to blunge it in a slurry before adding to the slip. Dry additions do not distribute very well in clay bodies. As a general rule of thumb: kaolins supply 37% alumina and ball clays 25-30%. Clay formulation typically aims for a 4:1 SiAl ratio. Unlike clay bodies formulated for throwing: slips should be on the low to medium plasticity level. You have other issues going on as well, but will let you update the info. t
  6. glazenerd

    Hudson River Clay

    Mary: the hot dunk is just a preliminary test to check for crazing and in this case: shivering. There is a more formal test, but I do this as a "quick" check. In essence, checking stability. I mix all of my own clays: but in the pics above: a very clean white stoneware. Actually I have two shelves full of my early " learn to throw" pieces; good for testing or the landfill. This perticular clay/slip falls into the abyss in regards to glaze chemistry and/or clay chemistry. All I am doing at this point is stabilizing: as in no shivering, while maintains a full melt. Typically, a glaze has a maximum of 20% clay content! more often between 3-10%. So in dealing with 50-75% clay content, it gets interesting. every clay variety you fire this on is going to change the color. < insert lengthy chemistry discussion here>. T
  7. glazenerd

    Orange Red Iron Glaze

    Mary: as DW pointed out, there is chemistry involved. That said, how FeS2; the most common iron source in American reacts, and how FeO3 (hematite) reacts, and how FeO4 (magnetite reacts are all different. Before my fellow potters chime in and state the obvious: all iron reduces to FeO- that is not what I am referring to. My point Mary, Hudson has magnetite; and the final colors will not result in the old Albany, or Red Art, or Newman Red. t
  8. glazenerd

    Hudson River Clay

    Both of these are 50% Hudson, 20% potash, 5% lithium, 20% silica. Added titanium to one of them. Did the job of melting, but the potassium created some pin hole issues. Will need a hold at peak. I took them out of the kiln at 350F, and plunked them into cold water- survived well enough.
  9. glazenerd

    Hudson River Clay

    Mary: calcium bentonite is also abundant along the Hudson. Magnetite (iron) will present itself dark grey to black in sedimentary deposits. Plenty of mica and calcite around the Hudson as well. When I was candling some of the material, got that musty aroma of humus as well, albeit very low %. At this point, my prime suspects in your Hudson River clay. arsenic is a normal by- product of natural oxidation/reduction of iron, especially magnetite. https://pubs.acs.org/doi/abs/10.1021/es702625e Tom
  10. glazenerd

    Hudson River Clay

    Think I found the cause of 8.31% iron content: https://thediggings.com/mines/usgs10296653 mostly magnetite mines along the Hudson.
  11. glazenerd

    Hudson River Clay

    Gred: oyster shells would provide calcium, not sure what else? The iron and magnesium levels are the highest I have seen in natural clays: not sure what the contributing factors are, but working on it. I originally thought the iron was hematite due to the color, but from reading; magnetite is more common in NY. Later this year I will demineralization a sample and have a look. I am fairly confident it is a combination of calcium bentonite and smecite montrollites. The old Albany slip was classed as non-plastic; this sample is highly plastic- approaching macaloid in nature. Interesting indeed! Tom edit: I will look into the iron levels in oysters
  12. glazenerd

    Hudson River Clay

    Mary: was reading several pieces on mineral resources found in NY: one referenced Cherry Hills. Might have read it wrong; might be an old mine? I could not find it either. Tom
  13. glazenerd

    Hudson River Clay

    Mary: been doing some research, trying to figure out your clay. calcium bentonite is found in your area. Calcite is mined and abundant all over NY state. More interesting, smecite is fairly common in the Arirondack Mts. Even more interesting is how it is formed: humus is drawn into existing illite deposits on the forest floor and is converted over (much) time to a smecite variety. Even more interesting, native NY smecite has a green/ gray cast: which I saw in your samples. The specific native NY smecite is 0.5 um particle size: in pottery speak 2500 mesh plus. Question: how far away is Cherry Hills? And it's proximity to the Hudson? Tom
  14. glazenerd

    What Is Ceramics, Is It Art?

    Perhaps the Moody Blues should have titled their 1969 album " In Search of the Lost Clay." DESTINATION: being defined in this topic as the pinnacle of success in forming, glazing, firing, or technique. that said: some people enjoy the journey (me) to that destination as much as arriving there. Others want to reach the destination as soon as possible. T
  15. glazenerd

    Cone 6 Red Stoneware Recipe

    Tin: mostly because potters try to doctor up lizella to get it to seal up at cone 6. Lizella has some percentage of chlorite minerals ( green cast.). The iron is lower than the more common clays such as red art and Newman. Greenstripe tends to bloat easier than most. you are trying to customize a fired color: which can be done. You need to do samples at 30%, then 40%, and 50%. Once in you get into your color zone, the 5% increments. 35% etc. tom

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