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glazenerd

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About glazenerd

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    Clay Research

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    Male
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    St. Louis, Mo.
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    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

    Slip reclaim

    As a point of interest: what are you using to defloc? T
  2. glazenerd

    What Is Ceramics, Is It Art?

    "The tendency towards individualism, which has resulted from the declining economic importance handcrafts as a means to fulfill everyday functional needs, has placed pottery making in somewhat the same position as painting and sculpture." excerpt from: Stomeware & Porcelain by Daniel Rhodes 1959
  3. glazenerd

    Shrinkage isn't consistent

    Hero: the first firing had 20 mugs, and the second load 120 mugs: this difference alone plays into the equation. ( thermal mass) Mark hit the key points, no need to rehash. the cooling cycle affects glaze, does nothing for the clay. In cone 5-10 firings ( clay bodies matched), clay begins to vitrify at 2050F. From 2050 up to 2195F is when clay develops. A kiln loaded with 120 mugs needs to be dialed back to 108F an hour ramp climb to ensure vitrification and even distribution of heat. Large kilns have hot and cold spots: slowing the final ramp to peak will help level out this issue. Using cone packs to ensure you have reached peak is also advisable. From your comments about a controlled cool: I will assume a programmable controller? If so, common for the thermocouple read out and actual kiln temp to be off ( by up to 40F) using cone packs to calibrate your temp read out is necessary in a production setting. Read TC (thermocouple) offset in your kiln manual. Peak temperature will effect shrinkage in a cone 6 firing, with porcelain being more susceptible. T
  4. I only sell WALL tile and I do carry "all perils" liability.
  5. Before it was called flame ware/ovenware- for decades it was called lithia ceramics. T Insurance...liability...exposure... More reasons I only sell tile.
  6. Porcelain / white stoneware on page 1 Dark - red bodied on page 2 Tom
  7. Jason: 4 primary considerations when selecting a firing schedule. 1. Functional of non-functional use. You have a lot more freedom if non-functional although there are still limits. 2. Bisq fire or single fire. If starting from bisq, you can fast fire up to 2050F, then either 108 or 125F an hour to peak (cone 5-6). Assuming proper bisq firing has been observed. The slow ramp from .2050 to peak is allow spars to off gas and to allow heat to reach the core of the body. If single fire, some variations pending porcelain, white stoneware vs dark or red bodied clays. 3. Large, heavy wall, or sculptural pieces need special consideration. Mugs, bowls, yarn holders etc can fire on medium up to 2050 without issue in a single fire. Wall thickness over 3/8", large foot rings, large surface contact, or just heavy needs to go on slow speed to allow for heat work. Quartz inversion becomes an issue (1063f) can crack or split large pieces. 4. Speciality firings such as raku, salt, wood - all have their own schedules. Not going to address any of those: not my area. Marcia Selsor and several others could certainly expound. Rather you single fire or start from bisq (observing rules for dark/red bodies- high iron) and also observing quartz inversion ramp for large or heavy pieces: once you hit 2050F, slow ramp to 108 to 125 to peak. Potassium starts melting at 2112f and sodium at 2144F is an additional reason you slow down at 2050F to allow these spars to off gas completely. Tom
  8. 108f an hour from 2050F to peak is the soak. Intended to mature clay, but has the added benefit of flattening glazes. The glaze is in direct contact with the kiln temp, it can take an additional 30 minutes for that atmospheric temperature to reach the core of the clay body. 50F an hour is not necessary. T
  9. Jason: Orton developed his firing schedules from research he did on firing clay bodies ( various types ) in lab controlled studies. So "myth" would not be an accurate term. The 108F per hour ( slow cycle) came directly from his research on organic and inorganic carbon burn out phases found in natural clay. InOrganics burn out by 1000F roughly, and in organics burn out from 1250-1750F. Inorganics include lignite coal particles and sulfides, primarily from iron disulfide. West, Brown, Ougland, Brindley, Lawrence (PhD's) all confirmed his findings from the 1950 to 1970's. Orton did most of his research in the 1920's. The Orton cone schedule is based on this research: it was developed to mature clay: not glaze. The focus on firing schedules to mature specific glazes is a modern trend of the last 20 years. The 2050F I recommend in my firing schedule also comes from studies done in the USA, France, Brazil, India, Germany, and China ( a University Studies) which all confirm an exothermic reaction (releases heat) at 2050F. Clay bodies absorb heat ( endothermic) up unto that temperature, the most notable being quartz inversion at 563C. The clay body is actually porous and expanding until it hits 2050F, and it begins to close up as glass/mullite develops. Better known as the metakaolin to spinel phase change. At 2050F up to 2190F when feldspars are most vigorous: both produce gas as they melt. The 125F that I recommend is to allow spars to off gas before the body becomes too compact, and to allow additional time for spars. Most modern pinhole issues come from clay body issues, not glazes. If you are using dark or red bodied clays: then 108F an hour is advisable through the entire cycle. Porcelain or white stoneware can handle a medium cycle up to 2050F. The 125F after that is solely to allow spars to off gas. myth? no... My recommendations are based in proven research. Nerd
  10. glazenerd

    Stoneware Limit Study

    Stoneware Limit Study It has been two years since I began this research project. Perhaps it is time to make my final observations. Stoneware is often referred to as dirty porcelain: some truth to that seeing as all clay is Aluminosilicate. With the exception of titanium: kaolin in general has less than 0.30% of iron and magnesium. Fire clay, ball clay, and other sesquioxides can have percentages of elemental metalloids over 8%. While both kaolin and stoneware clays has various levels of calcium, sodium, potassium ( rare cases lithia ) these add no added benefits other than supplying fluxes. The molar levels of iron, titanium, and magnesium determine the fired whiteness: anything under pure white then becomes " dirty." Above this, the real differences between stoneware and porcelain lies in platelet structure resulting in how kaolin and ball clay holds water. Stoneware originated from basic brick recipes. High iron, large particle native clay were purposely fired to produce carbon coring; which in turn melted the iron in the 1800F ( 1000C ) temperature range. Ball clay was added to produce plasticity, making brick extrusion viable. Grog was added for structural purposes, and to keep oxygen available until the peak. These same brick recipe clays were rearranged to produce the early stoneware recipes. Orton ( the cone guy) heavily researched brick recipes, and subsequent stoneware recipes; with emphasis on remediation of carbon coring. The " slow" cycle on Orton Cone Schedule (108F an hour) came from this research; and specifically designed to overcome coring and bloating. The basic stoneware recipe is: 80% clay(s), 10% silica and 10% feldspar. The only real dividing line in stoneware formulation is: functional or non-functional use. If functional: then absorption should not exceed 2%. The term " vitrification" is now applied universally to both stoneware and porcelain; however stoneware is actually measured by "densification." Densification being defined as the maximum particle distribution (PSD) obtainable to achieve the lowest possible absorption. Vitrification implies high glass content, densification implies maximum particle density. Given the large particles of fire clay, much lower spar levels: zero absorption is unobtainable. Stoneware has a formulation deficiency not found in porcelain: cristobalite formation. Yes porcelain can develop small amounts, stoneware however can develop amounts sufficient enough to render the piece useless. This formulation issue is why all stoneware bodies require a minimum of ten percent feldspar addition. Enough KNaO must be present to incorporate the ejected silica from spinel development into the melt. Excess ejected free silica is the primary cause of cristabolite formation. Stoneware typically has 1/3 less molar flux levels than porcelain: another notable distinction between the two bodies. In the UK during the 1990's, Limoge and Potclay began doing research on alternate flux addition in both porcelain and stoneware. It was found by Potclays that adding 1-2% calcium carbonate helped incorporate free silica into the melt: above these small additions created other chemistry issues. Both bodies produce different levels of mullite, glass, and free silica: although porcelain has little free silica because typical bodies have a minimum of 25% feldspar additions. Free silica in stoneware was problematic because during the spinel phase it was ejected. In addition to calcium, magnesium levels were also increased to counteract this problem. Ougland and Brindley did a qualitative study for the British Ceramic society in the 1950's using X-ray de fraction to measure the amount of glass, free silica, and mullite in a typical recipe: 1200C. Glass 62. Free silica 21. Mullite 19 1300C. Glass 66. Free silica 16. Mullite 21 While additional heat work does add some vitrification properties to a fired piece, it is more reliant upon the molar percentages of flux, and supporting fluxes in general. Typically a cone six firing is the lowest possible peak required to produce functional ware, although some success at cone five is obtainable if flux levels and firing cycles are strictly observed. Regardless, the typical glass to mullite ratio is 3:1. In order for glass to develop: X amount of silica is required: and X amount of alumina is required for mullite to form. The combination of these two variables is where the modern formulation standard of 4:1 SiAl ratio comes from. Again noted this standard relates to functional use. The molecular structure of kaolin and ball clay is the third determinate distinction between porcelain and stoneware. Kaolin is a 1:1 clay particle with no inner platelet: looks very much like a saltine cracker at 25,000X magnification. Ball clay is a 2:1 particle, with some smecite varieties classed as a 2:1:1 particle. Ball clay looks like a sponge magnified: the inner platelet capable of holding a little or a lot of water. Bentonite can hold up to 15X its weight in water. Typical ball clays can hold 1/4th to 2 times it's weight in water. The chemistry is one thing; throwing either on a wheel is another. Kaolin only holds water on its particle surface: which is why it dries so much faster. In addition, this water film acts as a lubricant between particles: making porcelain soft and sensitive to pressure when throwing. Stoneware clays ( except fire clay) absorbs a fair amount of water creating density. Because moisture is absorbed into the platelets: the water film between particles is appreciably less. From this single difference in particle structure: stoneware takes longer to dry and has a much higher mechanical strength when throwing. So my final conclusion: NO, stoneware is not dirty porcelain. There are other unique chemistry distinctions, but I will let them be. Maybe in another two years I will revisit this thread. Nerd
  11. glazenerd

    turq_vase.JPG

    Exploring color I see..a good thing.
  12. glazenerd

    Sodium Silicate variations

    Insight references sodium silicate as 50.78% sodium and 49.22% silica. SG 2.40. Or 280 degrees twaddle. Given all the sources on the web, the potency of sodium silicate is going to vary from region to region. Which in part might explain different results from potter to potter.
  13. glazenerd

    Sodium Silicate variations

    SPG 1.39 x 1000= 1390 - 1000 = 390 divided by 5 = 78 degrees twaddle. Surprised actually. PH 11.3 anything over 11 PH is classified as caustic: in this case caustic soda (sodium) using a torch to accelerate drying is not really a good idea. Like any good acid or caustic alkali: the length of time for reactions to occur will have more effect on outcome. Diluting with 1/4 to 1/3 water to lower the PH to around 10 pr so would minimize the reaction as well. The length of time before stretching the form would also be a factor. sodium is a drying agent: used for centuries to cure pelts, dry meats, etc. In part some of the chemistry going on here.
  14. glazenerd

    Sodium Silicate variations

    The chemistry behind sodium silicate has been somewhat lost in modern pottery. The reaction of sodium silicate at one time was measured in " degrees twaddle." I think some places in the UK still use this measurement of potency. Once upon time, sodium silicate was sold in 75 or 150 degrees twaddle. The lower degree being used for minimum thinning of slip, or often used in colloidal chemistry. 150 degree twaddle was obviously twice the potency as 75 degree twaddle. So it was used to thin heavy slips, or in half proportions. Sodium silicate has a more important role in slip besides "thinning." ..more chemistry for another day. that said: I have tried for several years to pin down the potency of sodium silicate sold in the USA- with zero result. However, from testing and results: most likely 150 degree twaddle. So experiment: dilute it by 1/3, 1/2, and 2/3rds with water and see which result you like. You can also use aloe (sold by the gallon for $15) organic, burns off. T
  15. Jason: i own an SS 20 and have used Shimpo before. Regardless of the maker, each will have its own issues when straight water is poured into the chamber. If I pour water into the back of my pugger, in tends to leak into the vacuum chamber. Puggers work in part by creating pressure on the chamber walls: which include the hopper lid. TIP I mix all of my own clays from custom blended recipes. I blend 50lbs dry, setting aside the plasticizer. In the case of stoneware, that plasticizer would be the plastic ball clay. I mix the plasticizer with my pre- measured water the night before to hydrate it. Before I mix, I add the dry powder mix to the water until it becomes a thick slip in consistency. After I load the chamber with dry powder, I pour in 1/4th the slip water and run it for a minute; open and add another 1/4th, mix for a minute..repeat until most of the slip water is added. I keep back about a quarts worth. Then I mix for five minutes on med. high/ check consistency: then add either powder or slip water accordingly. Blends much better than straight water because the slip water has body. T
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