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About glazenerd

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    Clay chemist

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  • Location
    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. 5a99f54ebebd7_floridaleafpotsbowls006.JPG

    Very nice piece AH, well done.
  2. Owls

  3. PQotW: Week 41

    1-3 the rest, no idea. Although I have been reading posts on kiln building. ( reason I knew #1 )
  4. Why not underfire clay

    Cone 5-10 bodies are primarily fluxed with potassium/ sodium spars; which at cone 04 only fuse materials together. These body types are actually expanding, becoming more porous until they hit 2050F, when they begin the early process of vitrification. These body types have absorption rates in the double digits if only fired to 04-06. So they will fail over a period of time if used for functional purposes. Plenty of threads on fired pieces absorbing water causing mold, foul tastes, and odors. Low fire bodies use different fluxes; such as talc ( magnesium) or boron. These have lower melt temps and do increase density, although still not for functional use. The more applicable effect is changing the COE of the clay to be more in line with low fire glazes. Nerd
  5. I decided to make a " late in life" career change. After 42 years of building houses, developing subdivisions: and teen years plowing, planting, and milking cows: thought it was time. My new profession included being a couch tater, laziness, and idleness in general. So far my new profession has not panned out; people keep calling me to build stuff. Nerd
  6. There is a word used to describe clay properties, from the 40-80's: but since forgotten. "extensibility" was used to describe how far a clay body would extend without rupturing or collapsing. It is the physical properties of fireclay and ball clay, as compared to kaolin that give stoneware or porcelain their throwing properties. You can formulate porcelain to be firmer, or stoneware softer. now back to my coffee, I feel an information dump coming on. nerd
  7. Doc: picture is worth a thousand words. The iron is migrating / melting at 2050F, as the temp climbs the other large particles of iron will join in. The GPA inside the clay body will push it towards the surface. I called Van der Walls, his wife said he is resting...
  8. USB Images

    Taken with 20x to 800S usb microscope
  9. Stoneware: Buff to light tan. 0.75 to 1.25% iron ) very common to have up to 20% kaolin. ( no iron) deep tan to light brown. 1.50 to 2.25% iron dark brown / slight reddish 2.25 up 3.00 iron. However, at this point carbons are also increasing, and bloating issues possible. red stoneware.. 3.00 iron and up. All red clays are high iron- 5-7% by weight. The darker the clay; the higher the iron AND higher the carbon content. Most all iron in clay comes from iron sulfide FeS. It is the off gassing sulfu (ides) that cause bloating, not carbons. doc.. Never ask a nerd for simple answers.
  10. Buying clay for first time

    http://www.lagunaclay.com/clays/western/em217.php the recipe originated from the old Walt Disney studios. (WED) his initials. Non- firing, meant to be used for the purpose you presented. Nerd
  11. Because a thin layer of porcelain can still leach the iron, magnesium, and titanium from the stoneware body. The higher the metal oxide content of the stoneware, the greater the degree of change in the glaze. Then comes the change in refractive index. Etc.etc. blah blah and blah.( short version of lengthy chemical reactions) Nerd quick clay chemistry lesson: translucent porcelain has less than 0.25% molar iron, magnesium. And less than 0.50% titanium. regular porcelain has less than 0.50% iron and magnesium! and less than 1.00% titanium. As the flux content goes up, so does the translucency- via glass content. stoneware can have anywhere from ..75 to 7% iron! higher magnesium! and titanium. as all glaze makers know??iron and magnesium are colorant oxides. As the content goes up in the clay, it leaches into the glaze and changes it's color. Does the same thing to porcelain slip if too thin, and if the stoneware has high oxides content.
  12. Peter Pugger VPM 20SS

    I bought a VPM 20 last summer. As with all things new, there is a learning curve. As a pugger, it works just fine. As a mixer, it will take some time to learn the tricks. The first trick is not dumping in all the water at once; you will create a rather nasty slime ball that just spins in the chamber.
  13. TY CPD... Congrats on a very niece piece. You have an appreciable talent. 1. Due to the weight (75lbs. +|_) dry, you will have to fire this on a bed of course sand. Some would suggest wadding, but I think this piece is too heavy for that method. Clay will shrink 10-14% when you fire it! which means the base that makes contact with the kiln bottom will shrink that much as well. So you MUST plan for that movement, and allow it to move without drag; otherwise you will crack it. 2. Absolutely fire on slow speed (108 F) an hour climb. This piece is 1.5" thick, so it will take time for heat to penetrate that thickness. I have read studies from various Universities using lab equipment to measure the effect of heat on clay. For instance; if the surface of the clay is 1000F, it could be an additional 30 minutes before the core reaches that temperature. One of the reasons extended holds are often used to cure pinholes and give clay the time to finish off gassing. 3. Quartz Inversion. This will be the problem child for this piece due to its weight , size and thickness.quartz Inversion is when the silica in the clay (quartz) converts from the alpha to beta stage at 1065 F or so. I think for those across the pond it would be 563C. The simplified explanation of this reaction would be: a molecular earthquake. All the clay particles start vibrating ( reaction to heat) to the point it can literally split the piece. Many threads on the topic. Personally, I would program a 50F an hour climb from 1000 to 1150F to make sure the heat equalizes in the core. You cannot push this piece too fast through this critical temperature range. 4. This piece will require an extended hold at peak firing temperature in order for the heat to reach the core. At minimum I would suggest 30 minutes. Personally, I would candle it for a few hours just to make sure it was driy to the core before starting the temp climb. Others might find that excessive, but I see it as a few hours of added insurance. Too nice of a piece to take chances. i have a 15.5CF kiln: the maximum piece would be 24 x 24 x 34 tall. You need to locate a kiln in the 20CF range to fit this piece in. Nerd
  14. Raku Rocket - Kiln #3 by Ian Gregory


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