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Everything posted by glazenerd

  1. saggarflowbluandpeachcopy.jpg

    Most interesting. I see a bit of translucence, a bit of bone china, and the effects of Parian. Think you have dialed into a technique that works. I can certainly see market appeal.
  2. Confusing Glaze Result

    Joseph: The recent complaints I have seen about clay being too wet, or not acting or firing like before; is not really manufacturer related. Like the big Custer change back in 1999; some of the raw clay mines are older; and are digging into new areas. Some of the old tried and true ball clays have enough compositional changes, that in turn effect water retention, color, etc. I would suspect clay makers are working through the changes; some will require a fair amount of time to resolve. i would recommend you stay away from any porcelain labeled as " translucent." Given the glazes you are using and the application rates: they would cause you some aggravating pin hole issues. Remember, higher translucency = higher flux levels! which = higher off gassing of spars, which = higher incidence of pin holes. Just as you are finding out that dark and red stoneware bodies can have variations in natural iron and magnesium levels; which effect glaze color. So again, raw clay materials are changing as they dig through the strata. There is an old tried and true ball clay that has been used in Terra Sig for years. I recently received an updated analysis showing higher carbon, sulfur; and larger particle size distributions. I tested the WOPL index last year: it now holds ten percent more water than it did five years ago. It is widely used in stoneware as well, which would translate to "wet" clay. It also means Terra Sig will not settle out like before, and the SG will be different. the higher CEC and WOPL changes the physical properties of the end product. * notice I intentionally left out producers and product names. Tom
  3. Confusing Glaze Result

    Joseph: These are all stoneware bodies with various levels of iron in each. All are cone six, all with clear glaze: so the color is coming from the clay blends only. Obviously, the dark brown on the lower right has the highest content, and the blush color the lowest. The deeper blush has iron, with natural magnesium. The yellow/ straw is the middle of the road iron levels. I have a grey floating around somewhere. So yes, the possibility of lower iron in the raw clay is a possibility. I think LT's suggestion will help narrow down the cause.
  4. To obtain translucency; two primary changes in clay chemistry has to occur. The first being high purity grades of kaolin are required.The second, at cone six flux levels have to increase by 15-20%. Giving the conditions you are describing; I will go with 15-20% increase of nepheline syenite. Why? Because sodium in an aqueous solution will cause a hydrophobic reaction: meaning it has the tendency to repel water. In your case: rapid drying = cracking. Pending the sodium level, there may be a slight exothermic reaction as well. Anyone who has poured a plaster mold has felt this exothermic reaction when as it sets up: the mold gets warm. Wait 30-60 minutes after you pour: is the mold slightly warmer? If so, simple proof of high sodium content. If this holds to be true: then you need to pull the form much earlier. Only experimenting with the time will tell you when. High levels of sodium also means higher PH levels. The higher the PH, the faster it will dry. Higher PH will also effect plasticity, which will also cause cracking. You can try this simple (possible) fix: add 3 drops of vinegar to one cup of slip: stir then pour. Check the form for improvements. If cracks are less, but still present: add 5 drops of vinegar.in essence, you are Titrating the PH level back into the 8.35 range; where porcelains should be. Lastly, if Nep Sy is the flux of choice (usually is because it is the cheapest flux available) then you will have other issues arise in the near future. Nep Sy has 14-20% soluble salts that will build up on your molds in a short time. This build up will degrade your mold much faster than the norm. if you have other suppliers available to you, mark's advice of finding a new slip is a good idea. All depends on how much time you want to spend dialing this new slip in.
  5. IMG_1612.JPG

    I have a crystalline recipe that uses cobalt and tin; plus a dash of rare earth oxide. The end result is similar to yours.
  6. saggartilesTurnercopy.jpg

    The pastel(s) are unique and appealing. The bone white of the porcelain certainly adds to the effects. Sometimes experimenting pays off.
  7. IMG_1612.JPG

    Obviously cobalt, but adding tin perhaps?
  8. saggartilesTurnercopy.jpg

    Nice color development. On porcelain I assume?
  9. 5a99f54ebebd7_floridaleafpotsbowls006.JPG

    Very nice piece AH, well done.
  10. Owls

  11. PQotW: Week 41

    1-3 the rest, no idea. Although I have been reading posts on kiln building. ( reason I knew #1 )
  12. 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
  13. 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
  14. 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
  15. 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...
  16. Iron migration

    From the album USB Images

    Stoneware sample with 30% Hawthrone blend. At 2050F, the smaller particles are melting and beginning to migrate.

    © TJA 2-18-18

  17. USB Images

    Taken with 20x to 800S usb microscope
  18. 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.
  19. 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
  20. 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.
  21. 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.
  22. 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
  23. Raku Rocket - Kiln #3 by Ian Gregory

  24. Wish I could hit the like button on this comment ten more times. the first two years I fired crystalline glaze; 98% hit the trash can! road fill! and on really frustrating days- UFO's. i do not consider myself a potter, I do not have the skill level to paint those pretty details, form a perfect handle, and can barely make a straight cylinder. I just do not have those skill sets; BUT I will learn over a period of time. I can make porcelain or stoneware bodies react or act the way I want, or any color I so choose. I can also make cone 5 crystalline look like it was fired to cone ten. So I do have pottery related skill sets. As John Baymore often reminded me; I do research primarily. I seem to enjoy that more than making pottery. i think Charles Dickens might have been a potter on a side: "Great Expectations." Tom

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