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Everything posted by glazenerd

  1. Many stoneware recipes have switched to Nep Sy as the primary body flux (Cone5/6). Nep Sy in the USA can have up to 14% soluble salts that migrate to form hard nodules in clay. You are getting the larger bits, many more smaller. No practical way to remix to consistent distribution. Tom
  2. Low fire bodies (06-04) incorporate talc primarily as both a flux (magnesium) and to control thermal expansion. Low fire bodies without talc can have COE values above 12, and bodies with talc can have COE around 9-10. Boron is also used in low fire bodies as a flux: both magnesium (talc) and boron are lower temp melts. Cone 6 bodies use KnaO (sodium/potassium) as the primary body fluxes that begin to melt around 2050F. In addition, cone 6 stoneware bodies have COE between 5-6 typically. While you can certainly mix the two and fire low: any functional use properties will be lost. Secondly,, you
  3. Shelley: I fire macro-crystalline glaze: but have no experience with commercial premix. Do you have links I can read on these products? Will take a look and see what's applicable. Tom
  4. Peter: In the numerous studies done on the effects of heat work- one in perticular is applicable to your question. It found that it can take up to 30 minutes for the ambient kiln temperature to penetrate a 1/2" clay wall. In your question: ambient temperature has to penetrate a 2" clay wall: which means there is always going to be a lag between the exterior and interior wall temperatures. As Mark noted: 10-12 hours of candling is well within reason to ensure moisture is driven off. Personally, I would not climb more than 108F an hour during the whole process. White stoneware has 15-25% k
  5. Anna: given the current blister population (few) you are close to resolution. You had one clear, two pieces blister- very close. Inorganics in dark/red body clays burn out from 1250-1750F. Program a firing segment at 108F climb between these temperatures; or just select slow bisq cycle. (Most are 108F an hour climb). If the kiln is heavily packed; open a peep hole to supply oxygen- also important. Tom
  6. I see a dark or red bodied clay from the pictures. Every potter has their definition of pinhole; but I would put those in the blister category. I can see bare clay in the center, with raised rims; both signs of gasses escaping under pressure. I suspect these were fired at a medium,or fast speed during bisq from .1250 up to 1750F. Which leads me to believe this is off gassing from iron disulfide, that will produce this type of blistering.
  7. The sink rail is 25" x 3/4" after bisq firing. Could only find a half slab left from that job. Note: failure rate on this job was almost 15%- not uncommon for big slab work.
  8. Bone China is mostly a commercial body these days: formulated as a soft paste or for jiggering/press. Some potters mix their own for specific use. FINd: Grolleg porcelain with shrinkage 13.5% or above, with preferable BentoneMA plasticizer. That formula will allow you working time, will accept stamping or detailing well. Edit add: and will fire high/bright white which will not interfere with color. T
  9. The largest solid porcelain slabs I have fired were 65cm x 2.5cm thick: custom countertop slabs. There are several tricks and protocols you will have to follow starting with your clay. Plasticity level has to be much lower than typical porcelain used for throwing. High plasticity= high shrinkage= higher memory. You will have to customize tile setters to his fire them on edge to avoid drag. You will have to candle them even if you are sure they are bone dry. The cheek test does not work on thick slabs. Finally, you have to customize the firing cycle. T
  10. Babs: Threw 6% yellow into a white stoneware (left) and porcelain (right). Even low levels of iron in white stoneware causes major color shifts- mostly headed to the brown/tan area. The stoneware (left) is half glazed, half raw @ C6.
  11. glazenerd

    Clay Tests

    Testing includes flux variations, modifiers, and clay blending.
  12. From the album: Clay Tests

    Cone 6 Terra Cotta Unglazed. Body developed from locally sourced (wild) clay with hematite iron source.

    © TJA2020

  13. Organics: most likely Ord or Muck variety humus. Both carry very high CEC values (plasticity), as both absorb and hold moisture. Not uncommon for these materials to take several days longer to dry compared to commercial clay. You cab burn off Organics by heating up to 1150F. Organics may be the only plastic material in your wild clay: burning them off might have adverse effects. Testing is the only way to know. There is a Facebook group- "Wild Clay Club" devoted exclusively to processing/firing locally sourced clays. Not many threads about it on this site. Tom
  14. Babs: Been running "reaction" tests since last spring on colored porcelains. If the kaolin has higher titanium; there will be A color shirt; but those are fairly subtle. Iron bearing stains react excessively to zinc lazes. Zirconium based stains are the most stable. % of stain matters; but brown/gray result is typically a reaction. "Ody" stains are the most reliable and predictable. When I get a chance, I will snap a picture of some reactions in yellow, purple, and brown. Not been overly active lately- many posts get past me. T
  15. Have my concerns this clay body has formulation/contamination issues. The recent two samples are fired to?
  16. glazenerd


    Always liked this pattern.
  17. glazenerd


    Nice work Johnny.
  18. Very nice pieces. Burnished?
  19. Very nice forms/effects-well done!
  20. Depends if the grog is being used to increase structural support: sculptural for instance. If used for appearance; then the parameters change. Mullite and molochite are commonly used in red or dark body for "speckling; or manganese/iron in white body or porcelain. The human eyes can see 50 mesh; so 20-50 mesh is used. 1% of 60 mesh manganese for example will produce 400 "speckles" per square inch. Stoneware bodies will handle 0.25 to 1.00% additions with nominal effects on absorption. If your clay body produces a consistent cream when you throw; there should be plenty of fines to encapsulate g
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