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glazenerd

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About glazenerd

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    Now & Then

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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.
    Feb. 2019 Ceramics Monthly- Clay Body Shopping Guide
    March 2019 Ceramics Monthly - Porcelain 201
    June 2019 Ceramics Monthly Clay Restoration
    Sept. 2019 Clay Memory
    Oct. 2019 Firing Programs

    Email: optix52@aol.com

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  1. Hey dank: Iron based stains work poorly as body stains. "Seal Brown" is similarly based iron brown stain that mixes dark, but fires very light with a heavy taupe cast. "Woodland" is more expensive but requires far less stain:1-2% for lighter brown/ deep tan. The bottom right hand corner is Woodland. At just 5% it fires a deep brown. Of equal importance is the clear glaze you select. Any glaze containing zinc will produce a matte/ microcrystalline finish. Boron based clears produce a clear/Hugh gloss finish that illustrate colors well. Matte clears will change color as well.
  2. Chloe: been thinking about your unique goal. You will need 1lb of OM4 ball clay (or equal), 1/4 lb of silica, and 1/4 lb Nep Sy, Custer, minspar, mahavir or flux readily available to you. Mix it at 80% OM4, and 10% silica and flux. If you do not have a scale then: 1 cup OM4 ball clay, and 1/8 cup each of silica and flux. Mix it throughly dry and place it in a bowl by your wheel. (Keep a tablespoon in it.) After you finish throwing; with clay cream still on your hands: spoon one tablespoon on one hand and rub your hands until coated with the mix. Now go back and let the piece run in your hands; allowing it to pick up the dry mix. Then collapse the piece and cone the lump several times to throughly mix it in. Remove and wrap in plastic. This lump can be reused in 5-7 days. Remove, wedge, place on wheel; cone a few times- off to the races. Enjoy! Modified to fit your protocol. Exact chemistry? No.. but close enough for your needs. Nerd
  3. I have a Paragon 1613-3 express which fires well. Plenty of power/3" walls. Also had a Caledra which I abused in test firings- still had 1200 plus firings. Saved the controller and wiring; going to rebuild a custom test kiln with 4.5" brick.
  4. Retha: Welcome to the forums. If you are starting from dry powder premis: do one 500 gram test batch with 50 grams of ball clay (10%), and a second 500 gram test batch with 75 grams (15%) ball clay. If you have moist clay; then calculate dry weight by subtracting 20% for water. 1000 grams moist minus 20% water (200 grams) = 800 grams dry weight x 10% ball clay = 80 grams added to moist clay. Ball clay comes in low, medium, and high plasticity; so your experience with local materials will have to guide you. White stoneware has low iron and magnesium; which will also guide your ball clay selection. When hand mixing or slaking premix clay; it will take 5-7 days for plasticity to develop; 3 days if using a deairing pugger. Bentonite can be used as a plasticizer; more commonly used in porcelain. 3-5% addition would be a good starting point. Important that you throughly blend in bentonite before adding water. Bentonite does not take kindly to being wedged into moist clay; I would avoid it. 500 gram test batches are more than adequate to test plasticity. Do not overdo ball clay additions because they do absorb water; excess can cause slumping or folding when thrown- in addition to higher shrinkage rates if handbuilding or doing slabs. Nerd
  5. More info in the link below. On the first page-4th post zinc additions are discussed. There is a pic that shows 24-25-26% zinc additions.
  6. IN the middle of 100 glaze crystalline tests. No problem with shades of green, shades of blue. Looking for tips on two things. 

    #1 Oxidized red ground or crystals without the use of cadmium ( toxicity)

    #2 Yellows 

    #3 Creation of distinction of ground colors and crystal colors 

     

    1. glazenerd

      glazenerd

      Answered on your thread in Clay/Glaze zChemistry

    2. Mark C.

      Mark C.

      100 tests-now thats a bit of time

  7. Commercial iron bearing clays run 5 to 8.4% iron content; less after being blended. Your experiment illustrates what causes carbon coring. Starve the oxygen during burnout and sulfur dioxide gas reduces the iron and causes carbon coring (black coring.) Supply plenty of oxygen during burn out phase; and it off gases as carbon trioxide with no adverse effects. The large opaque, clear, or silver crystals found in granite is crystalline silica. In the States; certain granite is ground to make silica.
  8. Being from the West coast and given the price of the clay and results. Most likely IMCO Burgundy clay which fires dark brown at cone 5. Add 3% +/- black stain and you have black stoneware. I would recommend bisq firing on slow ramp to 1800F (cone 06) If it is indeed what I suspect: IMCO is an iron disulfide clay with a fair amount of inorganic purifies. A slow bisq will burn off the impurities; which in turn should minimize the pinhole issues. Avoid any glaze with zinc added: zinc reacts strongly to iron disulfide. If you have a picture of the bottom unglazed area of your piece: it would with identifying the clay. (Problem) Colored porcelain (black) fires ultra clear.
  9. Liam: not addressed, but a good point. Several other universal kiln principles still apply.. A dense bisq load as you pointed out would benefit from a pulled bunge. Red body clay is often used for very large platters and yard planters. Potter posted a pic of a 56lb bowl awhile back; with 3/4" walls. A case were sand should be under the foot for movement; and the ramp rate slowed to 80F an hour or so. An extended hold at 1800F would also be advisable. Several studies show it takes ambient kiln temperature up to 30 minutes to penetrate a 1/2" clay wall. Tom
  10. Color development can also be achieved by changing your firing speed. Most controllers have slow, medium, and fast preset firing speeds. By simply changing from fast to medium firing speeds; additional color development can be achieved. Red bodies containing iron disulfide should be fired as recommended to bisq temperatures 1800F/ 1000C. Glaze firing can then be adjusted to fast or medium for color development in the glaze fire.
  11. Firing Red Bodies with iron disulfide. Red bodies that source iron disulfide, and or red bodies that have inorganic sulfides require changes in the firing cycle to prevent blistering, bloating, and carbon coring. (Also called black coring) Hematite and magnetite have oxygen binders that creates the crystal lattice. Iron for example is FeO Fe= iron. O = oxygen. Firing clay bodies that source these two iron varieties, cause few issues. Most red clay bodies in the USA and other places source iron as iron disulfide. (FeS) Fe= iron S= sulfur/ide. When firing red body iron disulfide special attention to the firing schedule is critical. Disulfide is an inorganic binder that off gases between 1250F (655C) to 1750F (955C). For this singular reason all red bodies needs to be bisq fired to 1800F (1000C) minimum. Edward Orton (the cone guy) did the early research work on iron bearing clays from 1904 to early 1920's. He wrote numerous ACER journals on the kiln firing techniques required to properly fire and burn off the sulfides in red clay bodies. The slow ramp cycle on Orton controllers is based on his research. In lieu of the slow bisq ramp: a programmed ramp from 1250F to 1750F at 108F an hour climb is required to successfully burn out the sulfide content. Pending the size of your piece (over 10 lbs. or over 3/8" walls) you may need to slow down to 80F an hour between 1250F to 1750F. If you single fire red bodied clays: simply choose slow glaze fire or program a firing segment from 1250F (655C) to 1750F (955C) at 108F an hour climb.
  12. If red body clays that source iron disulfide are improperly fired; the off gassing inorganic gases can create color shifts so dramatic it renders the glaze useless. Porcelain control tile on left: iron disulfide samples in middle and on the right.
  13. An additional test was performed to check the reaction of the three iron sources to other metalloids. Copper carbonate was added to a zinc free clear glaze, then a zinc free clear glaze: then finally 3% zinc was added to the clear base glaze. Copper carbonate had strong reactions to all iron varieties in comparison to the porcelain control tile. Zinc free clear glaze performed well, with the exception of the magnetite (M) sample. When zinc was added at. 3%: there was a color shift on all samples; with crystallization occurring on the IM sample. Magnetite had the strongest reaction to zinc with a wide color shift and blistering occur. Ledger: IM- IMCO Burgundy. N- Newman Red H- hematite RA- Red Art M-magnetite. When using clear glazes on red bodied clay bodies; there are often complaints about matting. In this close up (3rd pic) of a zinc free (left) and zinc added (right) crystallization of the iron has occurred; which is often mistaken for matting. Iron crystals refract light differently, giving the appearance of matting. Where the clay and glaze meet is commonly known as the clay- glaze interface: enough of the iron has been pulled out of the clay body into the glaze to cause iron crystals to form. In addition: red clay bodies that incorporate iron disulfide as the iron source can cause matting if improperly fired. Close up of zinc free and zinc added clear glazes and the reaction to iron varities.
  14. Any red body clay sources iron to obtain its primary wet color. Iron disulfide with additional sulfides from lignite coal particles can have dramatic effects on colored glazes. The picture below shows yellow, red, green, and turquoise stains mixed with a zinc free clear glaze. The Mason Stain color number is noted on the sides. The pure porcelain tile to the left illustrates the dramatic color shift iron causes. The magnetite and Red Art samples cause enough reaction to render stains unusable. Porcelain on far left was used as a color control reference. Ledger: IM- IMCO Burgundy. N- Newman Red H- hematite RA- Red Art M-magnetite.
  15. The starting point for red bodied clays is the color when moist. The most commonly used clays in North America are IMCO Burgundy, Newman Red, and Red Art, in addition magnetite, and hematite are locally sourced and or used in other countries. Iron bearing clays can also be grey (Canada), or have a distinct green hue ( Southern USA). Green hue typically indicates that higher levels of calcium and magnesium are present. Grey can be higher magnesium; but most often the color comes from sulfide contaminants (lignite coal particles). Red Art also has a high sulfide content which darkens the red hue. Clays with high sulfide content require different firing schedules than hematite or magnetite bearing clays. Notice IM and RA have reddish brown and reddish/ grey color when wet: both discoloration indicate clay impurities that include lignite coal particles. Ledger: IM- IMCO Burgundy. N- Newman Red H- hematite RA- Red Art M-magnetite.
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