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Everything posted by glazenerd

  1. Your clay is fine; just need to wedge it throughly. T
  2. Min: sorry it happened to you, never fun.
  3. Had a long discussion with the math professor from SIU-E about writing math equations for crystalline glaze: she thought it was doable. Interesting!

    1. Show previous comments  3 more
    2. Benzine


      You do eat it, but only a little over three pieces...

    3. glazenerd


      Are these three pieces squared?

    4. Benzine
  4. I will post pics, but it will be late summer probably. Mark called it a 50/50 shot, I am going to attempt crystalline glaze, so that is probably a fair estimate of success. T
  5. Sophia: if you cut up a 4" tile setter and use them as open racks; you can candle and bisq easily. You can also glaze fire, but extra care must be taken to ensure glaze is not making contact. It allows full circulation of air/heat. Tom
  6. After bumping into a painting contractor friend: now I am going to sand blast off the old glaze. (50 grit carbide)
  7. Mark: The auto sanitizer model: when you flush the kiln door closes and fires to 1000F automatically.
  8. Melanie: this article in CM will give you the basics on clay bodies. Direct link: https://ceramicartsnetwork.org/ceramics-monthly/ceramic-supplies/ceramic-raw-materials/techno-file-clay-body-shopping/
  9. B-mix (white stoneware) has 10-25% kaolin content- hence the "white." B-mix usually blends 50-60 mesh fire clay in lower %, which still allows for some body but without feeling any tooth when throwing. In addition, higher % of fine particle ball clay, with higher % flux= lower absorption values. But that also means higher COE values. (stoneware only application) you can use absorption data to help pinpoint COE values if none are given. To lower absorption: the body requires less large particle, more fine particle, with higher flux% in order to lower absorption: which means higher COE. conversely larger particle with less flux = higher absorption! with lower COE. ( generalization). Tom
  10. Spiffy: porcelain will always have a different feel than stoneware due to structure of kaolin clay. premium porcelain typically use premium plasticizers: macaloid or gums. Premium porcelain bodies have purer kaolin grades, premium plasticizers, and higher flux levels in order to achieve higher degrees of translucency. They typically have higher COE values for those reasons: Frost for example is 6.99 COE. Frost uses a gum ( not v gum) that creates that tacky feeling. Premium porcelain are off white to light buff in color. standard porcelain uses ball clay as a plasticizer: they can be tan to light grey in color. They fire to a high white, but little to no translucency. They are more user friendly starting out. COE bounce from 5.25 to 5.75 pending the amount of ball clay and flux. Buy according to cone rating. EX. Fire cone 6 to 6. Do not fire Cone 10 to cone 6. Porcelain is dependent upon flux levels to produce the glassy matrix that results in nearly zero absorption if fired correctly. Tom
  11. Tom: it is already broken down- just sat it in there to check space.
  12. Hi Moon- welcome to the forum. some pottery supply houses sell "china sand" which will work. Plain river sand will also work. River sand is also used by brick layers, also used in pool filters. If the edge is wide enough to support the weight, then yes. the other issue is quartz inversion which occurs at 1064F (563C) when firing large pieces, heavy pieces, or pieces with a lot of shelf contact: slow the firing down to 100F an hour from 1000 to 1100F. Do a forum search as "quartz inversion", I recall that thread from a few years back. Tom
  13. Leopold: large particle mesh does not suspend/disperse well in slip: so throwing would be a better option. If you are applying this slip over a clay body; while constantly stirring to keep them momentarily suspended, that would be possible. Mica changes from different deposits: so I cannot say with certainty that higher mesh size 50-80 would help, but theoretically I would think it would help. Mica is usually opaque, so I am curious about the source material. If the black color comes from iron, manganese: you will get your desired color. If it black from carbon, it will burn off at higher temps. I would have to assume this perticular mica source has been used for speckles before. Tom
  14. 1. Water content of the clay..the obvious variable. 2. % of ball clay or other plasticizers. These hold water longer than kaolin, dry slower. 3. Sodium vs othe fluxes: sodium accelerates drying..hydrophobic material.
  15. Low fire bodies typically run between 7-9.50COE, unless talc has been added to lower that number. Vitrification does not begin until 2050F. A cone 6-10 porcelain body fired lower would have a COE of 10 or above: the higher the silica %, the higher the expansion when under fired. correct, the COE of pit fire would be high regardless of body formulation. Again, the higher the silica%, the higher the expansion. The reason pyrophyllte is used in raku, or other "thermal shock" bodies; much more tolerant of rapid changes in heat. silica starts expanding at 1064F, (563C)
  16. Neil: got the porosity issue , did not know if there was a preferred COE.. Apparently not.
  17. Neil: if flame and oven ware are done in the 4-4.50COE range- what range do you think would work? T
  18. Bill: I have a ten page article on sanitary ware I am trying to find. Read it about 5-6 years ago: although the article was mainly based in the reduction of failures on the assembly line. They did get into firing temps however: as I recall it was around cone 1-2....But it has been too long. Next time I get up to the warehouse, going to cut up a few tank lids and take them on a test drive. Denice: back in the 40-60's, absorption test were done in autoclaves with 100 psi of 350F steam injected. There are numerous journals from those days on atmospheric moisture causing delayed crazing. They autoclaved glazed pieces as well, in an effort to pinpoint that problem. Tom
  19. LB: think we are surrounded by nay- Sayers!!!! Now I will have to fire one this summer.
  20. Leopold i can offer you an educated guess. Mica forms in sheet layers. ( schist) 20 mesh is large enough to have many; the heat caused expansion in those layers: and the outer layers popped off. I assume you already know most mica has 13% potassium, so I will venture to say you were hoping they would bleed? Tom
  21. It's official: you are now a veteran potter.
  22. Erin: your piece from class is on a high iron stoneware body. Copper reacts to iron, color shifts. The glaze run also indicates higher cone fire. Your new piece is on white stoneware or porcelain ( low-no iron), so that alone will change color. The glaze does not strike me as being mature: need more heat. I know DH fires a lot of SCM, so I would follow his firing schedule. Your pinholes are from potassium by the way: sodium creates much smaller pinholes. Tom note: EPK would be the better kaolin: much finer grain than #6- better melt.
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