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douglas

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Everything posted by douglas

  1. Just curious, how could they know what glaze they wanted, when they have not seen what it looks like on the stoneware clay? Assuming they picked a test tile, why not use the same clay used on the test tile? It is unlikely to look the same on a stoneware body.
  2. I use a cone six red clay and it comes right off. However when I use it in cone 10 that sometimes happens. I think your clay may be over firing if the alumina gets embedded in the clay. I still use it in cone 10 but I know I will have more clean up and finishing later when I do.
  3. Pour the slip in with your saved trimmings and slop and reclaim the clay.
  4. I second the plaster wetbox advice if you have the space to store the pieces. Mist them and forget them for a few days, and concentrate on making new pots. Pull some handles and store them with the cups. They will stay perfect consistency until you are ready to connect them, and the handles will match the moisture content of the cups. Getting the right amount of water in the plaster may take some fiddling at first, if things are staying too dry pour more water onto the plaster in small amounts.
  5. You don't want to go that slow, since it can lead to drips and runs. Instead do a smooth line, and then go over the same spot once the surface dries. 2-3 coats should be thick enough for most colors. Black or dark colors may only need one coat.
  6. I was going to say the same thing -- get a degree from your current college and start researching MFA programs. Most undergrad programs assume no prior knowledge of clay working, and probably won't challenge you enough.
  7. If you have a pottery supplier that rents kiln space, or a community studio, or a community college you can take classes at, you can get access to a kiln. Buy bisque tiles, by commercial glazes, and paint your designs using glaze. When they are fired the colors will be formed in a glass coating and will resist the elements for years.
  8. Most waxes ignite around 200-250F. Using a heat gun might work better than a hair dryer.
  9. My bet is that you are putting the tiles on hot brick, and the thermal shock is what is cracking them during firing. Try using cold brick to rest the tile on and see if that helps.
  10. One other possible cause is too much glaze or using a runny glaze on the inside of the pot. Maybe when you are pouring the glaze out it is taking a while and the inside has a thicker than normal application? If the glaze is too thick at the bottom of the pot, and if the glaze doesn't shrink at the same rate as your clay body during firing, the thick glaze pooled at the foot is creating a stress crack and the sudden temperature change is causing it to fracture along the spot where the thick glaze ends and the clay wall begins.
  11. Plastic bats seem to cause more cracking than plaster or masonite bats. If I have to use plastic, I wire it off immediately after throwing, and flip it onto it's rim when the rim is strong enough to support itself. If the base is too soft to flip and will sag, then I transfer the plate to a board with newspaper so the base can move easier as it dries and contracts. With plaster or masonite bats, I think they wick away enough moisture from the bottom of the plate to avoid the stress from uneven drying on the rim and the foot, and I don't have to be as careful.
  12. If nothing comes out when you flip the mold over, then you might not be filling the mold up completely. If the walls are hollow that would explain why you are getting two halves instead of a solid bowl. You need to screen or thoroughly mix the slip to remove the lumps. You may also need more water in your slip if it is not able to run all the way into the mold before it dries at the base, blocking you from adding enough slip to fill the mold.
  13. If you have access to a ball mill, try running the glaze through that before using - that might break up the particle clumps.
  14. Glaze fit means the glaze shrinks at a rate close enough to the clay body shrinkage, that it will not crack or shiver off the clay. Just because your glaze and clay are firing to the same cone, does not mean the glaze will fit the clay. Apologies if you know this, but it seemed like you are equating firing temperatures with whether the glaze should fit in your descriptions. The root of the problem you are experiencing is you are buying off-the-shelf products. Since you don't control the ingredients you don't have control over whether they play well together in the kiln. Learning glaze chem
  15. Coleman porcelain has warped quite a bit in wood fires for me (cone 10-12 with lots of ash). You might want to load fewer porcelain pieces since your space is limited.
  16. Some general advice is to do a good amount of research before diving in with any ceramic project. The lusters you want to use are toxic to work with. If you use precautions it is not a problem, but if you don't it can lead to health problems. I don't know if luster glazes are safe after firing with prolonged skin contact. It's worth checking out before you make these. Lusters are not glazes. They are metal and binders that melt and adhere to glaze and I am guessing they would not hold up to daily wear and tear on jewelry. If this is just for you and friends that may not be a big deal, but i
  17. My guess is you are letting them dry on plastic or some other smooth surface. The rim might have adhered to the surface (lots of moisture trapped under plastic could make a small amount of slip where the rim touched the surface). When the foot and insides of the platter shrank, the rim stayed put and caused the cracking. One fix for this is to use paper or foam under the pot while it dries so the clay can easily move on the surface as it shrinks.
  18. Use a cheese cutter wire with adjustable roller. Hold your thumb on the roller while you cut or glue it so that it won't roll. Hold the wire against the rim of the pot, and adjust the depth of the wire to the roller to 1/3 or 1/2 the width of the clay wall. Then when you cut the roller will prevent your from cutting too deep (assuming consistent clay wall thickness).
  19. It might be possible to dip the thin delicate bisque in an engobe to build up the clay thickness and re-bisque the piece.
  20. Sounds like your supplier may have sent you a bad mix of glazes. It sounds like they send you a premixed bag, so I would contact them and see if any of their materials may have changed. It does not sound like a user error on your part, but a problem with the glaze ingredients.
  21. I am not a chemist, but from what I have read and observed, I think the risk of copper poisoning from ceramics use is overstated. If you drink a liter a day of water that has up to 1.3 mg in it, and that is considered safe, any copper leaching out of a mug would be far less than this. I doubt a mug would have 1.3 mg of copper in the whole glaze application, let alone a lethal dose. People have been drinking vodka mules out of 100% copper cups, and we have not seen the new stories about these deadly cocktails killing consumers. That is because in order to get copper poisoning
  22. You handled this well by moving on, this allowed the learning and creativity to continue. If you took the bait to engage with her pettiness it would have taken away from the other students who were there to learn and create. My advice is refuse to let her in the group again. She has nothing to contribute to your class and if she makes other accusations or complaints, it takes your time away from students that appreciate the efforts you are making to teach them. I am sure you can find a better student to sit in her seat. If she complains or asks why, say "you called me a liar, you did
  23. Another approach to aging the handle is to take a walk outside with some sand paper and an x-acto knife and scratch and sand away some of the under glaze. Use fine sand paper at the end to get rid of any jagged spots. You can still add a wash to this afterwards if it needs it.
  24. Joseph, I just ordered a bag of chicken scratch after seeing your results. I have some wood fires coming up, but I usually fire reduction gas. Would the granite pop off and possibly hurt glazed pots around it at cone 10, or was it pretty stable? I don't want to risk hurting the other pots while experimenting.
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