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douglas

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About douglas

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    http://www.atlantapotters.com
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    douglastobin

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    Georgia
  1. Reducing thermal conductivity

    Just spitballing here, as I have not tried this. If you used very soapy water for your slip, and used an electric mixer to foam/create bubbles, this might create air pockets which would be additional insulation. Or mixing in fine sawdust might play a similar role. Then dip the greenware in a thin slip to smooth out any surface irregularities.
  2. Re-Glazing - Firing Speed?

    I have re-fired on medium speed without incident, but it is safer to use the slow speed. We work in a community studio so re-fires happen at the same speed as regular firing, which takes around 11 hours, so our kiln is not heating up as quickly as yours is.
  3. Short Wood Fire Thinking

    If you are new, I would stick to smaller forms like you mentioned. You are more likely to get lots of small pieces in than larger ones. You may want to bring one or two large pieces just in case it is ok with the kiln lead. I sprinkle wood ash on my glazes if it is a short firing. That way even if you don't get much ash buildup, you will get some movement in the glaze. In general Shinos are good choices for glazes. Most woodfires get between cone10 and cone 14 so make sure your glazes are cone ten. Most people do a liner glaze on the pot interior. You can leave the outside bare, or dip the rim and maybe the top third of the pot in glaze so when the glaze drips it won't go all the way down to the kiln shelf. Use cone 10 clay. Ask your supplier what they recommend for wood. I've used Highwater Phoenix clay and liked it, but most people use stonewares with iron in them (Phoenix is a white stoneware. Delicate textures and carvings may get covered by ash, so you may want to use bold textures and carvings that can stand up to the ash deposits if you get them. Good luck and post photos when you are done.
  4. Iron

    Is anyone else freaked out with the casual way they are recommending cadmium stains? They caveat that any glazes for food use should be tested, but many/most potters just use recipes and don't send glazes out for testing. Maybe I am overreacting, I am not a chemist, but since even trace amounts can cause cancer or be fatal, this seems like a poor ingredient to recommend to independent studios. https://en.wikipedia.org/wiki/Cadmium_poisoning
  5. Iron

    It might be worth doing some small batches with new iron oxide, firing alongside the glaze using the old, and see if you get different results. I did not think iron oxide changes, but maybe it continues to oxidize over time, changing the color.
  6. Make your own saggar out of your reclaim clay -- that way you know what temperature it can reach, and you can make it the right size
  7. Shimpo 21 Rk-10 Questions

    I have an RK-2 which is an earlier model. I throw mostly with a brent now. The RK2 is really loud, I don't know if the RK-10 shares that problem. The upside to this design is the cone drive and motor are all mechanical. There are no circuit boards to fail, so if you are handy, you can fix this. Shimpo does not support these anymore, but it seems there are plenty of parts in the pottery suppliers hands. Mine handles 20lbs with no problem. If you want to throw really big it might not be up to the task. But this guy seems to make fairly large pieces on it. https://www.youtube.com/watch?v=c-99NPQ_gho#t=1m30s The pedal and hand throttle control the speed of the wheel, you can use either one. Since the pedal is attached to the wheel, you have zero options on repositioning where your foot goes.
  8. Not to pile on, but there are some people who still believe that fritted lead is safe, and these are people to avoid at all costs. They have strong opinions based on their beliefs and not facts. Contaminating your kiln with lead is only one of the possible ways they can hurt your business. https://digitalfire.com/4sight/hazards/ceramic_hazard_lead_in_ceramic_glazes_what_did_we_learn_368.html main takeaways: >It is amazing that there are still many misinformed users around the world who are complacent and just unaware. Many people today still believe that as long as fritted sources are used it is safe. This is obviously not true, PbO in a fired glaze is still PbO no matter what material sourced it. >Although lead can be used safely in circumstances where stringent testing and controls are in place, in general, there are too many variables to use lead safely in a small operation.
  9. Porcelain Survey

    Glazenerd, do you think the clay body would flash in wood, salt, or soda, or would it require flashing slips?
  10. Ouch sorry to hear that. My general rule with microwaves is never put anything in there if you care about it breaking. But when company is over, you never can predict who is going to grab that piece you really love and do just the wrong thing to it.
  11. The clay won't thicken objectively, but parts of the pot may increase its thickness relative to the rest of the pot during shrinkage. I think most potters have experienced trimming a foot, and after firing the bottom of the bowl expanded beyond the foot after firing causing it to wobble. https://www.youtube.com/watch?v=WH2MV5dEb1g#t=10m32s
  12. One thing I think we forget is that commercially produced tablewares also craze over time when used in the dishwasher. It takes longer but the stress of the heating element breaks down most glazes. What starts out shiny starts to look crackly over the course of a hundred washes. Not to say we should not strive for defect free glaze fit, but we are handmaking items, not manufacturing them. Personally, if a shino glaze crazes that can add to the beauty, but I get that some customers will not see it that way.
  13. Thanks Min, Mark, and Marcia! I seem to have attracted the attention of all the "M" names today . I'll try making some for my home studio.
  14. It looks like you don't have anywhere near enough stain in order to make the clay black. You may be able to break the stain down into smaller dots, but you are going to have white clay with black speckles unless you up the percentage of stain.
  15. The studio I learned in had a strict no plaster policy. The risks of plaster getting into clay and causing explosions or pop-offs after firing were drilled into all of us. Therefore when I use molds, I make them out of clay and bisque them. I use plaster to reclaim clay but never use scrapers on the plaster, just wedge clay and clean off occasionally. I see lots of respected potters using plaster bats or molds to throw plates, the seem to use ribs or trim tools to cut off excess clay and don't seem too worried about a stray speck of porcelain being scraped into the clay body. So I am suspecting I am overly cautious with using plaster. Can anyone share their experience of using plaster to throw with -- what precautions to take. Do you throw away excess clay in case there are porcelain particles, or do you reclaim it? What is the right level of care to take when working. Is there a shelf life to bats, where you need to stop using them or they will start to degrade and deposit plaster into your clay?
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