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Re: clay firing question

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  • jdecker4art
    Greetings Cathy, The short answer is YES you can fire both the same time with no dangers - providing the pieces to bisque are made well and there is no danger
    Message 1 of 4 , Feb 11, 2012
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      Greetings Cathy,

      The short answer is YES you can fire both the same time with no dangers - providing the pieces to bisque are made well and there is no danger of them exploding (trapped air). I did this ALL THE TIME. While is is BEST to fire your clay to 04 (which is a higher temperature than 06 -- 05 is also hotter than 06) for a better fit, you can fire the bisque to 05 or 05. For years, I used Buff Clay (by Amaco) which is actually a lower firing Stoneware clay (I believe it was cone 5 or 6 - in this case cone 6 is hotter than cone 5). It just worked so well for hand building, I preferred it over any Earthenware clay I used -- although I often did use Terracotta, too (a low fire red clay).

      The problem you might experience is that your glazes may craze (slight cracks). Crawling (running off) occurs more if the bisque is fired too high rather than too low. Crawling (and shivering) may also occur is students handle their wares with too much lotion on their hands (I had that happen with one student's pot).

      You do not need to worry about the slight cracks in the glaze (usually only happens with the low fire gloss glazes) unless you intend to use the wares with food.

      You can minimize the crazing (slight cracks) by slowly cooling your kiln. Those little "pings" you hear as pieces cool is the glaze cracking.

      This is an accurate answer. I taught high school ceramics, middle school ceramics -- had a minor in Crafts in college -- and took several graduate courses. Believe it or not you can also single fire low fire clay (bisque and glaze at the same time), but I don't recommend that with student made projects.

      Your top shelves may get slightly hotter, but I always put the bisque projects on the lower shelves when fired with glazed ware so if pieces did "pop" the shards would not fall down on the glazed pieces.

      If the clay was well wedged -- and is absolutely bone dry - you will be fine. The elementary staff members ruined so many kids projects by NOT waiting till pieces were bone dry.... Then, of course, they blamed the exploding pots/works on the kids for not wedging properly. Drove me nuts, for sure - but there was nothing I could do about it (I would often get kids in middle school who never had a chance to glaze in elementary as their projects exploded every year!). If you fire them together VERY slowly, you will reduce the risk of explosions. The only student project that exploded for me was indeed MY fault as it wasn't completely bone dry all the way through (it was a sculptural piece).... I fired slowly...but not slow enough that time.

      Glaze shivering:

      This often happens if projects are not properly washed first. Are students rinsing their work before applying the glaze? -- Also, make sure they are not wearing any hand lotion.

      I used Amaco glazes....Never had issues with them other than slight problems with red glazes from time to time. Red HAD to be fired at cone 06 - any hotter, it would turn brownish and more transparent. Also, some of the red glazes could not be fired with various other colors (as a chemical reaction would cause the glazes to brown).

      How to fix your "Miami Pink" projects:

      If these are not for food, find a nail polish that is close to the color. Apply a couple coats -- and clear coat over if the glaze is a gloss color. I had quite a collection of nail polishes. We called them "Room Temperature Glazes". These came in real handy if a student only needed just a bit of red. Our "Room Temperature Glazes" could always be trusted to be the exact color we needed (smile).

      For more questions about glazing, do check out Dr. Marvin Bartel's site. I am pretty sure it is still online.

      Hope this clears up any confusion.

      Judy Decker

      > --- In art_education@yahoogroups.com, "allgaul" <allgaul@> wrote:
      > >
      > > Hi all,
      > >
      > > I have a few bone dry projects to do at cone 04 (I use Laguna Clay). I want
      > > to know if I could put them in with a glaze load at cone 06 and then refire
      > > them with glaze at 06 again. Has anybody tried this and does it compromise
      > > the rate of shrinkage and then lead to glaze shivering problems.
      > > Another question: I am using Duncan Envision glazes (06). I have a terrible
      > > time with Miami Pink shivering off, especially on corners and straight
      > > edges. It seems to stick ok on round projects.
      > > I have added clear glaze into it to see if that helps. What glaze brands do
      > > you use and are you happy with them?
      > >
      > > Thanks!
      > >
      > > Cathy
      > >
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