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Runny glazes - fire to 06

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  • Judy Decker
    Greetings, Here is a post from Barbara (which is correct). Barbara is having trouble posting. Howdy, The teacher with the runny glazes is firing to cone 05,
    Message 1 of 1 , Mar 4, 2008
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      Greetings,

      Here is a post from Barbara (which is correct). Barbara is having
      trouble posting.

      Howdy,

      The teacher with the runny glazes is firing to cone 05, which is a
      lower temp then your suggested Cone 04. Firing to a higher temp won't
      prevent the runniness, if anything it could make it worse. My guess is
      that the glaze settled and wasn't reconstituted before its use. So
      when kids used it before, it worked OK, but the some of the fluxing
      components ("melting components") then settled in the bottom. Then
      when they used the bottom of the container they were applying a glaze
      that had too much of the flux, and for a turquoise glaze, there is a
      lot of cobalt which will flux. That makes the glaze run at a temp
      that it normally would not. It is important to read what the labels
      say and if a glaze container specifically mentions mixing it well or
      "some settling may occur" be sure and run the whole jar though a sieve
      (fine mesh) and adjust the water content to the right consistency
      (should flow like heavy cream). Then pour it back in and let the kids
      use it. If it then sits for a long time (esp over the summer), empty
      the whole container out and re-sieve, even if it is only half a jar
      left.

      The only other issue might be the kiln firing too long. Even if you
      don't go "over" (higher) the temp the glaze requires if you fire it
      too long (if the kiln holds at the final temp for a long time) that
      will make it over fire and can ruin glazes and clay bodies. If you
      find it is taking a lot longer to reach temp than it used to, say four
      or more hours longer than it used to, and it especially takes a long
      time to go the final couple hundred degrees, it could over fire. But,
      since you don't mention a problem with any other glazes, just the
      turquoise, I'd say that the large volume of cobalt in that glaze
      caused your problem when it "settled out."
      -------------------------------------------------------

      I fired all of my Amaco glazes to cone 06. If any glazes didn't fuse
      properly at the cone, I placed the pieces on the top shelf as my kiln
      fired hotter towards the top. I had very few glazes that needed to be
      fired to cone 05 (some Duncan Glazes needed 05).

      Always make sure your glazes are properly mixed. I used a blender for my glazes.

      Judy Decker
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