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Firing in an electric kiln

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  • Firing in an electric kiln

    I am an self taught potter so dont have any proper kiln training. I have a medium sized electric kiln running on a single phase supply. Im finding that I cannot make the temperature rise quickly (250 degrees per hour). After 700 degrees it starts slowing. Becasue of the this (I think) the heatwork (Im using orton cones) vs temperature reading on the controller become more and more diverged.
    My recent experiment found that at cone 05 the controller is reading 40 degrees lower, cone 6 45 degrees lower, cone 7 62 degrees lower......
    so my question is should I just set the controller for a lower temperature and go with the cones reading or should I aim somewhere in between. I know that I can go on experimenting but just wondering if any one else on a single phase supply has ponderings about heatwork? Any thoughts greatfully recieved.
    ps recently crazed a whole kiln full of earthenware glazed work (several different clays) guessing this might have been caused by over firing ....

  • #2
    I guess I'm lucky in a way as I don't have a controller on my kilns - I use mini bars and a kiln sitter. When the mini bar bends, the kiln switches off. I have to manually turn it up at each stage, which sometimes means getting up every 2 hours throughout the night if I'm on a deadline!

    But at least it's uncomplicated and I never have any problems (touch wood)!

    Sorry I can't help with your question.


    • #3
      Thanks for your reply. H


      • #4
        Hi. I know a little bit about kilns, digital controllers and firing.

        Can you supply a bit more information as I can't work out what your issue is i.e.

        What makes you suspect that your kiln is not firing 250°c every hour in the first part of your programme?
        What products are you using (clay and glazes) and what are the recommended firing temperatures, ramp times etc for those products - also, are they compatible?
        What programme settings have you entered into your controller?
        What kiln and controller do you have?
        Did you set the second half of your programme to fire slower?
        Why are you using cones with a digital controller?
        Were there issues with the fired results in your recent firings? Is this why you don't know whether to go with the controller readings or the cone readings ... or did you just decide to "experiment"?

        You mentioned that you recently crazed a whole kiln of different clays. Crazing can be caused by an incompatibility with the clay, underglaze and glaze. Different clays are likely to have different firing temperatures too. However, it could also be that you are firing too fast (it is best to do a slow "bake" initially ... up to 600°c ... we recommend 150°c per hour ... but you must find out what the recommended firing temperatures of the clay are). Finally, sometimes the viscosity of glaze (too think or too thin) can cause crazing.

        I can confirm that the single phase supply will not affect the performance of the kiln (assuming it has been fitted by a qualified electrician according who was provided with the right technical information for the kiln e.g. ampage, kw etc).

        Why not read all the articles on the attached link? It really helped me when I started in this business nearly 10 years ago. Firing Tips. You need to select one topic at a time from the drop down menu in the FIRING TIPS section. I hope this helps.

        I look forward to reading answers to some of my questions.

        Kind regards Jenny

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        • #5
          Hi Heather

          I agree with the sensible advice give to this issue from Jenny. I would also question why the combination of computer and cone? Comparing the heat alone with the performance of a witness cone does not take into account the length or soak time of the firing. Basically, do not worry about the temperature given on the computer, the cone cannot be questioned. It bends when it has received a sufficent compliment of heatwork, (time & temperature), so if the computer is telling you this is slightly off the temperature it was expecting, I expect this is due to the amount of time it has taken to get there.

          Does seem to me you're going a bit fast though? You want to get to 750C in 3 hours? That is a wee bit speedy for my liking...
          Also, the fact that the kiln is slowing at 700 may simply be that it cannot sprint up at the rate you have asked it to.

          Hope this helps.