If at first you don’t succeed…

fire2.1  fire2.3

The next batch of items are in the kiln ready for my second ever glaze firing tomorrow. This includes the cups that I threw a few weeks ago. I’ve been doing a lot of research on how to slow down the cooling part of the cycle in the hope that I don’t end up with the same result as last time. I have also bought a handheld pyrometer and probe so that I can gauge more accurately the speed at which the kiln is heating and cooling.

If all goes well I will post the results and the firing schedule I have used on Monday.

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7 thoughts on “If at first you don’t succeed…

  1. Did you get a good cooling cycle sorted? I’m struggling with a firing down cycle to avoid subsequent cracking which I am assured (after loads of research) is due to cooling too fast. Have invested in a digital controller to try to resolve the problem but am getting my knickers in a twist on the program – which parts of the cycle to slow the cooling . Are they all the same as when firing up? Do I need to slow down all the way! I don’t really want to increase electricity costs unnecessarily!

    • Hi Celia, I now have a new kiln with a controller which fires more consistently and requires no cooling cycle for the clay/glazes that I’m using at the moment. However I did work out a cycle for the older kiln… Following the kiln reaching temperature and the kiln sitter shutting off I allow the kiln to cool on its own for a while, but checking the temperature regularly using a probe and pyrometer. Once the kiln cools to about 700˚C (well above the two critical points at 573°C and 226°C) I switch the kiln back on by raising the kiln sitter switch, pressing the button and then lowering the switch back gently so that it does not switch off again. I don’t have my firing notes with me at the moment but I think I set the temp dial at about 2.5, then slowly decrease the temp dial by half every couple of hours until reaching 0. I then switch off and leave to cool. This certainly worked the last few times I fired it. I also have found that now my throwing is better and my pots have a more consistent thickness throughout they seem to survive more often. One particular clay (a white stoneware porcelain mix) did not like one of my clear glazes and often caused spiral cracking. I changed to a different glaze and have not had problems since. As with all things to do with pottery I’m finding that there are many approaches to solving a problem. You just need to be patient. Perseverance works. Good luck. Let me know how you get on.

      • Thanks Juliet – you obviously went to far greater lengths doing it manually than I got round to before accepting my husband’s offer of Christmas controller! It’s reassuring that you’ve noted exactly the 2 temperatures I’ve found out about, though I’m not quite certain which of these was the cause of my problem. Belt and braces approach would lead me to do as you did, but via controller – go slowly from say 600oC to below 226oC. (I did read somewhere that set point down to 800o was relevant in some way also, but can’t find this again to check!) I’ll try this and then when I have some less precious pieces to glaze fire, perhaps just slow through quartz inversion, or perhaps speed it up between the 2, then slow again for cristobalite. Just worked out that with slow start and slow increase through 573o + all of the above is about 9 phases in the program!

        I suspect thicker bases and finer tops could also be part of my problem, so throwing practice can also go on the agenda – and a soak at the top maybe, though I don’t want to risk any crystallization in my transparent glossy glaze! Hey Ho – here we go again ‘2014 the year of practice’

        Thanks for your reply. Happy potting!

        Celia

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