I am a newbie to ceramics.I inherited an old Harpers toploading kiln. Model 83,5T,L,E .Power 5,7 kw current 26 Amp Max operating tenp 1280 C Serial no 09-10-89. It has 2 dials each marked to cone 6. It is working ,the other day somebody switched it on by accident.Oops ! fortunately I discovered it in time. Anyway I am an art teacher and my Grade 10 learners made some clayheads with earthenware which I want to fire.I have done a lot of research and learnt about the candling stage where the kiln must be heated slowly.It is the firing schedule thereafter that worries me.How do I make sure the temperature is taken up slowly without cracking the heads? I also have those Orton cones to check the cut off temp.I just wish there is somebody out there with previous experience to guide me.Help will be appreciated and the Grade 10.s especially will be very pleased if their teacher does not ruin their heads
Harpers KilnOld manual for old kiln
Posted 17 August 2014 - 03:22 PM
Success also would depend on if the heads have a good wall even wall thickness. Is the kiln in the classroom? Is it vented?
How thick are the pieces and how long have they been drying?
A simple firing would be to turn the bottom circuit on low overnight with the lid propped open about an inch. Early in the morning and put the second circuit on low. 2 hours later turn it to medium. 2 hours later shut the lid and turn it on full blast. Then sit and wait until the cones goes down.
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Montana State University-Billings
Charter Member and Past President of Potters Council
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