Posted 10 December 2013 - 06:47 PM
I have a small kiln with similar controls and have been struggling for a year to get my glaze firing right. The biggest problem for me was not knowing what heating rate each number on the kiln controller related to - all the firing programs said things like 100oC and hour for X hours then FULL TO max temperature. I didn't know whether 100oC an hour was ON, 1,2,3, or 4. Though I knew it had to be down the lower end! While brush on earthenware glazes were fine with, for example 2 hours on 2 then FULL to 05 minibar in the kiln sitter, I had crazing problems with dipped/poured transparent glaze over and over again. My 40 litre top loader fired in 4-5 hours, which seemed on the quick side, but it had had all replacement elements when I bought it second hand, so I thought it was just super efficient,
Eventually I called in the kiln engineer who thought perhaps the thermostat (controller) had failed, but on testing, this was not the case. I borrowed a digital controller and was able to measure the temperature for each number on my manual kiln controller, as the kiln fired - and hey presto I have discovered that even number 1 on the controller, was firing at more than 100oC an hour. My crazing problem was the result of the kiln firing too fast in the early stages. At last! Problem solved. I've even refired a number of pieces that had crazed, this time going slowly (100oC / hour) to 600oC then full to 1100oC and they are fine.
The other thing that helped me was coming across a Potterycrafts document (online) called Programming your electric kiln, that explained, the firing process in a very straightforward manner, including the importance of the rate of temperature increase through 573oC. It also gave firing schedules for different clays and making techniques. My wheel thrown, white earthenware with dipped / poured glaze needed to be much slower than I had appreciated, and coupled with a 'vigorous' kiln, had caused me great frustration over the year. I don't want to invest in a digital controller for this small kiln as it will cost almost as much as I paid for the kiln itself, but I do now know the manual settings I need in order to get the right firing speed. Good luck with yours, I hope you get it sussed out quicker than I did,