I have an electric kiln and bisque fire to cone 04 on slow speed, and glaze fire to cone 6 (also slow). Is it really necessary to bisque fire on slow? I understand the reason for glaze firing on slow speed, but not bisque.
Thanks Betsy
Betsy: The only real reason to fire slowly is to get the piece(s) past the point of water conversion to steam at 100C (212F), and the silica inversion at 600C. Once these two points have been passed, you can fire as slowly or as fast as you like. I regularly fire to cone 10 in less than 7 hours (porcelain)
More important is slow cooling, especially through these two temperature points again.
Hope that helps,
It is very necessary to fire slowly in a bisque up until 600C. I increase temp by 100C an hour until 600C then I set my kiln to flat out with half our soak. That is as fast as it can go. If you go too fast in this first 600 degrees you will have cracking exploding and just general breakage. Glazing, unless you are doing crystaline glazes or similar slow firing is not necessary. I increase at 150C per hour until 300C then flat out with half hour soak. The important thing with a glaze firing is gaining the amount of heat work required for the glaze to mature. A cone is just actually measuring the heat work. So you need to calibrate your kiln, that is do a number of firings at your different temps or what you think is your desired cone with cones top bottom and middle. When you require a C6 you would have a cone 51/2 cone 6 and cone7 in all three places. When you have completed that you will have more idea what your kiln is actually doing.
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