Expert: Sam Kelly - 9/25/2008

Question
QUESTION: Hi ... although I've been firing electric kilns at the community college for a few years, I just recently purchased a Bailey Electric kiln.  For kiln and ware safety ... At what temperature do you recommend someone to open a kiln after firing either bisque or glaze? i.e. peep holes, crack the top, and open the lid?  Thanks so much ... Mary

ANSWER: Hi Mary,
There is a crystlobite change in the clay body at 200degC so never open a kiln up untill its below this, I usually wait untill 160degC and crack the door, this is for any firing. Totally open at around 100 but be carefull,especially with students.
The peep hole should only be used to watch the cones if that is the firing process you use. If you are quick you can have a quick look through it but wait untill about 240-260, understanding that cold air rushing in could cause a blowup.

Sam

---------- FOLLOW-UP ----------

QUESTION: Hi Sam ... My "new" kiln has completed 2-test cycles over the past few days, and yesterday I ran my first bisque (cone 06) firing.  In the one of the instruction books (of which there were three) it said to keep the top peep hole open and the vent running until after the kiln is completely cooled.  But, the Customer Service representative for the manufacturer said to "turn off the vent and close the peep hole after the program reached high temperature and "completed" the ramping heat cycle".  What are your thoughts for the vent and peep hole for a Bailey, Electric, Cone 6, Vented, kiln as it pertains to a bisque and/or glaze firing?  Thanks for your help.  Mary

Answer
BISQUE: Close all vents and peep holes at 600degC when heating up. On cooling down open peep hole under 200degC.

GLAZE FIRING: Peep hole open only to 400degC when heating up. On cooling down open peep hole under 200degC.

When a pot is being bisque fired there is still what is termed "chemical water" in the microscopic structure of the clay body. It's not until 600degC that this water is finally removed.

When glaze firing there has been a small amount of water retained from the glaze and having the peep hole open to 400degC is a precautionary thing that I do, it also lets the burning wax out of the kiln if you have used it during the glazing process.

I fire 3 electric kilns twice a week and the vents are never open, I use the peep hole(which is for watching cones)all the time. Experiment with the vent on your bisque firings though, a full load not completely dry might benefit with it open.

A new kiln is like a new car, you have to learn to drive it, once learnt it's easy.

Sam