Expert: Sam Kelly - 5/9/2009

Question
QUESTION: Until recently I have always used cones for my firing. Now I have a computerised kiln. I have to program the firing sequence that I require. I am not sure of the process for firing to a cone 04 Bisque. ie the degrees per hour to take the temp up etc and the hold times. If you could help me I would we grateful. Thank you.

ANSWER: Hi Barbara, I am also in Australia, Coffs Harbour NSW.

Usually bisque is 06(1000DegC). You need to keep it to 50deg an hour for the first 4 hours, it's around 230 Deg that explosions occur.

That will bring it to 200DegC

Then 75Deg an hour for 3 hours, that will bring it to 425Deg, all organic material is now gone but molecular water still remains untill red heat which is 600Deg.

100deg an hour for 2 hours, you are now at 625Deg, all water is now gone and bungs can be put in(kiln closed)

150Deg an hour now untill final temp.

Put your cones inside, still use them, they don't lie, adjust your final temp to the cones.

Sam

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

QUESTION: Thanks Sam,

I probably forgot to mention I was refering to Hobby Earthenware clay. So bisque firing with a cone in the sitter is 04.

Regards

Barbara

Answer
Hi Barbara, I don't know what hobby earthenware clay is, however water is water and it must be removed slowly, follow what I have indicated and thier will never be any problems.

I don't know wether you hand build or not, but if you do the minutest air pocket between coils or what ever and thier will be 'KBOOM'

Sam