We're going to fire some hand-made tiles to cone 4 or 5, but intend that they should be unglazed. Is there any reason to go through the usual cycle of bisque-firing, cool down, and then high fire if the ceramics will not be glazed? We were thinking that it would save time if we went directly to the high fire, perhaps with a hold at the lower temperature, or a very slow ramp rate from cone 04 on up.
Thanks
Paul
Paul, It certainly would save time and a lot of energy too. I see no reason at all to go through the twice firing process. I have to admit that I do not know to which temp cone 4 or 5 corresponds (In france we tend to loosely refer to the temp at which they fall rather than the number), but if the tiles are to be un glazed the only real worry that you would have is if you take the clay up to vitrification point without going slow enought to give time for carbon and sulphur burn out. This would result in bloating.
You could just attatch the tail end of a high fire onto a normal bisque fire.
Happy firing, Alistair.
St Amand en Puisaye, France.
E. Paul Wileyto wrote:
Follow the same regime for a Bisque firing, but extend the finish temperature to the desired cone. Remember to ventilate the kiln thoroughly until it ceases to smell sulphurous to prevent carbon build-up in the clay; this is the main cause of bloating and blistering. If you have a vent hole in the lid it really helps. Almost all US top loading kilns imported into the UK have this modification as standard.
Steve Bath UK
In article , E. Paul Wileyto writes
I think you can successfully once fire your tiles. I do something similar. I make toad houses out of red clay (cone 4-6) and I was bisque firing and then glaze firing although I didn't glaze them and I thought it would save time and energy if I could once fire them so I did and it works great. I even started putting a green glaze on the toad sprig on the roof and the archway into the door when the thing was bone dry then once fired to cone 6 and you can't tell the difference that I didn't bisque. Good luck with your project. Sandi
Steve Mills wrote:
Thanks very much for your help. We will let you know how it goes.
Paul (& Carol)
Red Deer wrote:
I have fired some very small, thin stuff glazed direct to high fire (1260).
Depending on how thick your tiles are, I would also be very careful to make sure they were dry all the way through - ie maybe dry-fire them to 120 C for a while to make sure all water is thoroughly out of them before going further up in temperature.
I am curious. What are these tiles for? Decoration? Why aren't you glazing them?
Marianne
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