Firing Greenware In A Glaze Firing?
Posted 12 December 2013 - 09:36 AM
I let a friend make a few bowls as a Christmas present for his wife, and I was planning/hoping to throw them in with the low fire (^06 ) glaze firing I have already planned. Being that he used a ^6 clay body, bisque firing them to ^06 seems permissible, although I usually do bisques at ^08. However, reading up on the question, I discovered that it is not a good idea to mix greenware and glaze ware in the same firing, even if they require the same temperature, do to the possibility of gasses produced by the greenware interfering with the glaze chemical reactions.
My question is this: how bad of an idea is it to do it anyway, being that all of my pots are glazed in a clear glaze with black and white underglazes?? He needs them by Christmas of course, and I do not have any additional greenware to fire at the moment. So ya see, I was hoping to save dollars (and greenhouse emissions) by not having to do an entire bisque firing for four bowls... Advice from all you smart potters out there would be very appreciated!! Thank you!
Posted 12 December 2013 - 09:50 AM
To avoid any potential issues from the bisqued items off gasing, just don't pack them very close, to the other glaze items.
Just make sure that the greenware bowls are completely dry. There's nothing worse than fining glazed pieces with chunks of bisqueware fused into them, from exploded wares. It's the main reason I don't fire both together in my classroom kiln. Everytime I decide to try, something that I thought was dry, had a thick spot I didn't know about and....disaster.
Posted 12 December 2013 - 09:27 PM
I have fired glaze and bisque together occaisionally too and except for the first time all is well. Had one pot blow out because I set the firing schedule to suit the glaze ware but thankfully no damage to other pots.
The beginning of the firing must be set for the benefit of the bisque so that all the chemical water is driven off slowly first, then the last part of the firing must suit the glaze so that there is time for the heat to even out in the kiln and mature the glaze....adds about 2-2.5 hours to my regular glaze schedule.
Also stack my bisque on the lower shelves so that if all the heatwork falls short then the glazes are not affected and it doesn't change much of anything for the bisque, also stacked this way any blowouts won't rain down on the glaze ware either.
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Posted 15 December 2013 - 06:46 PM
And Norm, regarding your comment about bisque firing temps: I fire at ^08 because its how I learned in school. I haven't had my own studio for long, so I am still stuck in this steep learning curve- always so much to learn in this field. I HAVE been having issues with pin-holing and crazing.... Perhaps I need to be bisquing at a higher temp?! Thank you for the advice.
Posted 15 December 2013 - 07:01 PM
Ask your clay supplier what their clay needs, they should know.
Posted 15 December 2013 - 08:47 PM
I bisque at cone 06 all the time. I normally would bisque at 07 ,but I am out of those cones and have lots of 06's. Unless you are experiencing pinholing, you don't need to fire any hotter.
Posted 18 December 2013 - 11:30 AM
Why not just load the four bowls at the bottom and shelf over them. It would be a waste of some space, but certainly nowhere close to firing the four bowls by themseves. This way, even if there was an explosion, the glazed wares would be shielded by the shelves. This would definitely give enough distance so that gas interaction would not be of issue.
Christopher Vaughn Pottery
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