Expert: Ti Phillips - 10/5/2008

Question
I am wondering if it is possible to combine some bisqeware and glazed pieces at one firing.  I realize that I should be firing one at cone 04 and one at cone 06 but I was told that I could actually fire bisque ware at 06---so, will it mess it up if I combine some glazed pieces with some bisque ware and fire at cone 06???

Answer
Dear Megan,

Thank you for your recent question. Yes, you can fire green ware to bisque and glaze ware at the same time! But let me explain the process so that everything will turn out fine.

I am guessing at this, but because it is commonly the norm, I'm going to go with what is commonly used during glazing. Your glaze is probably a cone 06. Your clay manufacturer recommends that you bisque to cone 04. If this is correct, then you will want to fire to cone 06, not come 04. The reason being is that you want your glaze to mature and cone 04 is hotter than cone 06. So if you bring your glaze up to cone 04, you will over fire your glaze and ruin your work.

Bisque should be brought up to cone 04, but because you will probably glaze those pieces, only bringing them up to cone 06 will set the clay body to permanent. When you glaze and re fire the bisque ware, the glaze temperature will bring the bisque to maturing temperature and then the proper fusion with the clay and glaze will take place.

Now, if this is not the norm and your glaze cone maturing temperature is cone 04, you should not fire both bisque and glaze ware together for this reason. Because cone 04 is hotter than cone 06, firing green ware to bisque will cause the clay to begin to vitrify. If you wish to glaze these pieces in the future, the glaze will not be able to fuse with the clay.

You must remember that when valuing the temperature of cones, the 0# cones are hotter as the number gets smaller. Therefore, cone 04 is hotter than cone 06. Also remember that the glaze maturing cone is the most important. Underfiring or overfiring a glaze cone will ruin a glaze.

So, to recap,

If your glaze is a cone 06 glaze, then YES, fire both together.
If your glaze is a cone 04 glaze, then NO, do not fire together.

I hope this explanation helps you. If you have further questions, please feel free to contact me again.

Sincerely,
Ti Phillips
Earth Stoke 'N Fire Pottery Studio and Artist Retreat
www.earthstokenfire.com