Expert: Sam Kelly - 8/11/2008

Question
I work with adults with disabilities and we make ceramics to sell. I have noticed how easily these pieces seem to chip. We bisque to 02 and glaze fire to 06. All of our pieces are functionalware and foodsafe. We are always struggling with glaze problems and chipping of pieces as the go to craft shows. I would like to switch to stoneware but know little about it. What are the important things I need to know to switch our business over? Can I use the same molds, pour tables, kilns etc..? Thanks for any help on this subject, Karen

Answer
Hi Karen,
It's probably a typing error but the firing is the other way around, not bisque to 02 and glaze fire to 06, it's bisque to 06(1000degC)and fire to 02(1100degC).
Changing over to stoneware is not a problem, the main thing is if your kiln will fire to temperature, depending on clay type this is in the range of cone 5 to cone 9.
In Australia all stoneware is cone 9, In the US(cone5 to 9)Laguna Clay has a variety of casting slip bodies wether you mix your own or buy it already mixed.
http://www.lagunaclay.com/clays/slips/
The entire process is the same as you are doing now only the clay and glazes used will be stoneware instead of what you are doing now, earthenware 1100degC.
For stoneware use the same moulds, still bisque to cone 06, apply your glazes the same and fire. If you go to cone 9 and mix your own glazes here is a clear one I use that works on my clay.

Potash feldspar 1.670 kg
Kaolin Clay 0.600
Ball Clay 0.560
Whiting  1.200
Silica  1.980

This makes 6kg of base, add to this 9 Litres or water, if the material names are foreign to you any Pottery Supplier will know what they are.