Formulating a Porcelain Digitalfire
There is another upside of ball clay worth mentioning. Ball clays contain free silica, so if there is significant ball clay in a recipe the silica can be reduced leaving room to add more clay for plasticity or feldspar for maturity. So the easiest way to increase the plasticity of the standard '25 Porcelain' is to add 2%3% raw bentonite.