Jon Pettyjohn on sun 22 mar 98
I'm having some problems balancing porosity against
plasticity in the ^6 clay we mix ourselves. I find
that to get the porosity down to a reasonable
(for functional work) level I have to use up to
30% feldspar, this together with a little Silica
keeps the clay content at around 60% only and
given the clays we're using just isn't plastic enough
for hand work.
Just did a test on the following recipe and got good
plasticity with the higher (80%) clay content but the
porosity measured 8% +.
^6 Stoneware (ox.)
Marclay (a local high firing red clay) 40%
Black Ball Clay 30
Cagayan Feldspar (a local soda spar) 15
Silica 200M 5
Unfortunately nepheline syenite is too expensive and difficult
to import, I'm wondering if it would be OK to add a little
Calcium or Magnesium in the form of whiting or talc as an
additional flux, these materials arer easily available and
cheap. Any other ways to go on this?
appreciate any thoughts from people mixing ^6 clays,