David Pier on sun 13 mar 05
Hi All.
Matt Hoogland at Clay Planet let me know about the fine work that Daniel
has done on testing my porcelain. I thought I'd see what was being said on
Clayart. I'm not a regular Clayarter, so if you want me to read any
posting regarding this, please be sure to check the "To the original
poster".
A few points:
1) In the formulation of Pier Porcelain, high priority was given to green
strength. It has been my observation that flocculation might improve
workability, but it tends to lessen green strength, so I have generally
avoided it. While I did extensive testing on various formulations for
green strength, I haven't specifically tested the effects of flocculation,
so don't hold me to this.
2) Aging the clay certainly helps, but proper mixing of the materials in a
high shear mixer reduces the need for this. The people at Clay Planet are
the most fastidious clay mixers I have seen. This is the first time in ten
years I have had the confidence to use clay mixed by someone besides me.
3) High shrinkage often results in higher warpage and cracking, but this is
not the case in this body. As long as drying is not too rapid, this body
is very dimensionally stable during drying. Typically sized thrown objects
need no special drying care.
4) Another high priority in the formulation of this body was warp and slump
resistance. This is normally done by underfluxing or adding pure alumina,
both of which kill translucency. In this body, the stability was attained
by increasing alumina content without the addition of pure alumina, and
translucency and fired strenght were enhanced by a blend of non-traditional
fluxes (the feldspar content is less than 5%).
This body, and the matching compatible casting slip, were originally
formulated to meet my own demands. Since I sometimes throw shallow, small-
footed bowls over two feet in diameter, I needed both green strengh and
shape stability during firing. Since I primarily use brightly colored
transparent glazes, I wanted whiteness and translucency. My cast pieces
are sometimes fairly thin, so the shape stability during firing was also
essential in that case.
By using different fluxes, fillers, and plastisizers than are typical in
traditional porcelain bodies, I think I have attained a better combination
of whiteness, translucency, workability, green strength, shape stability
and fired strength than has previously been available.
One more note. Whiteness and translucency are two properties that work
against each other. In some exceptional cases, using exceptionally pure
ingredients, such as in Southern Ice porcelain, both are attained in large
measure. Usually, however, since translucency is letting you see more of
the body, the color in the body is intensified. But don't try throwing a
two foot bowl with Southern Ice!
David Pier
Daniel Semler on mon 14 mar 05
Hi David,
Thanx for all this information. As someone who is just beginning to delve into
claybodies this is very interesting. You have certainly piqued my interest
concerning some other aspects of your porcelain. More testing then I guess...
:)
Thanx
D
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