Dave Finkelnburg on tue 1 sep 09
One of the frustrations of human communications is...names.=3DA0 What is po=
rc=3D
elain?=3DA0 What you choose to think it is.=3DA0 Defining, with some adject=
ive(=3D
s), more clearly what you mean may help communicate with others.=3D0AThe ad=
je=3D
ctive=3DA0ceramic industry=3DA0researchers use with porcelain is most often=
TRI=3D
AXIAL, as in "triaxial porcelain."=3DA0=3DA0A triaxial porcelain=3DA0is a m=
ixture=3D
of clay(s), feldspar and silica compounded to "mature" at a particular des=
=3D
ired firing temperature/time and displaying a desired color and translucenc=
=3D
y.=3DA0 "Mature"=3DA0in this case means vitrify to very low water absorptio=
n (t=3D
ypically less than 1/2% by weight).=3DA0 Electrical insulators, sinks and t=
oi=3D
lets, dinner wares and=3DA0tile can=3DA0all fit within this description.=3D=
A0 It'=3D
s no coincidence that industry forms these porcelain products primarily in =
=3D
molds rather than by some plastic process (jigger, jolly or throwing).=3D0A=
=3D
=3D0AThe previously mentioned article by Carty and Senapati is one of the m=
os=3D
t widely cited papers on porcelain and explains in very understandable lang=
=3D
uage how the ingredients convert to porcelain during the firing.=3D0A=3D0AT=
riax=3D
ial porcelains "typically" contain ~50% clay, ~25% feldspar and ~25% silica=
=3D
.=3DA0 Stonewares "typically" contain 85 to 95% clay with the remainder fel=
ds=3D
par. =3DA0Armed with this information it's not hard to see why stoneware bo=
di=3D
es=3DA0are usually much more plastic and consequently throw better than por=
ce=3D
lains!=3DA0 Both may and often do contain filler materials like alumina, ky=
an=3D
ite, grog, etc. to improve forming and/or fired properties.=3D0A=3DA0=3DA0=
=3D0ABone=3D
china, BTW,=3DA0 is also compounded from about 50% clay, but much of the g=
la=3D
ss phase derives from bone ash (calcium phosphate) rather than silica.=3DA0=
T=3D
he firing range of bone china is narrower than for triaxial porcelain.=3D0A=
=3D
=3D0AGood potting, even better communicating!=3D0A=3DA0=3DA0=3DA0=3DA0=3DA0=
Dave Finkelnb=3D
urg, saddened by Hank Murrow's note about David Stannard...=3D0A=3D0A=3D0A=
=3D0A =3D
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