Dave Finkelnburg on wed 6 dec 06
John,
As a place to start, test a recipe in which you
replace silica with feldspar as needed to achieve
about 35% nepheline syenite...or, use enough soda spar
to get a similar amount of sodium and potassium...you
can use a glaze calc program to do this quickly and
easily. Potash feldspar is usual in the Alfred 4x25
recipe, and you need lower melting soda minerals at
cone 5/6.
Using your calculation program, you can look at the
free silica in the ball clay...it varies widely
depending on which ball clay you use...and you can
tweak the recipe a bit as you see whether you have a
high or low SiO2 ball clay.
If you REALLY want white, get low-iron ingredients.
If you want translucency, get low-titanium
ingredients (like Grolleg kaolin rather than EPK). To
some extent iron and titanium tend to go together.
:-(
For plasticity some postings in the archives favor
a SMALL amount of V-gum T or hectorite rather than 2
or 3% bentonite. All aid plasticity, but the latter
seems to promote shrinkage cracks and warping
problems. You may want to study the archives a bit.
Personally, I would always weigh the ingredients.
You may add significantly more silica and feldspar
than clays if you use volume measures.
Good potting!
Dave Finkelnburg
--- John Rodgers wrote:
> On Tuesday Sept 20, 2005 Mr. Mayor posted his 4X25
> white porcelain recipe.
> 25 epk
> 25 silica
> 25 feldspar
> 25 ball clay
> +++++
> 100
> That's lbs, volume, per cent - your choice.
>
> Knowing what range the Mayor works in, this is a
> cone 10 + clay body
> for sure.
>
> Any gurus out there have any idea how to get this
> down to a cone 6 body?
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John Rodgers on wed 6 dec 06
On Tuesday Sept 20, 2005 Mr. Mayor posted his 4X25 white porcelain recipe.
25 epk
25 silica
25 feldspar
25 ball clay
+++++
100
That's lbs, volume, per cent - your choice.
Knowing what range the Mayor works in, this is a cone 10 + clay body
for sure.
Any gurus out there have any idea how to get this down to a cone 6 body?
Or is it possible?
I would really like to have a very white porcelain clay body that I can
mix rather than buy ready made.
Thanks,
John Rodgers,
Chelsea, AL
I have the
Ivor and Olive Lewis on fri 8 dec 06
Dear John Rodgers,=20
My main suggestion is that your select materials that have the minimum =
of Iron oxide in their given analysis.
My second suggestion would be to avoid using Nepheline Syenite. There =
are two reasons. First, though only slightly soluble, this can lead to =
deflocculation problems and reduce plasticity. Second, Neph Sy. is a =
rock, not a single mineral. There is good reason to believe it has the =
properties of a Eutectic mixture which might account for the behaviour =
Alex Sola describes. This may depend on the proportions of three =
minerals, Nepheline, Soda Felspar and Leucite. If all three are present =
in a sample the Phase Diagram (K2O-Na2O-Al2O3-SiO2, Fig 786, p 265. =
Phase Diagrams for Ceramists. ACS) shows a melting point of 1020 Deg C.=20
Perhaps a better auxiliary body flux would be one of the higher melting =
point Frits. Choose one with minimal Soda in its composition and do a =
line blend with your felspar to get the mixture with the optimal fusion =
temperature.
Best regards and good wishes for success.
Ivor Lewis.
Redhill,
South Australia.
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