Wesley Rolley on mon 22 oct 01
I have ordered and thrown a sample of the stoneware clay body that=20
Michael Wendt has formulated using his Helmer kaolin. I have also read =
the commentary on Digital Fire concerning plasticity that reference this=
=20
body (=20
http://digitalfire.com/education/shortarticles.shtml#RationalizingPlasti=
city )=20
I have some questions for Michael and chose this forum as the answer=20=
might be of interest to others. =20
Do you have any experience in single firing this body? If not, what=20=
might you expect as a result? What changes might I have to make in my=20=
glazes to adapt to the different shrinkage (dry and fired) as described =
on Digital Fire site? I base my glazes on Redart and oak ash. =20
Wes Rolley=20
Michael Wendt on mon 22 oct 01
Wes,
For many years, I single fired all my flower pots. I found the key to good
results with Helmer was to do the inside glaze first, one day, let dry and
then do the outside another day. The glaze formula I send out is an old
University of Idaho chun recipe modified with more clay, talc and nepheline
syenite. It fires glossy at cone 8, yet is not too runny even at cone 12 as
long as the oxides are kept low. The formula came from Frank Cronk at the U
of I and I don't know where he got it. My version has been tested by Alfred
Analytical and passed for metals release to drinking water standards which
are very stringent.
Chun (modified, no tin oxide)
Custer 28.3
flint 23.0
Helmer 14.0
whiting 7.7
nepheline syenite 7.7
talc 6.4
barium carbonate 6.2
gertsley borate or frit 3134 5.7
zinc oxide 1.0
floating blue is produced by 0.5% CoO, 3% TiO2
white is 10% added superpax
takes most colors well
works over the green Helmer body
Si:Al = 8.15
SiB:Al = 8.35
CTE= 7.1 X 10^-6/degree C according to Insight
The Helmer body is formulated to have the lowest possible drying and fired
shrinkage and so requires a very fast pacing to throw with it. It is not
forgiving and won't allow you to dawdle, but works great for large or small
pots.
How did it work for you Wes?
Regards,
Michael Wendt wendtpot@lewiston.com
Wes wrote:
I have ordered and thrown a sample of the stoneware clay body that
Michael Wendt has formulated using his Helmer kaolin. I have also read
the commentary on Digital Fire concerning plasticity that reference this
body (
http://digitalfire.com/education/shortarticles.shtml#RationalizingPlasti
city )
I have some questions for Michael and chose this forum as the answer
might be of interest to others.
Do you have any experience in single firing this body? If not, what
might you expect as a result? What changes might I have to make in my
glazes to adapt to the different shrinkage (dry and fired) as described
on Digital Fire site? I base my glazes on Redart and oak ash.
Wes Rolley
Wesley Rolley on tue 23 oct 01
>>>>>>>>>>>>>>>>>> Original Message <<<<<<<<<<<<<<<<<<
> The Helmer body is formulated to have the lowest possible drying and=20=
fired
> shrinkage and so requires a very fast pacing to throw with it. It is n=
ot
> forgiving and won't allow you to dawdle, but works great for large or =
small
> pots.
> How did it work for you Wes?
Michael,=20
I am probably not the best qualified to give an analysis of throwing=20=
properties, as most of my experience is with a single body whose fired=20=
(in my Skutt) color I particularly like. However, I will agree that you =
can not "dawdle". I found it very different in feel from what I was use=
d=20
to. It was easier to control form. I ended up with pieces that were=20=
slightly thicker than I like, but that is related to having a different =
feel. I am in the process of changing elements in the Skutt, recovering=
=20
from a trip up the Oregon coast, assimilating what I learned from=20
spending some time with Hank Murrow and so will not fire for a week or=
=20
so. However, if these fire as I hope they do, then I will have my=20
supplier mix up a batch to your recipe and experiment on a larger scale.=
=20
Wes =20
Ron Roy on tue 23 oct 01
I just checked the glaze below (version with frit 3134) and it does look
like a stable glaze - it certainly has enough silica and alumina.
It must be well melted to be stable so if you use it at cone 8 you might
want to have it tested for Barium release.
A substitution of Strontium Carb (4.5) for Barium (take out 6.2) will lower
the expansion a bit.
Probably no use in putting in the Zink Oxide if you are firing in
reduction. There is reduction at some stages even in oxidation firing -
especially if once firing - so even in oxidation firing it is probably
vaporized.
RR
>For many years, I single fired all my flower pots. I found the key to good
>results with Helmer was to do the inside glaze first, one day, let dry and
>then do the outside another day. The glaze formula I send out is an old
>University of Idaho chun recipe modified with more clay, talc and nepheline
>syenite. It fires glossy at cone 8, yet is not too runny even at cone 12 as
>long as the oxides are kept low. The formula came from Frank Cronk at the U
>of I and I don't know where he got it. My version has been tested by Alfred
>Analytical and passed for metals release to drinking water standards which
>are very stringent.
> Chun (modified, no tin oxide)
>Custer 28.3
>flint 23.0
>Helmer 14.0
>whiting 7.7
>nepheline syenite 7.7
>talc 6.4
>barium carbonate 6.2
>gertsley borate or frit 3134 5.7
>zinc oxide 1.0
>
>floating blue is produced by 0.5% CoO, 3% TiO2
>white is 10% added superpax
>takes most colors well
>
>works over the green Helmer body
Ron Roy
RR# 4
15084 Little Lake Rd..
Brighton,
Ontario, Canada
KOK 1H0
Residence 613-475-9544
Studio 613-475-3715
Fax 613-475-3513
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