Lee on fri 16 sep 11
Don't reduce. Don't glaze the whole pot, only liner or not at all.
--=3D20
--
Lee Love in Minneapolis
http://mingeisota.blogspot.com/
"Ta tIr na n-=3DF3g ar chul an tI=3D97tIr dlainn trina ch=3DE9ile"=3D97tha=
t is, "T=3D
he land
of eternal youth is behind the house, a beautiful land fluent within
itself." -- John O'Donohue
Michael Mahan on fri 16 sep 11
I'm getting ready to fire a load of pots made from a local clay mix that =
=3D
is
high in iron. I've successfully fired the clay to above cone 10, but
sometimes it bloats. At high temperatures, the clay turns cast iron black=
=3D
with hints of purple. I'm bisque-firing everything and will glaze some
pieces, and I plan to keep most of the high-iron clay away from the fireb=
=3D
ox.
I fire in a cross draft Manabigama.
I'm thinking of firing to cone 10 in the front and soaking there for seve=
=3D
ral
hours. Any thoughts on firing high-iron clays in wood kilns and avoiding
bloating in high-iron clays? I don't want a bunch of pots with unmelted a=
=3D
sh
on them.
David Woof on sun 18 sep 11
Hi Michael=3D2C
if you just must fire this clay to cone 10 in a 100% body form=3D2C try kee=
pi=3D
ng to as
much of an oxidation atmosphere as is possible in firing wood.
Natural deposits of native clay are usually a complex mineral material and =
=3D
I'm sure you have many elements besides iron in the mix.
Have you given it the acid test while in the raw state?=3DA0 Most likely yo=
u =3D
will have soluable fluxing materials as well as the iron to consider.
Have you considered using this clay as percentage additions to another body=
=3D
in line blends
to determine where the bloating starts=3D2C and long before the bloating=3D=
3B I=3D
'm sure you will find black coring in the body.=3D20
It doesn't sound like a good body for vessels of domestic utility at stonew=
=3D
are temps=3D2C except that a small addition may give some interesting effec=
ts=3D
.
The solubles may give you a self glazing (high fire "Egyptian paste") effec=
=3D
t if you let the pieces sit raw on the shelf for 6 weeks to 3 months.
I have gotten some interesting and unusual surfaces doing this with various=
=3D
percentage additions of up to 30% of a cone 14 "Fredricksburg body" I deve=
=3D
loped some years ago.
You might also explore using this local clay as a main ingredient in a slip=
=3D
glazing application=3D3B or exchange it for the Red Art or other slip clay=
s =3D
in an established glaze recipe and see what happens.
Keep us posted.=3D20
Best wishes for a good firing=3D2C
David Woof
______________________________________>
15. wood fire with high iron clay
Posted by: "Michael Mahan" mahanpots@RTMC.NET
Date: Fri Sep 16=3D2C 2011 4:18 pm ((PDT))
I'm getting ready to fire a load of pots made from a local clay mix that is
high in iron. I've successfully fired the clay to above cone 10=3D2C but
sometimes it bloats. At high temperatures=3D2C the clay turns cast iron bla=
ck
with hints of purple. I'm bisque-firing everything and will glaze some
pieces=3D2C and I plan to keep most of the high-iron clay away from the fir=
eb=3D
ox.
I fire in a cross draft Manabigama.
I'm thinking of firing to cone 10 in the front and soaking there for severa=
=3D
l
hours. Any thoughts on firing high-iron clays in wood kilns and avoiding
bloating in high-iron clays? I don't want a bunch of pots with unmelted ash
on them.
=3D
Ron Roy on mon 19 sep 11
Hi Michael,
Your problem may be in the way you bisque.
If the organics are not burned out properly they will produce carbon
monoxide which will reduce the red iron oxide to black. Red iron is
not a strong flux - black iron is and can lead to overfired iron
bearing clay.
The trick is to fire bisque to 04 and make sure there is plenty of
oxygen available during the crucial period from 700C up to cone 04 -
and don't fire too fast - I would say no faster than 100C.
Some forms may need more attention - like if you fire lids on, stack
pots rim to rim or make it difficult for oxygen to get to the organics.
Thick clay will also need special attention.
If you are bisqueing in a gas kiln make absolutely sure your
atmosphere is oxidizing - if wood burns with a flame then there is
oxygen present.
There are good explanations in the Hamer dictionary of the problem.
RR
Quoting Michael Mahan :
> I'm getting ready to fire a load of pots made from a local clay mix that =
is
> high in iron. I've successfully fired the clay to above cone 10, but
> sometimes it bloats. At high temperatures, the clay turns cast iron black
> with hints of purple. I'm bisque-firing everything and will glaze some
> pieces, and I plan to keep most of the high-iron clay away from the fireb=
ox.
> I fire in a cross draft Manabigama.
>
> I'm thinking of firing to cone 10 in the front and soaking there for seve=
ral
> hours. Any thoughts on firing high-iron clays in wood kilns and avoiding
> bloating in high-iron clays? I don't want a bunch of pots with unmelted a=
sh
> on them.
>
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