John Post on mon 18 jan 10
Hi Paula,
Clay body is a big factor. Try it on several different kinds. White, =3D2=
0=3D
buff, dark, etc.
Test different thicknesses of glaze on a variety of pots or test tiles.
Try different percentages of iron. I did many line blends with a =3D20
variety of iron reds and I got the best results in the range of 8-12% =3D20=
=3D
iron oxide. The faster your kiln cools, the more iron you need. If =3D20
your kiln cools slower, you can use less. The iron has to precipitate =3D2=
0=3D
to the surface of the glaze so if the kiln cools slower it gives more =3D20=
=3D
time for the iron to do that.
Don=3D92t fire iron reds on the top shelf of an electric kiln, unless you =
=3D20=3D
put another shelf on top of it. The shelves act like giant heat sinks =3D2=
0=3D
and hold the heat near the pots. I never get good iron reds on the =3D20
uncovered top shelf of an electric kiln. Also don=3D92t fire low bowls =3D=
20=3D
and tall pots on the same shelf. Think of keeping work of the same =3D20
height on each shelf so the next shelf fits tight. This keeps the =3D20
heat packed in during cooling.
Some folks re-fire their iron reds with a bisque firing to get them to =3D2=
0=3D
turn more red. The theory here is that since the pots spend more time =3D2=
0=3D
in the critical range around 1800 degrees F where the iron reds =3D20
develop, the iron will have more time to precipitate to the surface. =3D20=
=3D
Sometimes this works, sometimes it makes the glazes too matt. Try it =3D20=
=3D
and see.
If you don=3D92t have to work specifically at cone 6, try firing hotter. =
=3D20=3D
One potter sent me some private emails that he or she gets the reddest =3D2=
0=3D
reds from my tomato red glaze at cone 9
Here is the schedule used...
I fired your best red recipe with a slight different schedule and
perhaps you may be interested in the results. These were fired to 2270
with a 30 minute soak, cone 9 touching, 10 just starting to bend. The
cooling is fast to 1850, soak 3 hours, then 50/hr to 1800, off there.
In the same kiln there were pots with Bailey's red, Tomato red(John
Britt's book), none did as well in this schedule!
For those who might want to know the recipe I use here it is...
+++++++++++++++++++++++++++++++++++++++++++++
+++ Post's Tomato Red w/spodumene +++
+++++++++++++++++++++++++++++++++++++++++++++
11% Frit 3134
11.8% Spodumene
7.9% Bone ash
6.3% Magnesium carb
7.9% Whiting
21.6% EPK
21.7% Flint
11.8% Nepheline syenite
--------
100 %
2% Bentonite
10% Red iron oxide
John Post
Sterling Heights, Michigan
:: cone 6 glaze website :: http://www.johnpost.us
:: elementary art website :: http://www.wemakeart.org
-----------------------------------------------------------------------
Hello John,
I ended up with a satin looking chocolate brown instead of =3D20
tomato red. It has a same quality overall with no variations as =3D20
interesting as a lump of baker=3D92s chocolate or day-old dog poop (I take =
=3D
=3D20
that back=3D85dog poop has a more interesting surface). I used a =3D20
hydrometer to get a reading of 50 when I mixed the glaze for dipping. =3D20=
=3D
I=3D92m thinking I have glaze too thick. Will thin and do more test =3D20
firing. I=3D92m new to glaze mixing and will gladly accept any advice. I =
=3D20=3D
love breaking glazes and want to develop rusty reds, pumpkin-oranges.
Paula
John Rodgers on mon 18 jan 10
I fire cone 6 electric mostly and I used a Coyote Saturated Iron glaze
on a big project - like 400 identical pieces - chalices - and was firing
20 units per shelf in a 24 in dia. kiln. The restricted air flow, and
the very, very, very slow cooling ( due to the very compact load) of the
2 or 3 pieces in the very center of the center shelf in each load
resulted in the most gorgeous dark glossy cranberry I have ever seen. I
have never been able to recreate those exact conditions again, and so
have not been able to repeat it. But my experience showed that those
beautiful cranberry reds can be achieved with a saturated iron glaze.
The other thing that I ALMOST achieved was an iron blue. I made the
glaze up using crocus martis and got a definite solid blue gray that
was slightly more blue than gray. I did that on one pot, and haven't
tried it again. Maybe someone might give it a try and get it to work. I
was just messing around, and I'm not sure how I put the base glaze together=
.
John Rodgers
Clayartist and Moldmaker
88'GL VW Bus Driver
Chelsea, AL
Http://www.moldhaus.com
John Post wrote:
> Hi Paula,
>
> Clay body is a big factor. Try it on several different kinds. White,
> buff, dark, etc.
>
> Test different thicknesses of glaze on a variety of pots or test tiles.
>
> Try different percentages of iron. I did many line blends with a
> variety of iron reds and I got the best results in the range of 8-12%
> iron oxide. The faster your kiln cools, the more iron you need. If
> your kiln cools slower, you can use less. The iron has to precipitate
> to the surface of the glaze so if the kiln cools slower it gives more
> time for the iron to do that.
>
> Don't fire iron reds on the top shelf of an electric kiln, unless you
> put another shelf on top of it. The shelves act like giant heat sinks
> and hold the heat near the pots. I never get good iron reds on the
> uncovered top shelf of an electric kiln. Also don't fire low bowls
> and tall pots on the same shelf. Think of keeping work of the same
> height on each shelf so the next shelf fits tight. This keeps the
> heat packed in during cooling.
>
> Some folks re-fire their iron reds with a bisque firing to get them to
> turn more red. The theory here is that since the pots spend more time
> in the critical range around 1800 degrees F where the iron reds
> develop, the iron will have more time to precipitate to the surface.
> Sometimes this works, sometimes it makes the glazes too matt. Try it
> and see.
>
> If you don't have to work specifically at cone 6, try firing hotter.
> One potter sent me some private emails that he or she gets the reddest
> reds from my tomato red glaze at cone 9
>
> Here is the schedule used...
>
> I fired your best red recipe with a slight different schedule and
> perhaps you may be interested in the results. These were fired to 2270
> with a 30 minute soak, cone 9 touching, 10 just starting to bend. The
> cooling is fast to 1850, soak 3 hours, then 50/hr to 1800, off there.
> In the same kiln there were pots with Bailey's red, Tomato red(John
> Britt's book), none did as well in this schedule!
>
> For those who might want to know the recipe I use here it is...
>
> +++++++++++++++++++++++++++++++++++++++++++++
> +++ Post's Tomato Red w/spodumene +++
> +++++++++++++++++++++++++++++++++++++++++++++
>
> 11% Frit 3134
> 11.8% Spodumene
> 7.9% Bone ash
> 6.3% Magnesium carb
> 7.9% Whiting
> 21.6% EPK
> 21.7% Flint
> 11.8% Nepheline syenite
> --------
> 100 %
>
> 2% Bentonite
> 10% Red iron oxide
>
>
> John Post
> Sterling Heights, Michigan
>
> :: cone 6 glaze website :: http://www.johnpost.us
> :: elementary art website :: http://www.wemakeart.org
>
>
> -----------------------------------------------------------------------
> Hello John,
>
> I ended up with a satin looking chocolate brown instead of
> tomato red. It has a same quality overall with no variations as
> interesting as a lump of baker's chocolate or day-old dog poop (I take
> that back...dog poop has a more interesting surface). I used a
> hydrometer to get a reading of 50 when I mixed the glaze for dipping.
> I'm thinking I have glaze too thick. Will thin and do more test
> firing. I'm new to glaze mixing and will gladly accept any advice. I
> love breaking glazes and want to develop rusty reds, pumpkin-oranges.
>
> Paula
>
>
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