Liz Gowen 1 on mon 24 oct 11
I tried again this week-end to get some copper reds in my 12 cu fiber
downdraft propane fired Geil kiln. This time I fired to ^6 many new glazes
also the glazes I used in oxidation at ^6 went in as a test. I did 1 hr. on
pilots to 250 then 1 hr. on the lowest setting with all burners lit to 750.
I then turned it up to the max as has been suggested on Clayart. Started
reduction at 1400 oxyprobe reading .55 till about 2100 then it started to
stall as usual. I moved the damper out slightly to get the temp to rise, an=
d
went back and forth into reduction via the oxyprobe till I got to 2190 cone
6 flat on the bottom and at 3 O'clock on the top. held it for 15 min. I
then shut it off until the temp dropped to 1888, about an hour and a half,
and relit it at about 5-6 on the gas gauge and pushed the damper in till go=
t
reduction on the oxyprobe. With the tiniest adjustments to gas or damper I
went from .25 to .75 so stayed at the .75. It did drift a bit. Did an hour
there and then dropped another 100 degrees F lowered the gas to 1-1.5 and
damper almost closed held for another hour then closed it off and shut it
down.
This am I opened the kiln to dry bubbly matt, black crusted glazes.
Are they over fired ? under fired? What is the black charred layer on the
licorice that chips away like burned bbq to reveal a lovely blue gloss
underneath. When I soaked for an hour at 1900 and 1800 ish to get a
reduction oxyprobe reading it was .2 or .7 with the .2 I had many inches of
flame out the top peep hole, with the .7 I had sooty smoke pouring out the
top peep hole. 2 glazes got this char on them both high iron or was it from
the smoke. Looks like it could be sandblasted off to see the nice blue
underneath. The copper red were pink again and matt except one interior low
inside of a bowl which was what I was looking for though the outside of the
same pot with the same glaze is pink. I will put some of this up on my blog
but am too frustrated right now. I just feel like I am never going to learn
to fire this kiln. I did an oxidation plate of all the glazes I tested and
all the glazes had good melt shiny when supposed to be the reds were
greenish blue as expected. Is there too much iron in the licorice from
mc6glazes to fire in reduction or is the black crusty crunchy soot thin
layer from too much reduction with 2 soaks. Are the mats from under firing =
,
over firing or are they calcium matt crystals? My kiln takes about 12 to 1=
5
hours to cool by itself so perhaps it doesn't need to be relit and held for
2 hours. If anyone is in the Delaware area that fires gas and I could bring
these pots over to see what another set of eyes thinks it would be very
helpful. I did put 4 pots in the test kiln and am firing to ^6 oxidation to
see if they gloss up (if under fired). Any thoughts or suggestions would be
appreciated before I go out of my mind....Liz Gowen
Eva Gallagher on mon 24 oct 11
When we slow cool we do it in oxidation - at .75 you were in very heavy
reduction. Once I inadvertently did a redux in the cool and got some pretty
strange results especially with the red iron glazes which turned greenish
quite a bit - and that was with what was probably not very heavy redux.
Eva Gallagher
http://newfoundoutpotter.blogspot.com/
http://www.valleyartisans.com/gallagher/Gallagher.htm
----- Original Message -----
From: "Liz Gowen 1"
To:
Sent: Monday, October 24, 2011 2:32 PM
Subject: help assessing ^6glaze firing R
>I tried again this week-end to get some copper reds in my 12 cu fiber
> downdraft propane fired Geil kiln. This time I fired to ^6 many new glaze=
s
> also the glazes I used in oxidation at ^6 went in as a test. I did 1 hr.
> on
> pilots to 250 then 1 hr. on the lowest setting with all burners lit to
> 750.
> I then turned it up to the max as has been suggested on Clayart. Started
> reduction at 1400 oxyprobe reading .55 till about 2100 then it started to
> stall as usual. I moved the damper out slightly to get the temp to rise,
> and
> went back and forth into reduction via the oxyprobe till I got to 2190
> cone
> 6 flat on the bottom and at 3 O'clock on the top. held it for 15 min. I
> then shut it off until the temp dropped to 1888, about an hour and a half=
,
> and relit it at about 5-6 on the gas gauge and pushed the damper in till
> got
> reduction on the oxyprobe. With the tiniest adjustments to gas or damper =
I
> went from .25 to .75 so stayed at the .75. It did drift a bit. Did an hou=
r
> there and then dropped another 100 degrees F lowered the gas to 1-1.5 and
> damper almost closed held for another hour then closed it off and shut it
> down.
> This am I opened the kiln to dry bubbly matt, black crusted glazes=
.
> Are they over fired ? under fired? What is the black charred layer on the
> licorice that chips away like burned bbq to reveal a lovely blue gloss
> underneath. When I soaked for an hour at 1900 and 1800 ish to get a
> reduction oxyprobe reading it was .2 or .7 with the .2 I had many inches
> of
> flame out the top peep hole, with the .7 I had sooty smoke pouring out th=
e
> top peep hole. 2 glazes got this char on them both high iron or was it
> from
> the smoke. Looks like it could be sandblasted off to see the nice blue
> underneath. The copper red were pink again and matt except one interior
> low
> inside of a bowl which was what I was looking for though the outside of
> the
> same pot with the same glaze is pink. I will put some of this up on my
> blog
> but am too frustrated right now. I just feel like I am never going to
> learn
> to fire this kiln. I did an oxidation plate of all the glazes I tested an=
d
> all the glazes had good melt shiny when supposed to be the reds were
> greenish blue as expected. Is there too much iron in the licorice from
> mc6glazes to fire in reduction or is the black crusty crunchy soot thin
> layer from too much reduction with 2 soaks. Are the mats from under firin=
g
> ,
> over firing or are they calcium matt crystals? My kiln takes about 12 to
> 15
> hours to cool by itself so perhaps it doesn't need to be relit and held
> for
> 2 hours. If anyone is in the Delaware area that fires gas and I could
> bring
> these pots over to see what another set of eyes thinks it would be very
> helpful. I did put 4 pots in the test kiln and am firing to ^6 oxidation
> to
> see if they gloss up (if under fired). Any thoughts or suggestions would
> be
> appreciated before I go out of my mind....Liz Gowen
>
>
John Britt on tue 25 oct 11
Liz,
Make your first reduction .75 (instead of .55) and skip all the striking =
=3D
stuff on the=3D20
way down. If you get the reduction early you don't have to do all that.=3D=
20=3D
What you ended up with was heavy reduction cooling.
Let me know if you need more,
John Britt Pottery
William & Susan Schran User on thu 27 oct 11
On 10/24/11 2:32 PM, "Liz Gowen 1" wrote:
> I tried again this week-end to get some copper reds in my 12 cu fiber
> downdraft propane fired Geil kiln. This time I fired to ^6 many new glaze=
s
> also the glazes I used in oxidation at ^6 went in as a test. I did 1 hr. =
on
> pilots to 250 then 1 hr. on the lowest setting with all burners lit to 75=
0.
> I then turned it up to the max as has been suggested on Clayart. Started
> reduction at 1400 oxyprobe reading .55 till about 2100 then it started to
> stall as usual. I moved the damper out slightly to get the temp to rise, =
and
> went back and forth into reduction via the oxyprobe till I got to 2190 co=
ne
> 6 flat on the bottom and at 3 O'clock on the top. held it for 15 min. I
> then shut it off until the temp dropped to 1888, about an hour and a half=
,
> and relit it at about 5-6 on the gas gauge and pushed the damper in till =
got
> reduction on the oxyprobe. With the tiniest adjustments to gas or damper =
I
> went from .25 to .75 so stayed at the .75. It did drift a bit. Did an hou=
r
> there and then dropped another 100 degrees F lowered the gas to 1-1.5 and
> damper almost closed held for another hour then closed it off and shut it
> down.
The kiln at school is 24 cu. Ft. Geil fired with natural gas.
I start gas pressure at a mark 1/2 between 0 - 1 on the gauge.
Hour later to 1 on the gauge.
Hour later to 2 on the gauge
Hour later to 3 on the gauge - the highest I ever go.
Damper is on the #3 mark
In addition to the etched marks on damper, I have pencil lines every 1/8".
Star about 830am - around 12pm I'm at 1700 - 1750, start reduction, push in
damper to 2 3/4 mark, oxyprobe is 750 - 800 (guess for you .75 - .80).
This is rather heavy reduction according to probe, but no flames or smoke.
No flame from bottom spy hole, but back pressure will lite newspaper held
inch away.
Around 1950 - 2000, pull out damper to 3.
Around 2100, damper out to 3 1/8.
Watching cones, top cone 5 starts bending, damper to 3 1/4.
If top is a cone ahead, I'll drop pressure to 2 3/4.
By 330pm, cone 6 firing is done, close damper, go home.
No relight, cools very slow.
Good shinos, reds, celadons.
Think you start reduction too early, try not relighting kiln.
Bill
--
William "Bill" Schran
wschran@cox.net
wschran@nvcc.edu
http://www.creativecreekartisans.com
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