Su Lowman on tue 2 mar 99
Although I have had some custom clay formulated to withstand greater thermal
shock than a off the shelf clay; I am still not fully satisfied with the
red-brown stoneware clay I am now using.
What I want is a clay that will fire large pieces of pottery 16" or greater
with more consistency. I am firing footed pottery on a silica sand sprinkled
on the shelf to act as ball bearings. The larger brown pots seem to crack in
the bisque as well as the high fire while the gray pots remain whole.
I doubt that undetected cracks in the greenware completely account for all
the problems.
Any help would be appreciated.
Thank you,
Dave
Dave & Su in Central Iowa USA, Zone 4/5 dasu@bonsaitrees.com
DaSu studio.. http://www.bonsaitrees.com
Su's page... http://www.netins.net/showcase/avatarstudio
Su Lowman on tue 2 mar 99
Although I have had some custom clay formulated to withstand greater thermal
shock than a off the shelf clay; I am still not fully satisfied with the
red-brown stoneware clay I am now using.
What I want is a clay that will fire large pieces of pottery 16" or greater
with more consistency. I am firing footed pottery on a silica sand sprinkled
on the shelf to act as ball bearings. The larger brown pots seem to crack in
the bisque as well as the high fire while the gray pots remain whole.
I doubt that undetected cracks in the greenware completely account for all
the problems.
Any help would be appreciated.
Thank you,
Dave
Dave & Su in Central Iowa USA, Zone 4/5 dasu@bonsaitrees.com
DaSu studio.. http://www.bonsaitrees.com
Su's page... http://www.netins.net/showcase/avatarstudio
"ronniebeezer on mon 16 dec 02
I am currently taking pottery lessons at a studio. I'm buying a Skutt
model KM1018 electric kilm to fire my pieces at home. I have never
fired anything so can you recommend a book for beginners, or can you
tell me how to start with firing greenware that eventually will be
glazed with cone 6 glaze.
Thank you, Ronnie
Charles Moore on mon 16 dec 02
Hi, Ronnie,
I think that Richard Zakin's "Electric Kiln Ceramics" is a really fine book.
Get the lastest (I think Second Edition). You should check with the
Potter's Shop, email: SBRANFPOTS.AOL.COM.
Charles Moore
Sacramento, CA
----- Original Message -----
From: "ronniebeezer "
To:
Sent: Monday, December 16, 2002 12:31 PM
Subject: firing
> I am currently taking pottery lessons at a studio. I'm buying a Skutt
> model KM1018 electric kilm to fire my pieces at home. I have never
> fired anything so can you recommend a book for beginners, or can you
> tell me how to start with firing greenware that eventually will be
> glazed with cone 6 glaze.
> Thank you, Ronnie
>
>
____________________________________________________________________________
__
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
Snail Scott on sat 22 feb 03
At 03:53 PM 2/22/03 -0800, you wrote:
>how many hours should I preheat before starting the bisque? also do I
need to leave the lid ajar or is removing the top peephole plug enough
ventilation for any moisture to escape? do I have to do the same procedure
when I glaze fire to cone 6?
1) Depends on how thick the work is. Anywhere from an
hour for really thin stuff to 4 hours for 3/4" thick,
I'd say. Longer for thicker. Also, bottoms dry slower,
especially on large-footed work.
2) I generally leave the lid propped a few inches during
candling, then shut it, leaving a peephole open for any
bisque or low-temp firing. I keep it shut for high fire.
3) Not really. Bisqued clay is usually strong enough to
withstand the escaping steam of any dampness it's
acquired since it was bisqued. One exception: If the
piece was covered in an underglaze (or glaze) before
bisque, it can have a sufficiently vitrified skin to
inhibit the escape of moisture. Take it slower for any
such work. Mostly, though, a quick candling (1/2 hour)
is enough, and can often be skipped entirely.
-Snail
ronnie beezer on sat 22 feb 03
Hello everyone,
Here I go again. I'm reading every information I can get my hands on about the correct way of using my kiln. It seems that the more I read the more confused I get. I want to fire a bisque load to cone 06. I have the option to use preheat for as long as I want. My question is: how many hours should I preheat before starting the bisque? also do I need to leave the lid ajar or is removing the top peephole plug enough ventilation for any moisture to escape? do I have to do the same procedure when I glaze fire to cone 6?
Ronnie
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william schran on sun 23 feb 03
Ronnie wrote: <bisque? also do I need to leave the lid ajar or is removing the top
peephole plug enough ventilation for any moisture to escape? do I
have to do the same procedure when I glaze fire to cone 6?>>
Ronnie - If you make certain your greenware is absolutely dry there
should be no reason for a preheat. Probably not bad idea to leave
the lid ajar until all steam escapes, but I only leave plugs out.
Just want to go slow on the heat climb at the beginning of the bisque
firing, until you start seeing some red heat, then go fast, but then
slow down at the end to make sure all organics are burned out.
You can go much faster with the glaze firing. Again make sure the
ware is dry, waiting 24 hours after glazing is not a bad idea. As for
firing speed, I fire my crystalline glazed work up to cone 6 in 3-4
hours. Of course the pots are rather thin.
Bill
Cl Litman on sun 23 feb 03
I've found that if I'm making wares of reasonable thickness and they are
well dry before I start firing then I just do a slow bisque fire which on
my digital kiln works out to about 10 hours to reach cone 06. When
working manually I took extra time at the low end.
I only preheat if I have thick wares (kids stuff), I haven't allowed it
enough time to air dry because I'm in a hurry, or I have enclosed spaces.
In that case I allow anywhere from 4 to 8 hours on low (before starting
the firing) where I make sure to keep the temp below the boiling point of
water. When I didn't have a digital kiln I left all the peeps out and
the lid propped for the preheat. I figured that the more air
circulation, the better for drying.
Cheryl Litman - NJ
cheryllitman@juno.com
> I want to fire a bisque load to cone
> 06. I have the option to use preheat for as long as I want. My
> question is: how many hours should I preheat before starting the
> bisque? also do I need to leave the lid ajar or is removing the top
> peephole plug enough ventilation for any moisture to escape? do I
> have to do the same procedure when I glaze fire to cone 6?
>
> Ronnie
RAYMOND W GONZALEZ on sun 23 feb 03
ronnie,
There are many things that you may consider when bisqueing. I tend to think
of the load and the thicknesses of the work in the kiln. when i am firing,
i use this formula: pilot one day, candle the next fire the third. that is
a slow firing for many. i always count on the fact that a slower firing is
always better. i was in an educational situation where were turning out a
lot of bisque where we would let the kiln canle for a couple of hours before
firing it. it was shady at times but almost all of the work came out. it
was too quick for me. i just loaded some sculptural work and let it candle
with the door open for 2 days before shutting it and letting it candle for
another day before i actually fired it off. hope this sheds a little light
on it for you.
reguards,
ray
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Arnold Howard on mon 24 feb 03
From: ronnie beezer
> I want to fire a bisque load to cone 06. I have the option to use
preheat for as long as I want. My question is: how many hours should I
preheat before starting the bisque? also do I need to leave the lid
ajar or is removing the top peephole plug enough ventilation for any
moisture to escape? do I have to do the same procedure when I glaze
fire to cone 6?<
I assume that pre-heat is a firing mode in your digital controller. The
length of time needed in pre-heat is a matter of experimentation; the
time needed varies depending on how much moisture is in the ware.
You should dry the ware as thoroughly as possible before placing it in
the kiln. It is expensive to use the kiln to dry ware. It takes a lot of
energy to turn the moisture into steam. Drying ware inside the kiln also
causes the kiln to rust.
If you do not have a downdraft kiln vent, you should leave the lid
propped in the extended position and peephole plugs out during pre-heat.
In the glaze firing, pre-heat is not necessary, because the moisture has
already been fired out of the clay.
Sincerely,
Arnold Howard
Paragon Industries, L.P.
www.paragonweb.com
Neil Fallon on tue 25 feb 03
I was accustomed to firing my bisque (cone 06) for about 5-6 hours. Most
firings were successful, but I have just been experimenting with a slower
firing formula that seems to "fit" better for me. Basically I candle the
kiln over night, then a full-on firing in the morning that takes another
three or four hours.
As for the lid open or not during the preheat or low firing period, I have
fired both ways without any noticeable difference. I tip toward keeping it
open to allow the air circulation.
Neil Fallon @ Rock Pond Pottery
Ron Roy on sat 1 mar 03
Hi Neil,
This may be OK for some clays but - if you run into pin holers or blisters
that get worse when refired - it's because you are firing too fast through
the temperature range where the organics burn out. Thats 700C to 900C and
make sure there is excess oxygen present to make sure no reduction is
happening. Some glazes will be sensitive to the problem - especially boron
glazes which seal over soon and trap any resident gases.
What can happen - and does - is any iron in the body can be reduced (turned
into a strong flux) and cause the over firing of some clays.
I recommend 10 hour bisque firings - the bonus is cleaner and more even
firings. Even this can be too fast deprnding on the clay and how thick the
ware is.
Remember this - it is going to come in handy some day.
RR
>I was accustomed to firing my bisque (cone 06) for about 5-6 hours. Most
>firings were successful, but I have just been experimenting with a slower
>firing formula that seems to "fit" better for me. Basically I candle the
>kiln over night, then a full-on firing in the morning that takes another
>three or four hours.
>
>As for the lid open or not during the preheat or low firing period, I have
>fired both ways without any noticeable difference. I tip toward keeping it
>open to allow the air circulation.
>
>Neil Fallon @ Rock Pond Pottery
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
RAYMOND W GONZALEZ on mon 10 nov 03
Over the past several weeks I have been in a debate with myself. Today, it
all came to a head with more questions...
First of all, my original question was, "is it possible to reoxidize an
already reduced glaze?" Meaning, If I were to refire a matured and properly
reduced reduction red glaze (Cone 10) in an oxidation kiln, would it change
the color of the glaze from red to clear or green? Unfortunately, I have
neither the need nor the desire to fire an oxidation kiln... Until today. I
have been taught that once a glaze is reduced, it changes from carbonate (in
the case of carbonates) to oxide. Thus, a carbonate looses oxygen, turning
it from Cu2O3 to Cu2O. Now the question is: is it possible to ADD the
oxygen back into the picture.
Further, I am curious of peoples firing cycles. I fire with a body
reduction from 08-04 and then in light reduction to 10 where I put it in
reduction again until 11 falls. (about 20 minutes) Unfortunately, I had to
go attend to business and trust someone else to reduce and shut off the
kiln. They got to the kiln late and only got to reduce for about five
minutes. I am wondering the AMOUNT of reduction and WHERE people reduce to
achieve a high fire reduction atmosphere. Basically... How do YOU fire?
I will find out, to some level, the answer to both questions tomorrow, when
I see the amount of reduction on a refire piece, but I am still interested
to find out...
Have a great day, thanks in advance,
Ray Gonzalez
Las Cruces, NM
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Ron Roy on fri 14 nov 03
Hi Ray,
It certainly is possible to change a reduction glaze by refiring - even to
only bisque temperature. Shinos get redder for instance.
My limited experience is with a tenmoku glaze - black when fired to 10R and
a remarkable difference when bisque fired again. I"m not sure if it's the
iron reoxidizing or crystals growing or maybe both.
RR
>First of all, my original question was, "is it possible to reoxidize an
>already reduced glaze?" Meaning, If I were to refire a matured and properly
>reduced reduction red glaze (Cone 10) in an oxidation kiln, would it change
>the color of the glaze from red to clear or green? Unfortunately, I have
>neither the need nor the desire to fire an oxidation kiln... Until today. I
>have been taught that once a glaze is reduced, it changes from carbonate (in
>the case of carbonates) to oxide. Thus, a carbonate looses oxygen, turning
>it from Cu2O3 to Cu2O. Now the question is: is it possible to ADD the
>oxygen back into the picture.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Laura Kneppel on fri 14 nov 03
Hi Ron,
You've got me curious now - what does the tenmoku look like after it's
been re-fired?
Laurie
Sacramento, CA
On Friday, November 14, 2003, at 11:28 AM, Ron Roy wrote:
> My limited experience is with a tenmoku glaze - black when fired to
> 10R and
> a remarkable difference when bisque fired again. I"m not sure if it's
> the
> iron reoxidizing or crystals growing or maybe both.
daniel on sat 15 nov 03
Hi Ron,
Also curious. What clay body are you using, white stoneware, porcelain ?
Photos would be cool if you have them.
I had a small piece made from Glacia porcelain which showed some beginnings
of crystal growth after a single ^10R firing.
Thanx
Daniel
Laura Kneppel writes:
> Hi Ron,
> You've got me curious now - what does the tenmoku look like after it's
> been re-fired?
>
> Laurie
> Sacramento, CA
>
>
> On Friday, November 14, 2003, at 11:28 AM, Ron Roy wrote:
>
>> My limited experience is with a tenmoku glaze - black when fired to
>> 10R and
>> a remarkable difference when bisque fired again. I"m not sure if it's
>> the
>> iron reoxidizing or crystals growing or maybe both.
>
> __________________________________________________________________________
> ____
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
> melpots@pclink.com.
Ron Roy on sun 16 nov 03
No photos and I don't know if I still have that tile - I would not be
surprised if I threw it out I disliked it so much - Liz saw it - maybe she
remembers better than I do.
It was on a cone 10 porcelain but I don't expect the clay under the glaze
would have much influence.
Crystal growth is related to glaze chemistry and cooling rate - there are
many glazes that develop crystals even when not slow cooled - you can
sometime see this happen with the same glaze in the same firing - the glaze
when stacked in the top will cool slower than the glazes in the bottom -
I'm sure having a glaze in a sagger will have the same result - of slowing
down the cooling enough to start crystals in some glazes.
There are some glazes that want a fast cool to prevent crystals from
forming - a Tenmoku glaze for instance - best to keep em at the bottom of
the stack - unless you want the crystals - them keep em at the top.
RR
> Also curious. What clay body are you using, white stoneware, porcelain ?
> Photos would be cool if you have them.
>
> I had a small piece made from Glacia porcelain which showed some beginnings
>of crystal growth after a single ^10R firing.
>
>Thanx
>Daniel
>
>Laura Kneppel writes:
>
>> Hi Ron,
>> You've got me curious now - what does the tenmoku look like after it's
>> been re-fired?
>>
>> Laurie
>> Sacramento, CA
>>
>>
>> On Friday, November 14, 2003, at 11:28 AM, Ron Roy wrote:
>>
>>> My limited experience is with a tenmoku glaze - black when fired to
>>> 10R and
>>> a remarkable difference when bisque fired again. I"m not sure if it's
>>> the
>>> iron reoxidizing or crystals growing or maybe both.
>>
>> __________________________________________________________________________
>> ____
>> Send postings to clayart@lsv.ceramics.org
>>
>> You may look at the archives for the list or change your subscription
>> settings from http://www.ceramics.org/clayart/
>>
>> Moderator of the list is Mel Jacobson who may be reached at
>> melpots@pclink.com.
>
>______________________________________________________________________________
>Send postings to clayart@lsv.ceramics.org
>
>You may look at the archives for the list or change your subscription
>settings from http://www.ceramics.org/clayart/
>
>Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
daniel on mon 17 nov 03
Hi Ron,
I realised after the post that the impression would be that I was chasing
the clay body for the crystals. I was actually interested in it because of
the colour. Tenmoku seems to go gloss black on white clays more than on iron
bearing so far as I've seen. Not that that is much - several clays and a
couple of tenmokus.
I agree that the cooling rate would have lead to the crystals. I was
intrigued by the re-fire to bisque having produced crystals. Seemed like it
had served the function of a slow cool. Interesting what you say about the
placement in the kiln. Could well have been the case with my little piece.
Thanx
D
> No photos and I don't know if I still have that tile - I would not be
> surprised if I threw it out I disliked it so much - Liz saw it - maybe she
> remembers better than I do.
>
> It was on a cone 10 porcelain but I don't expect the clay under the glaze
> would have much influence.
>
> Crystal growth is related to glaze chemistry and cooling rate - there are
> many glazes that develop crystals even when not slow cooled - you can
> sometime see this happen with the same glaze in the same firing - the glaze
> when stacked in the top will cool slower than the glazes in the bottom -
> I'm sure having a glaze in a sagger will have the same result - of slowing
> down the cooling enough to start crystals in some glazes.
>
> There are some glazes that want a fast cool to prevent crystals from
> forming - a Tenmoku glaze for instance - best to keep em at the bottom of
> the stack - unless you want the crystals - them keep em at the top.
>
> RR
>
>
>> Also curious. What clay body are you using, white stoneware, porcelain ?
>> Photos would be cool if you have them.
>>
>> I had a small piece made from Glacia porcelain which showed some beginnings
>>of crystal growth after a single ^10R firing.
>>
>>Thanx
>>Daniel
>>
>>Laura Kneppel writes:
>>
>>> Hi Ron,
>>> You've got me curious now - what does the tenmoku look like after it's
>>> been re-fired?
>>>
>>> Laurie
>>> Sacramento, CA
>>>
>>>
>>> On Friday, November 14, 2003, at 11:28 AM, Ron Roy wrote:
>>>
>>>> My limited experience is with a tenmoku glaze - black when fired to
>>>> 10R and
>>>> a remarkable difference when bisque fired again. I"m not sure if it's
>>>> the
>>>> iron reoxidizing or crystals growing or maybe both.
>>>
>>> __________________________________________________________________________
>>> ____
>>> Send postings to clayart@lsv.ceramics.org
>>>
>>> You may look at the archives for the list or change your subscription
>>> settings from http://www.ceramics.org/clayart/
>>>
>>> Moderator of the list is Mel Jacobson who may be reached at
>>> melpots@pclink.com.
>>
>>______________________________________________________________________________
>>Send postings to clayart@lsv.ceramics.org
>>
>>You may look at the archives for the list or change your subscription
>>settings from http://www.ceramics.org/clayart/
>>
>>Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
>
> Ron Roy
> RR#4
> 15084 Little Lake Road
> Brighton, Ontario
> Canada
> K0K 1H0
> Phone: 613-475-9544
> Fax: 613-475-3513
>
> ______________________________________________________________________________
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
Ron Roy on tue 18 nov 03
Hi Daniel,
Refiring to a lower temp to give crystals a chance to grow is fairly common
in industry I think.
If you have a kiln load of copper reds and some are red and some still
clear - you refire the clears in a bisque and they come out red - by giving
the ruby crystals a chance to form.
It's really the same as slow cooling - just holding at the temperatures
when the glaze is still soft enough so crystals will form. Once the glaze
"freezes" become a solid - crystals can no longer form.
If - when refiring - you go too high any crystals that have formed will
melt - and you will have to start all over.
When refiring the crystals will grow on the way up and on the way down -
till the glaze solidifies. Seem to me - if you held a glaze at the right
temperature long enough - and there was enough silica available - the
crystals would just keep growing.
Interesting subject - Taylor and Bull go into it a bit in Ceramics Glaze
Technology - it's out of print but you might find it in a library - and
there are 2nd hand copies around. One of the better books on glazes.
Tenmokus will go black on stonewares - need a little more heat and maybe a
thicker coat - nothing like porcelain to help melt a glaze.
RR
> I realised after the post that the impression would be that I was chasing
>the clay body for the crystals. I was actually interested in it because of
>the colour. Tenmoku seems to go gloss black on white clays more than on iron
>bearing so far as I've seen. Not that that is much - several clays and a
>couple of tenmokus.
>
> I agree that the cooling rate would have lead to the crystals. I was
>intrigued by the re-fire to bisque having produced crystals. Seemed like it
>had served the function of a slow cool. Interesting what you say about the
>placement in the kiln. Could well have been the case with my little piece.
>
>Thanx
>D
>
>> No photos and I don't know if I still have that tile - I would not be
>> surprised if I threw it out I disliked it so much - Liz saw it - maybe she
>> remembers better than I do.
>>
>> It was on a cone 10 porcelain but I don't expect the clay under the glaze
>> would have much influence.
>>
>> Crystal growth is related to glaze chemistry and cooling rate - there are
>> many glazes that develop crystals even when not slow cooled - you can
>> sometime see this happen with the same glaze in the same firing - the glaze
>> when stacked in the top will cool slower than the glazes in the bottom -
>> I'm sure having a glaze in a sagger will have the same result - of slowing
>> down the cooling enough to start crystals in some glazes.
>>
>> There are some glazes that want a fast cool to prevent crystals from
>> forming - a Tenmoku glaze for instance - best to keep em at the bottom of
>> the stack - unless you want the crystals - them keep em at the top.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
daniel on tue 18 nov 03
Hi Ron,
> If you have a kiln load of copper reds and some are red and some still
> clear - you refire the clears in a bisque and they come out red - by giving
> the ruby crystals a chance to form.
I think Tichane discusses stuff like this quite a bit in his book on Copper
Reds which is a good read.
>
> If - when refiring - you go too high any crystals that have formed will
> melt - and you will have to start all over.
I can't seem to recall but the impression I get is that this cannot go on
indefinitely. Ultimately some of the copper seems to volatilize and so at
some point trying to refire to a lower temp and get the colour to return
will fail due to insufficient copper being available. This also is
discussed, though I'd have to re-read it, in Tichane I think. It would be an
interesting test with a piece to fire it in cycles until it failed to go red
again.
>
> Interesting subject - Taylor and Bull go into it a bit in Ceramics Glaze
> Technology - it's out of print but you might find it in a library - and
> there are 2nd hand copies around. One of the better books on glazes.
I'll check it out.
>
> Tenmokus will go black on stonewares - need a little more heat and maybe a
> thicker coat - nothing like porcelain to help melt a glaze.
One of the tenmokus I use is plum coloured (best short description I can
give though I have photos on my website I think) on stoneware - never even
seen it try to go black. I need to try it on porcelain. Not in my view a
great tenmoku but ... Fired in reduction, so its composition though I
haven't tracked the difference yet.
I've been doing more porcelain lately and I notice that the glazes are
sharper (like everyone says) so your last comment is very interesting. Does
porcelain actually alter the way (speed, completeness etc. ) a glaze melts ?
Thanx
D
>
> RR
>
>
>> I realised after the post that the impression would be that I was chasing
>>the clay body for the crystals. I was actually interested in it because of
>>the colour. Tenmoku seems to go gloss black on white clays more than on iron
>>bearing so far as I've seen. Not that that is much - several clays and a
>>couple of tenmokus.
>>
>> I agree that the cooling rate would have lead to the crystals. I was
>>intrigued by the re-fire to bisque having produced crystals. Seemed like it
>>had served the function of a slow cool. Interesting what you say about the
>>placement in the kiln. Could well have been the case with my little piece.
>>
>>Thanx
>>D
>>
>>> No photos and I don't know if I still have that tile - I would not be
>>> surprised if I threw it out I disliked it so much - Liz saw it - maybe she
>>> remembers better than I do.
>>>
>>> It was on a cone 10 porcelain but I don't expect the clay under the glaze
>>> would have much influence.
>>>
>>> Crystal growth is related to glaze chemistry and cooling rate - there are
>>> many glazes that develop crystals even when not slow cooled - you can
>>> sometime see this happen with the same glaze in the same firing - the glaze
>>> when stacked in the top will cool slower than the glazes in the bottom -
>>> I'm sure having a glaze in a sagger will have the same result - of slowing
>>> down the cooling enough to start crystals in some glazes.
>>>
>>> There are some glazes that want a fast cool to prevent crystals from
>>> forming - a Tenmoku glaze for instance - best to keep em at the bottom of
>>> the stack - unless you want the crystals - them keep em at the top.
>
> Ron Roy
> RR#4
> 15084 Little Lake Road
> Brighton, Ontario
> Canada
> K0K 1H0
> Phone: 613-475-9544
> Fax: 613-475-3513
>
> ______________________________________________________________________________
> Send postings to clayart@lsv.ceramics.org
>
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Ron Roy on wed 19 nov 03
Hi Danial,
I don't think there will be much copper leaving at bisque temperatures -
the copper will be in the glaze and sealed over in a refire.
Tenmokus are black and orange by definition - plums are iron saturated
glazes - could it be there is enough iron in the body to turn a tenmoku
into a saturated iron red?
If that is the case do a line blend dropping the iron in the glaze and let
the body supply the amount of iron needed to get the black.
Yes - porcelain does alter the way a glaze melts - in fact helps to melt it
more. Is it all that spar or is it all that silica - or is it because
porcelains melt more - or maybe because there are fewer impurities? I don't
know the answer - maybe all 4 are factors. Maybe - because there is so much
KNaO in porcelain - which starts melting at about 800C - it's because the
porclain just starts melting the glaze sooner.
RR
>> If you have a kiln load of copper reds and some are red and some still
>> clear - you refire the clears in a bisque and they come out red - by giving
>> the ruby crystals a chance to form.
>
>I think Tichane discusses stuff like this quite a bit in his book on Copper
>Reds which is a good read.
>>
>> If - when refiring - you go too high any crystals that have formed will
>> melt - and you will have to start all over.
>
>I can't seem to recall but the impression I get is that this cannot go on
>indefinitely. Ultimately some of the copper seems to volatilize and so at
>some point trying to refire to a lower temp and get the colour to return
>will fail due to insufficient copper being available. This also is
>discussed, though I'd have to re-read it, in Tichane I think. It would be an
>interesting test with a piece to fire it in cycles until it failed to go red
>again.
>>
>> Interesting subject - Taylor and Bull go into it a bit in Ceramics Glaze
>> Technology - it's out of print but you might find it in a library - and
>> there are 2nd hand copies around. One of the better books on glazes.
>
>I'll check it out.
>>
>> Tenmokus will go black on stonewares - need a little more heat and maybe a
>> thicker coat - nothing like porcelain to help melt a glaze.
>
>One of the tenmokus I use is plum coloured (best short description I can
>give though I have photos on my website I think) on stoneware - never even
>seen it try to go black. I need to try it on porcelain. Not in my view a
>great tenmoku but ... Fired in reduction, so its composition though I
>haven't tracked the difference yet.
>
>I've been doing more porcelain lately and I notice that the glazes are
>sharper (like everyone says) so your last comment is very interesting. Does
>porcelain actually alter the way (speed, completeness etc. ) a glaze melts ?
>
>Thanx
>D
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Earl Brunner on wed 4 aug 04
I dropped by the art center this afternoon to check on some pots from a
firing done last week. My boss showed me a ware board that I had
accidentally left on the top of a Skutt kiln. I'm not sure which kiln it
was left on, but I fired a bisque to 1800 F. in one kiln and a cone 6 glaze
in the other. The ware board was 3/8th inch plywood. It had charred almost
all of the way through the board. I don't know why it didn't flash into
flame. Fortunately the kiln building is a cinderblock structure with little
else to burn....
Earl Brunner
Las Vegas, NV
Joseph Bennion on thu 5 aug 04
Earl,
I did something like that once at BYU. I put a large square painted
plywood shelf under an octagonal electric kiln down in the art ed
studio. Between the kiln and the wood was a course of fire brick and a
bed of sand. I figured it was enough to insulate it. After two years of
use I was taking the kiln out and found that the shelf had a round burn
spot on it in the dimensions of the kiln bottom. In some places the
wood was barely charred. In others it was burned through several layers
of the plywood. It looked kind of cool but I threw it in the dumpster
and was glad it hadn't burned down the art building along with my
career as a student.
A year or so later I attended the opening of a faculty art exhibit.
Alex Darais had fished that board out of the trash placed one 1/8 inch
yellow square and a 1 inch circle of red on it and framed it up glass
and all. He titled it "In the Last Days". It is featured as plate 48 in
his book "Little Bird". Isn't that just like him? I'd give anything to
have that piece of art now.
Joe the Potter
--- Earl Brunner wrote:
> I dropped by the art center this afternoon to check on some pots from
> a
> firing done last week. My boss showed me a ware board that I had
> accidentally left on the top of a Skutt kiln. I'm not sure which
> kiln it
> was left on, but I fired a bisque to 1800 F. in one kiln and a cone 6
> glaze
> in the other. The ware board was 3/8th inch plywood. It had charred
> almost
> all of the way through the board. I don't know why it didn't flash
> into
> flame. Fortunately the kiln building is a cinderblock structure with
> little
> else to burn....
>
>
>
> Earl Brunner
>
> Las Vegas, NV
>
>
______________________________________________________________________________
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
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>
> Moderator of the list is Mel Jacobson who may be reached at
> melpots@pclink.com.
>
=====
Joseph Bennion PO Box 186 Spring City, Utah 84662 435-462-2708 www.horseshoemountainpottery.com
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william schran on thu 5 aug 04
Earl wrote:>..... check on some pots from a
firing done last week. My boss showed me a ware board that I had
accidentally left on the top of a Skutt kiln.... The ware board was
3/8th inch plywood.
It had charred almost all of the way through the board.<
Glad your forgetfulness did not result in a disaster.
Here are some simple rules/guidelines I drum into my students heads
regarding kilns/firing/safety:
1. Never, ever go away and leave a kiln to fire/shut off by itself -
NEVER, no excuses!
2. ALWAYS fire with witness cones. Yeah, you got a programmable kiln
with kiln sitter & limit timer.
That's just 3 things that can break down/go wrong, and "the glazes
didn't come out like they should, but I don't know what temperature
the kiln got up to". Quit being lazy!
3. Never, ever put ANYTHING on top of a kiln, even when it's off! It
will be come a habit that WILL end in disaster one day.
These are just common sense things to me. Sometimes sense is rare,
not very common.
Bill
claybair on thu 5 aug 04
Another reason to use hardibacker boards.
I'm glad to hear no damage was done!
Gayle Bair
Bainbridge Island, WA
http://claybair.com
-----Original Message-----
From: Earl Brunner
I dropped by the art center this afternoon to check on some pots from a
firing done last week. My boss showed me a ware board that I had
accidentally left on the top of a Skutt kiln. I'm not sure which kiln it
was left on, but I fired a bisque to 1800 F. in one kiln and a cone 6 glaze
in the other. The ware board was 3/8th inch plywood. It had charred almost
all of the way through the board. I don't know why it didn't flash into
flame. Fortunately the kiln building is a cinderblock structure with little
else to burn....
Earl Brunner
Las Vegas, NV
Earl Brunner on fri 6 aug 04
I'll go with number 3 as a good idea. Number two I do periodically to check
for temperature creep as the pyrometer probe ages. But number 1 ain't gonna
happen. No body is going to pay me to stick around and monitor a 16 hour
glaze fire at $20 something per hour.
The best I can do is not have anything to burn in the area, and that one 10
inch by 20 inch ware board was literally the only flammable material in the
building. The kiln building is concrete and metal- nuthin else.
I've asked this before, and no one on this list has been able to give me an
instance when a computer fired kiln malfunctioned and did a Cherynobl. In
EVERY instance where WE have had failures, the computers have shut the kilns
down, NOT over fired them.
Earl Brunner
Las Vegas, NV
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of william schran
Sent: Thursday, August 05, 2004 8:52 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: firing
Earl wrote:>..... check on some pots from a
firing done last week. My boss showed me a ware board that I had
accidentally left on the top of a Skutt kiln.... The ware board was
3/8th inch plywood.
It had charred almost all of the way through the board.<
Glad your forgetfulness did not result in a disaster.
Here are some simple rules/guidelines I drum into my students heads
regarding kilns/firing/safety:
1. Never, ever go away and leave a kiln to fire/shut off by itself -
NEVER, no excuses!
2. ALWAYS fire with witness cones. Yeah, you got a programmable kiln
with kiln sitter & limit timer.
That's just 3 things that can break down/go wrong, and "the glazes
didn't come out like they should, but I don't know what temperature
the kiln got up to". Quit being lazy!
3. Never, ever put ANYTHING on top of a kiln, even when it's off! It
will be come a habit that WILL end in disaster one day.
These are just common sense things to me. Sometimes sense is rare,
not very common.
Bill
____________________________________________________________________________
__
Send postings to clayart@lsv.ceramics.org
You may look at the archives for the list or change your subscription
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Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
Ron Roy on sun 8 aug 04
Hi Earl,
I have heard the breakers can weld shut - if it happens at the end of the
firing - would it not keep going?
Perhaps - when there are more controller in use we will start to see some
problems - I can't imagine a mechanical device not failing sometime.
If you are really interested - I know some one at Orton who might be able
to shed some light.
RR
>I've asked this before, and no one on this list has been able to give me an
>instance when a computer fired kiln malfunctioned and did a Cherynobl. In
>EVERY instance where WE have had failures, the computers have shut the kilns
>down, NOT over fired them.
>
>Earl Brunner
>Las Vegas, NV
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
William Melstrom on mon 9 aug 04
They aren't called breakers, they are called relays (there is a difference),
and they absolutely CAN stick in the closed, or "on" position. I have had
it happen twice to me, on two different computer controlled Skutt kilns.
The type of relay is commonly called a "cube" or "clear cube." Both times,
all I had to do was rap on the controller box to un-stick the relay (they
did not "weld" shut).
This happened on zone-control, 3-ring, 10-sided kilns. Each ring has its
own relay, so I am 3 times as likely to have this sticking problem occur.
Fortunately, only one zone got stuck -- the odds of two or three relays
sticking during the same firing must be astronomical.
Also, fortunately, a single ring stuck "on" is not enough to even come close
to a melt-down.
I do only crystalline firings. Each mishap was extremely educational
regarding crystal growth and formation, i.e. I learned from using what
turned out to be a bizarre firing profile that I never would have
intentionally programmed in. One stuck relay occurred during my "peak"
temperature, and one occurred during my final "soak," and both were stuck
for a few hours before I discovered them. One happened with a fairly new
clear cube, and I just decided to keep using it, not even replacing it. I
did tell Skutt, however, and they gave me 3 new relays, both times.
I have since moved the controller from the kiln, and mounted it to the
wall -- Being removed from close proximity to the kiln's heat greatly
reduces the chance of a relay sticking, in my opinion.
Skutt now offers relays with mercury switches, which are MUCH more reliable.
If you are worried, ask for them.
Before becoming a potter, I was a US Navy electrician for four years doing
lots of control work, and was a Union electrician for 12 years, doing a lot
of industrial work, so I think I know what I am saying.
William Melstrom
Austin, Texas
www.handspiral.com
william@handspiral.com.
----- Original Message -----
From: "Ron Roy"
To:
Sent: Sunday, August 08, 2004 11:34 PM
Subject: Re: firing
> Hi Earl,
>
> I have heard the breakers can weld shut - if it happens at the end of the
> firing - would it not keep going?
>
> Perhaps - when there are more controller in use we will start to see some
> problems - I can't imagine a mechanical device not failing sometime.
>
> If you are really interested - I know some one at Orton who might be able
> to shed some light.
>
> RR
>
>
> >I've asked this before, and no one on this list has been able to give me
an
> >instance when a computer fired kiln malfunctioned and did a Cherynobl.
In
> >EVERY instance where WE have had failures, the computers have shut the
kilns
> >down, NOT over fired them.
> >
> >Earl Brunner
> >Las Vegas, NV
>
> Ron Roy
> RR#4
> 15084 Little Lake Road
> Brighton, Ontario
> Canada
> K0K 1H0
> Phone: 613-475-9544
> Fax: 613-475-3513
>
>
____________________________________________________________________________
__
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
>
Rod Wuetherick on mon 9 aug 04
Earl,
Here in Vancouver A computer controlled skutt failed. They have the shelves
and the molten mass of whatever used to be shelves and pots at our local
supplier here in Vancouver. I think they are brought out to show people that
yes electronics fail. That is why you always on anything electronic,
mechanical, etc. You will see the letters MTB that's the manufactured
telling the Mean Time -> Failure.
Everything is possible,
Rod
William Melstrom on tue 10 aug 04
Earl Brunner wrote:
Now that you mention it, one of our relay cubes DID stick in the on =
position
awhile back, it happened during a controlled cool down and the =
temperature
climbed, which caused the kiln to shut down. We only fire on ramp =
schedules,
I wonder if the kiln would exceed the max. temperature or would it error =
out
and shut down?
Earl, this does not make complete sense to me. Yes, the controller =
would sense an error, and "shut down," but the relay would STILL be =
CLOSED ("on") !!! and supplying power to the coil! -- even though the =
display might be flashing "idle" or "error." A timer is a really good =
idea, or do an expensive up-grade and get mercury switches, which =
requires a whole new circuit board.
William Melstrom
Austin, Texas
www.handspiral.com
william@handspiral.com
Roger Korn on wed 11 aug 04
Ron Roy wrote:
Hi Earl,
I have heard the breakers can weld shut - if it happens at the end of the
firing - would it not keep going?
Perhaps - when there are more controller in use we will start to see some
problems - I can't imagine a mechanical device not failing sometime.
If you are really interested - I know some one at Orton who might be able
to shed some light.
RR
>>I've asked this before, and no one on this list has been able to give me an
>>instance when a computer fired kiln malfunctioned and did a Cherynobl. In
>>EVERY instance where WE have had failures, the computers have shut the kilns
>>down, NOT over fired them.
>>
>>Earl Brunner
>>Las Vegas, NV
>
>
If a relay (contactor or mercury displacement relay) or SSR (solid-state
relay) is used as the only disconnect to the power mains, the
possibility of failure to turn off exists. With a contactor, this is
minimized by using two contacts in series with each pole of the switch
and switching both poles, so that a failure would require four contacts
to weld shut. With a mercury displacement relay, the actuator that
pushes the mercury into contact with the conductors would have to seize
so firmly that the return spring could not open open the actuator. With
a SSR, closed failures can also occur.
In all three cases, the control computer has no way of preventing the
failure, since the switching device actuated by the computer is what fails.
Even Cone-sitters can fail to operate properly. All of these failures
are rare (I haven't seen them happen), but still possible. The only
sure-fire (arghhh!) solutions are to be present when the kiln is
supposed to shut off or to design the kiln so that it can survive
full-on operation for an infinite period of time.
I recommend the first of these solutions, since the second one means
that the kiln will take a long time to reach its design temperature, or
that the design temperature be significantly lower than the peak
temperature reached in the "full-on forever" case.
Hope this helps,
Roger
--
McKay Creek Ceramics
In OR: PO Box 436
North Plains, OR 97133
503-647-5464
In AZ: PO Box 463
Rimrock, AZ 86335
928-567-5699
claywomn on fri 5 nov 04
When firing my porcelain to Cone 9 the clear glaze turned out very nice =
but the work slumped - so I backed off and fired to Cone 8 with an 8 =
minute hold - the glaze was beautiful and the works held their forms. =20
Holding for a few minutes seems to give time to even the temp in the =
kiln but doesn't mean it goes to the next cone in temp/time. I've used =
the "hold" on my computerized kiln up to 15 minutes to get a richer =
color in some glazes. Ramping down is my next step!!
Barbara
In semi-snowy Upstate NY
Shelly on tue 28 jun 05
I have an older model (80s) AMACO electric kiln. It's firing unevenly,
too hot at the top, and barely reaching cone on the bottom. In the past,
I've been able to put shelves at the top to keep the heat down, but now
I'm firing some larger pieces, and don't have the ability to do that. I'd
like to do a glaze firing soon, but am obviously worried about over/under
firing. Since I basically taught myself to fire, I could really use some
help. I'm planning to fire to cone 6, and have always relied on my kiln
sitter. I have a lot of difficulty seeing the cones through the peep
hole, even with goggles.
Arnold Howard on tue 28 jun 05
The kiln may be firing unevenly due to incorrect elements. You could find
out by checking each element with an ohmmeter. Once you have ohmmeter
readings, a wiring diagram may help you determine if you have correct
elements. (When using an ohmmeter, it is very important to first unplug the
kiln.)
I would load the top of the kiln as heavily as possible and place only light
ware near the bottom. You might also try placing fewer shelves near the
bottom. You can improve heat distribution as much as half a cone by
rearranging load density.
Have you tried silhouetting the witness cones against a heating element on
the opposite side of the kiln? That makes cones stand out even at cone 10.
Also, the cones are difficult to see if they are too close to the peephole.
They should be at least 8" away.
Sincerely,
Arnold Howard
Paragon Industries, L.P., Mesquite, Texas USA
ahoward@paragonweb.com / www.paragonweb.com
From: "Shelly"
>I have an older model (80s) AMACO electric kiln. It's firing unevenly,
> too hot at the top, and barely reaching cone on the bottom. In the past,
> I've been able to put shelves at the top to keep the heat down, but now
> I'm firing some larger pieces, and don't have the ability to do that. I'd
> like to do a glaze firing soon, but am obviously worried about over/under
> firing. Since I basically taught myself to fire, I could really use some
> help. I'm planning to fire to cone 6, and have always relied on my kiln
> sitter. I have a lot of difficulty seeing the cones through the peep
> hole, even with goggles.
Shelly on tue 28 jun 05
Thank-you for your reply. I will have to get an ohmmeter.
Would you mind explaining a little bit more about the loading? As I said,
I'm self-taught, and know I have a lot to learn. I got better results
when I put taller pieces on the bottom of the kiln, but some of my pieces
are taller than 10" now, and I'm worried about stability of the
shelves....besides the fact that the tallest posts I have are 10". I'm
not sure what you mean by "light ware."
Arnold Howard on tue 28 jun 05
Load more ware in hot sections of the firing chamber and less ware in cool
sections. The greater the density of ware, the more heat required in that
section of the firing chamber. By changing the load balance inside the kiln,
you can alter the heat distribution by about half a pyrometric cone.
For instance, to reduce the heat in a hot section of the kiln, load short
pieces of ware that require extra shelves. Load fewer shelves in the cooler
sections of the kiln. The shelves are heavy and require extra heat energy.
It sounds like you have already been doing that since you placed a large
shelf near the top of the kiln. That shelf used up some of the excessive
heat in the top section of your kiln.
Sincerely,
Arnold Howard
Paragon Industries, L.P., Mesquite, Texas USA
ahoward@paragonweb.com / www.paragonweb.com
From: "Shelly"
> Would you mind explaining a little bit more about the loading? As I said,
> I'm self-taught, and know I have a lot to learn. I got better results
> when I put taller pieces on the bottom of the kiln, but some of my pieces
> are taller than 10" now, and I'm worried about stability of the
> shelves....besides the fact that the tallest posts I have are 10". I'm
> not sure what you mean by "light ware."
William & Susan Schran User on wed 29 jun 05
On 6/28/05 8:54 AM, "Shelly" wrote:
> It's firing unevenly,
> too hot at the top, and barely reaching cone on the bottom.
We had 2 HF 105 Amaco kilns at school prior to replacing with L&L's.
We used them primarily for bisque firing.
These kilns had 3 off/on switches - not much control, but they were great
for holding the heat for slow cooling.
I believe you're going to have to figure out how you can view the cones
during firing. When you see cone 6 bending at the top, you can turn the top
switch on and off, or if it's a low/med/hi switch, turn the top to med or
low, until the bottom cone 6 bends.
You simply can't rely on the kiln sitter to give out an accurate even
firing.
--
William "Bill" Schran
Fredericksburg, Virginia
William & Susan Schran User on wed 29 jun 05
On 6/28/05 9:56 AM, "Arnold Howard" wrote:
> I would load the top of the kiln as heavily as possible and place only light
> ware near the bottom. You might also try placing fewer shelves near the
> bottom. You can improve heat distribution as much as half a cone by
> rearranging load density.
I agree with Arnold about the distribution of the load.
Another thing to consider, if you have the bottom shelves sitting on the
kiln floor, try raising them up on 2" posts to see if that helps even out
the firing.
--
William "Bill" Schran
Fredericksburg, Virginia
Charles E Poarch on mon 15 aug 05
I'm looking for someone near Woodinville/Kirkland who fires small clay
sculptures. Can you help?
Earl Brunner on sat 23 aug 08
Yeah, my Geil is outside too. It is real touchy with breezes. A little breeze, out goes the pilot and off goes the kiln. I have the entire edge of the bottom so sealed, I worry about getting ENOUGH oxygen to the burners. It usually goes ok though.
Earl Brunner
Las Vegas, NV
----- Original Message ----
From: joyce
To: CLAYART@LSV.CERAMICS.ORG
Sent: Saturday, August 23, 2008 3:48:19 PM
Subject: Firing
Finally a day, while still hothothot, allowed a reduction firing!
That Geil has been loaded for at least a week. Everytime I
thought that we had a good start, the desert winds would
begin their ferocious attacks on any kilns anywhere within
reach. I find, though, that like this last load....... if the temp
can get to maybe ^06 ...... and IF all the windy spots (lots of
venturi action!) are pretty well covered THEN the whole thing
will probably be a GO. I love that moment when I know that,
yes, today it will happen!!
Fortunately, the wind doesn't seem to affect the electric
Cress so I filled it twice with pots, and even finished glazing
maybe half a new load for the bigger Geil........ and almost
completed a tall handbuilt pot that may require most of the
smaller Geil's space. I know that's not much by many claybuds'
standards, but for me, here and now....... it's just fine..... better
than just fine....... it's great.
joyce on sat 23 aug 08
Finally a day, while still hothothot, allowed a reduction firing!
That Geil has been loaded for at least a week. Everytime I
thought that we had a good start, the desert winds would
begin their ferocious attacks on any kilns anywhere within
reach. I find, though, that like this last load....... if the temp
can get to maybe ^06 ...... and IF all the windy spots (lots of
venturi action!) are pretty well covered THEN the whole thing
will probably be a GO. I love that moment when I know that,
yes, today it will happen!!
Fortunately, the wind doesn't seem to affect the electric
Cress so I filled it twice with pots, and even finished glazing
maybe half a new load for the bigger Geil........ and almost
completed a tall handbuilt pot that may require most of the
smaller Geil's space. I know that's not much by many claybuds'
standards, but for me, here and now....... it's just fine..... better
than just fine....... it's great.
One day I'll have a website ...... maybe soon.......... we'll see.
Then I'll take the opportunity to share pics with so many of you who
know how I salivate over your offerings. Folks who don't know
better think that we potters eagerly look at pics of any pots anywhere
because we're hoping to find something to copy. Not true, is it? We
simply enjoy looking at pots ...... all kinds of pots..... including jewelry!
Joyce
in the Mojave Desert of California U.S.A.
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