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How To Get More Even Elec. Firings?


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#1 clay lover

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Posted 03 May 2010 - 10:09 AM

I would appreciate some suggestions from more experienced potters on this.

I have a new Scutt 1027 Kilnmaster, hope it is OK to mention brands. I haven't been able to adjust things to get it to have cones even from top to bottom. I am new to firing at home and working my way through this. So far, I have fired with all peeps in and gotton a full cone cooler on the top shelf, with resulting glazes under developed. I put the cones in the same place each time and leave 2" above and below the themocouple with shelves. I use the Corelite shelving.

Next firing I took out the top peep at the suggestion of the Skutt tec guy, got the same looking cones, but that time the bottom was a full cone cooler, like I flipped the temps from top to bottem. Skutt guy said to slow down the last climb, I had set it for 200* per hour to 2195 with a 10 minute hold. He said that was too fast to get even temps through out.

Last night I unloaded a kiln that I has increased the peak soak from 10 minutes to 15 minutes and with a slower, 125* climb to peak, which I set at 22200*. I kept the peeps all in. The cones look more consistent, but I didn't have a top shelf, the only shelf was at mid way, with a full shelf of tall slender pieces with tall handles, so not real dense at the top.

I should add, I don't have a vent, the kiln is outside of my studio in a covered shed. the breeze blows through. The Skutt rep says I won't get even without having peeps out, but when I took them out, nothing improved, only reversed the cool area from top to bottom.
Any advice or similar experiences, I would love to hear. Thanks in advance!

#2 Chris Campbell

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Posted 03 May 2010 - 11:44 AM

That is one of the challenges of electic kilns ... They cool quickly ... Top and bottom first.

The kiln vent helps keep the air circulating inside the kiln which helps keep temps even from top to bottom ...
Having air moving outside really won't help as much.

I soak for twenty minutes then fire down to control the rate of cooling which helps as well.

My top and bottom are still about one half a cone cooler than the center so my firings are aimed at getting the cooler spots to the right temp.

I have also heard of potters adding a blanket of insulation to the lid to help keep the heat in.

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#3 GEP

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Posted 03 May 2010 - 12:02 PM

This is my strategy for addressing the same problem ... I keep the bottom shelf and the top shelf tall and loose. Minimum 6" tall, and I pack the pots with about 1" between them. The middle shelves can be shorter and packed as tightly as possible. The extra density in the middle takes more energy to heat up, therefore slows it down.

If you don't have an undermounted vent, then you should always have at least one peep open. Not for evening out the heat, but for allowing the corrosive gasses to escape. If those gasses are trapped inside, this will shorten the life of your elements.

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#4 hansen

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Posted 03 May 2010 - 04:35 PM

Clay Lover: My kiln is quite a bit different from yours but I have some of the same issues. I have a 2 section L&L 18" with Dawson Kiln Setter. During a typical cone 9 firing I keep the peeps out until the temp gets to cherry red, then the bottom one goes in an hour or two before the top one. I keep the bottom hotter than the top, use your judgement and past experience. It depends on how you load, and where the elements are in relation to the shelves. Ideally you have elements centered where the pots are - again you have to use your judgement. I don't put both top and bottom circuits on full until the last hour or so. Cone 9 is going to take about 11 hours this way. If you use a kiln vent system, expect the bottom to start getting hotter than the top, the reverse problem. I try to get the bottom heated up first, this seems to help.
h a n s e n

I would appreciate some suggestions from more experienced potters on this.

I have a new Scutt 1027 Kilnmaster, hope it is OK to mention brands. I haven't been able to adjust things to get it to have cones even from top to bottom. I am new to firing at home and working my way through this. So far, I have fired with all peeps in and gotton a full cone cooler on the top shelf, with resulting glazes under developed. I put the cones in the same place each time and leave 2" above and below the themocouple with shelves. I use the Corelite shelving.

Next firing I took out the top peep at the suggestion of the Skutt tec guy, got the same looking cones, but that time the bottom was a full cone cooler, like I flipped the temps from top to bottem. Skutt guy said to slow down the last climb, I had set it for 200* per hour to 2195 with a 10 minute hold. He said that was too fast to get even temps through out.

Last night I unloaded a kiln that I has increased the peak soak from 10 minutes to 15 minutes and with a slower, 125* climb to peak, which I set at 22200*. I kept the peeps all in. The cones look more consistent, but I didn't have a top shelf, the only shelf was at mid way, with a full shelf of tall slender pieces with tall handles, so not real dense at the top.

I should add, I don't have a vent, the kiln is outside of my studio in a covered shed. the breeze blows through. The Skutt rep says I won't get even without having peeps out, but when I took them out, nothing improved, only reversed the cool area from top to bottom.
Any advice or similar experiences, I would love to hear. Thanks in advance!


h a n s e n
Stone House Studio, Alexandria, Virginia

americanpotter.blogspot.com
thesuddenschool.blogspot.com

#5 clay lover

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Posted 03 May 2010 - 08:12 PM

Chris, I increased the peak temp 5* and increased the hold from 10 to 15 min. Seemed better, if I increase the hold to 20 minutes, do I need to lower the peak temp?

I am doing a controlled down fire, ramp 4 is a drop from 2200 to 1900 and a hold of 30 min at 1900. Then down 125* and hour to 1750, no hold and off. The kiln cooled to 200* to be opened in 13 hours from the 2200 peak.
I didn't have any matt glazes in this firing, so don't know how that will work with these settings.

#6 Kristen

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Posted 03 May 2010 - 11:07 PM

i have just ordered the same kiln and mine is going to be in a garage without a vent so all this info is great! I was wondering, did you get the 2 inch or 3 inch brick?

#7 clay lover

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Posted 04 May 2010 - 08:34 AM

Kristen, I got the 2", I guess the 3" might have been better, but I talked to Bracker's where I got it and they said it wouldn't make any diff in the performance of the kiln, now I'm wondering if I should get a vent. John Hesselberth said I should get no more than 1/4 cone diff between shelves, that's after I figure all this oout.

I want to know more about how taking out peeps should help even it up.

#8 Chris Campbell

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Posted 04 May 2010 - 10:16 AM

I hope your garage is not attached to your house if you are not going to vent it.
You really do not want those fumes traveling through your home.
Opening the garage door often just makes it worse as the wind blows in .... Not out!

As to the temp ... I usually go by how full my kiln is and how critical the final temp is.
I confess that I do not use any glazes that are thar fussy so someone else would be a better
judge of that.

Chris Campbell
Contemporary Fine Colored Porcelain
www.ccpottery.com

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#9 Brenda Neall

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Posted 13 May 2010 - 11:23 AM

After reading the posts for this, I gotta tell you how much I love my Cone Art Kiln and Bartlett controller. I purchased a 2327D in 2008. It comes standard with 3 zone control (thermo couplers placed in the top, middle and bottom sections). The biggest bonus is the ability to use the Bartlett controller settings to adjust the thermo couplers to register higher or lower overall by cone or more important, different in each zone if your firings are uneven between top and bottom.

#10 hansen

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Posted 13 May 2010 - 04:15 PM

I hope your garage is not attached to your house if you are not going to vent it.
You really do not want those fumes traveling through your home.
Opening the garage door often just makes it worse as the wind blows in .... Not out!

As to the temp ... I usually go by how full my kiln is and how critical the final temp is.
I confess that I do not use any glazes that are thar fussy so someone else would be a better
judge of that.


h a n s e n
Stone House Studio, Alexandria, Virginia

americanpotter.blogspot.com
thesuddenschool.blogspot.com

#11 hansen

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Posted 13 May 2010 - 04:22 PM

I have to concur with Chris - although some glazes are very fussy about a one cone difference, such glazes typically come out different each time anyway. If you are looking at production concerns for wholesale or even production retail you'll want liner glazes with very broad ranges, and for your speciality glazes, again, broader firing ranges. There are about 4-5 ways to make the ranges broader. One glaze I use is called "cone 4-14" for example, so whether it fires to cone 6 or cone 8, you can't tell the difference. You think you have problems? Some of these people with their newly constructed anagamas might have cone 12 in the front and cone 4 in the back. You have to make adjustments for all kinds of thing.
h a n s e n
p.s. down draft gas or wood are the most even temp kilns, IMHO


I hope your garage is not attached to your house if you are not going to vent it.
You really do not want those fumes traveling through your home.
Opening the garage door often just makes it worse as the wind blows in .... Not out!

As to the temp ... I usually go by how full my kiln is and how critical the final temp is.
I confess that I do not use any glazes that are thar fussy so someone else would be a better
judge of that.


h a n s e n
Stone House Studio, Alexandria, Virginia

americanpotter.blogspot.com
thesuddenschool.blogspot.com

#12 clay lover

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Posted 22 May 2010 - 09:17 AM

I have to concur with Chris - although some glazes are very fussy about a one cone difference, such glazes typically come out different each time anyway. If you are looking at production concerns for wholesale or even production retail you'll want liner glazes with very broad ranges, and for your speciality glazes, again, broader firing ranges. There are about 4-5 ways to make the ranges broader. One glaze I use is called "cone 4-14" for example, so whether it fires to cone 6 or cone 8, you can't tell the difference. You think you have problems? Some of these people with their newly constructed anagamas might have cone 12 in the front and cone 4 in the back. You have to make adjustments for all kinds of thing.
h a n s e n
p.s. down draft gas or wood are the most even temp kilns, IMHO



I hope your garage is not attached to your house if you are not going to vent it.
You really do not want those fumes traveling through your home.
Opening the garage door often just makes it worse as the wind blows in .... Not out!

As to the temp ... I usually go by how full my kiln is and how critical the final temp is.
I confess that I do not use any glazes that are thar fussy so someone else would be a better
judge of that.



#13 clay lover

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Posted 22 May 2010 - 09:18 AM

Hanson, I would be very interested in knowing some of the "4-5 ways to extend the firing range of a glaze," that you mentioned. Are you willing to instruct?

#14 hansen

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Posted 23 May 2010 - 02:20 AM

Hanson, I would be very interested in knowing some of the "4-5 ways to extend the firing range of a glaze," that you mentioned. Are you willing to instruct?


I'm just another potter who has struggled with some of the the same things. So I was looking into the basic textbooks for answers.


"If you are looking at production concerns for wholesale or even production retail you'll want liner glazes with very broad ranges, and for your speciality glazes, again, broader firing ranges. There are about 4-5 ways to make the ranges broader. One glaze I use is called "cone 4-14" for example, so whether it fires to cone 6 or cone 8, you can't tell the difference."


This glaze is called Schwieger's Liner and it is said to be workable from cone 4 to cone 14. I haven't tested this theory, but I looks the same at cone 6 as it does cone 8.
50 Plastic Vitrox
50 gerstley borate
(I substituted Laguna borate)
you can add 10-15% zircopax to make it whiter


This example has a broader firing range because of the use of the element boron.


Lithium as opposed to potassium or sodium gives a broader range, according to the text books.


Zinc oxide will broaden the range.


Magnesium broadens the range.


Use of the mineral feldspar broadens the range.


A combination of minerals which proportionally reflect the ratio called a "eutectic" will lower the melting point and will have the broadest range within a system of similar glazes. However, this really only applies where minerals which are chemically combined are combined in similar ways. In other words, although scientifically we can demonstrate that a frit, which has already been fired and chemically combined, is reground, and if another frit which has been fired the same way and reground the same way, the one closest to the eutectic point will be the both the most fusible and have the lowest melting point.


All this seems kind of abstract, however these are rules of thumb whether you are scratch formulating glazes all the way from Unity to batch, or if you are simply reading recipes online. It is easier to grasp looking at the history of ceramic glaze development. For example, the use of feldspar or porcelain stone was one of the first strides forward into high fire development in China, and an improvement over the mostly wood ash, limestone ash, and clay mixtures which are the basis for earliest glazes. It melts to form a glaze but maintains viscosity through a wider range of temperatures. Wood ash glazes will go from a stable matt glaze to a shiny runny glaze within a fairly narrow window. Hence, feldspar was deemed useful because it was more controlable and predictable.


Zinc glazes were developed in the 19th Century in the USA mostly for oxidation fire in the mid-range. It was added to the basic feldspar, whiting, clay, and flint high fire mixtures mentioned above because it both lowered the melting point but also was more predictable and stable.


Magnesium has it's greatest value when used in reduction high fire studio potter glazes from the '60's and '70's. It can produce a buttery satin matte. In a similar way, it helps get more predicability in the kiln


Eutectic glazes are mostly the concern of the scientist and the laboratory, but back in the day when leaded frits were common, the best ones were generally those in the eutectic. Lead, Silica, and Alumina in different proportions have several different eutectic points at several different cones.


Boron is a strange case because it acts as a refractory at low temperatures, acts as a glass-former, but also has fluxing strength.


So, in applying this to mid-fire electric I would say look for glazes with feldspathic minerals, and/or zinc oxide, and/or boron


does this help?


h a n s e n



h a n s e n
Stone House Studio, Alexandria, Virginia

americanpotter.blogspot.com
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