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Electric Vs Gas Firing - Surface Look - Clothes Or Skin


preeta

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is there a difference in look of how the glaze sits on the pot depending on the type and source of the heat.

 

i've done ^5 electric and ^6 gas (reduction) firing  (both at school) AND ^10 natural gas reduction firing at a professional potters studio.

 

and there is a difference in how the glaze sits on the pot - i feel.

 

^5 electric the glaze looks like clothes on a person. like a winter coat. 

 

^6 natural gas reduction fire - like a leotard. no glaze made specifically for reduction. use the usual ^5 glazes and see how they act on reduction. 

 

but ^10 reduction firing the glaze felt more like a part of the pot. not like clothes. but actually skin as if part of the pot. 

 

i dont know how else to describe it. ^10 felt such a part of the pot. ^5 and ^6 felt it was put on the pot. its not about colour. its more about the feel and how the surface of the pot feels. 

 

why is it that way? is it because of the glaze application or are there subtle differences due to the type of firing. 

 

and it wasnt just me. when i took my pots in to show my advanced potter friends in school as they held the ^10 pots they immediately noticed it felt different and they struggled to express how much part of the pot the surface felt. 

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I ThInk that is more dependent on the combination of clay, glaze and firing rather than atmosphere. Firing down in oxidation certainly enriches the surfaces on certain glazes. SO in my opinion i would say no. BUt often fast auto firings with commercial glazes I would say yes.

I know the look you are talking about.

Marcia

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Are you working with stoneware? In reduction you'll get iron spots coming through, which gives a visual blend between the clay and the glaze, but a good speckled cone 6 stoneware will give you a similar effect. The foot of the pot is always a giveaway, though, as reduced stoneware bodies definitely have a different look than oxidized bodies. When working with white bodies, however, it's much more difficult to tell the difference between reduced and oxidized bodies, and they have much less effect on the look of the glaze. It's often impossible to tell how white bodies were fired. If you don't like how the cone 6 glazes look in oxidation, I would try a darker clay body. It could simply be that you're not getting the color of the clay coming through as much as in reduction. If you're using the same clay body for both, then that's definitely the case. Iron is more active in reduction, so you need more of it in oxidation to get a similar effect. You can't just use the same materials for both and expect similar results. Each type of firing requires specific materials to achieve the desired results.

 

There are a lot of bad cone 6 glazes out there that look plastic-y, including a good percentage of commercial glazes. In my experience this comes from using too much boron in the formula. In the past, when cone 6 was considered the realm of hobby potters, Gerstley Borate was relied upon much too heavily, making high boron glazes. However a lot of great research has been done on cone 6 in the past decade, and there are a lot of really great glaze recipes out there now. Cone 10 glazes rely heavily on feldspars, which look and feel different than glazes that rely heavily on boron. But feldspars can also be used in cone 6 glazes. I've got many cone 6 glazes that contain no boron, and they are totally indistinguishable from cone 10 glazes.

 

I work in cone 6 oxidation, and people are always surprised that my work isn't cone 10 reduction. There's really very little you can achieve in a gas kiln that you can't do in an electric. You just have to learn about what's causing the results in each type of firing. I recommend taking a glaze formulation course, then you can work on making your own glazes that will give you the results you want in each type of firing.

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Guest JBaymore

An aspect that maybe you are picking up on is what is known as the "interface layer".

 

At high fire temps, there is a melding of the glaze eating into the body and the body growing crystalline intrusions into the glaze.  As firing end point cone goes down, this aspect lessens.

 

So at say overglaze enamel temps....... it is very much like a layer of paint on wood.  At cone 10 range....... in the cross section of the piece... you can't tell exactly where glaze layer starts and clay body ends.

 

best,

 

..............john

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This past weekend, I surprised yet another gas firer when she asked, "this is all reduction fired right?" and I said "No it's all cone six electric."

 

Although I will respectfully disagree with Neil that borates are the problem with cone 5-6 glazes. I love gerstley borate. I think the problem is Zircopax. Makes such flat colored glazes yuck.

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This past weekend, I surprised yet another gas firer when she asked, "this is all reduction fired right?" and I said "No it's all cone six electric."

 

Although I will respectfully disagree with Neil that borates are the problem with cone 5-6 glazes. I love gerstley borate. I think the problem is Zircopax. Makes such flat colored glazes yuck.

 

I have no problem with boron in general- I use it in a lot of my glazes and it's a wonderful flux at cone 6. I just think that when it gets too high that it makes glazes look plastic.

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Guest JBaymore

 I just think that when it gets too high that it makes glazes look plastic.

 

Also boron glass is weaker than silica glass.

 

Get just the right proportion of boron and silica glasses... and it is VERY strong though.

 

best,

 

................john

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all the glazes used were not commercial glazes but recipes handed down. 

 

John That is the answer i was looking for. the interface layer. i have not seen any ^10 electric that i am aware of. would melding together apply in the ^10 electric too and so the surface would actually feel/look like skin rather that something sitting on top - similar to ^10 reduction? therefore does that make the surface stronger? meaning restaurant ware which takes a lot of beatings. i know here at the state university they went through a lot of ^10 testing (both wood and gas) to get the right combination for a particular restaurant a few years ago. and it has held up very well. 

 

if the body and glaze are one, could it mean they wont chip so easily? meaning is it melding that makes the surface stronger or is it the right combination of glass formers or bit of both?

 

is the melding happening to some degree at any temperature in the kiln and as it goes higher the line between glaze and body becomes more hazy? is it some degree of melding that makes the glaze stick instead of falling off?

 

neil yes i use stoneware. ^10 i used a buff body ^5 and ^6 i've used both white, buff and red clay body. i do plan to take a glaze class when i can find one i have access to. in the meantime i am reading a lot.

 

right now i am simply experimenting with the glazes we have at school. i've helped to mix a few (basically just follow the recipe). i am trying to understand them. why the red glaze in oxidation turns green in reduction and vice versa. i've been noting and observing quite a bit (esp since ^5 IS ^5 but ^6 is usually ^6 1/2 or ^7).

 

thanks for the boron and Zircopax discussion. i will keep a note of that. perhaps that might explain some of the yucky colour i achieved.

 

every time i have done ^6 reduction at school everyone has told me how much my pieces look like ^10 reduction. a couple of pieces this reduction ^6 firing i would have to agree too. on red claybody - my regular transparent brown (in a ^5 electric) came out looking just like a tenmoku in the ^6 reduction. 

 

i am still learning about why and how. and doing test pieces to test my theory. 

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Guest JBaymore

 

John That is the answer i was looking for. the interface layer. i have not seen any ^10 electric that i am aware of. would melding together apply in the ^10 electric too and so the surface would actually feel/look like skin rather that something sitting on top - similar to ^10 reduction?   YES   therefore does that make the surface stronger? YES  meaning restaurant ware which takes a lot of beatings. i know here at the state university they went through a lot of ^10 testing (both wood and gas) to get the right combination for a particular restaurant a few years ago. and it has held up very well. 

 

if the body and glaze are one, could it mean they wont chip so easily? YES   meaning is it melding that makes the surface stronger or is it the right combination of glass formers or bit of both? BOTH

 

is the melding happening to some degree at any temperature in the kiln and as it goes higher the line between glaze and body becomes more hazy? YES .... except at the lower ranges........ and this is an somewhat arbitrary point I'm drawing but maybe below cone 04...... not much interface  is it some degree of melding that makes the glaze stick instead of falling off? 

 

All of the above "yes's" also have the standard ceramic "it depends" aspect.  So those are broad generalities.

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Guest JBaymore

One big reason you don't see many folks firing cone 9-10 electric oxidation is that A.) it tends to kill standard type elements faster  B.) most "hobby type" (hex type) electic kilns are quite underinsulated and C.)  electric costs are high compared to gas costs (in part because of the poor insulation).

 

Better made electric kilns like the Fredrickson front loaders go to 9 nicely and rival a commercial gas kiln for insulation and cooling rates.  We have a Fredrickson front loader at the college (amongst a Skutt hex and an L+L square)... and some students do high fire electric oxidation in it.

 

best,

 

..............john

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thanks john.

 

i had learnt about elements from my very first ceramic class where the proff. was saving the elements of his skutt kiln and so wouldnt go higher than ^04. so the importance of elements was drilled to me from a professor who saved his job and a ceramic department by keeping his kiln going (this was a satellite little college where the dean would not allow even a raku kiln).

 

i just learnt about insulation when the lab tech walked me through the electric kilns we have (3 skutts and one bailey). our school never fires beyond ^5 in our electric kilns. 

 

nor do we as students ever get to fire our kilns - which is understandable.

 

and costs. yes. i imagine because we fire ^5 we are constantly firing. you can fire bisqueware and glazeware in a week - which is unheard of in the other community colleges whose turn around is usually two weeks or more. they fire ^9 or ^10 reduction.  

 

but i WILL have access when i volunteer with the local state university and will be allowed to fire after hours - a wood fire, soda and gas kiln. dont remember paying that much attention to the electric kilns there. 

 

i have seen old ^9 test tiles in a box hidden away and some glaze notes too. not sure if it was for electric or gas as we have 3 gas kilns (two alpines and a brand new Geil that has never been used yet) so i would imagine we did ^9 here too (just like the other community colleges in this district) but with this new proff. we now limit to ^5 for electric. with all the back issues i think a car electric kiln is in the new future. 

 

sadly no one really experiments with ^6 reduction glazes here. mostly students do oxides. mostly the sculpture students use the gas kilns with just a few who puts an errant functional ware in the gas kilns. 

 

at the professional potters it is i believe a Geil gas that has been taken to ^12 at times. 

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Guest JBaymore

 

When I was in school the teachers never fired the kilns. The students were responsible for all firings. It's an important part of the ceramic process, and should be learned.

 

 

Our undergrad majors are required as a specific part of the curriculum to learn to fire both electric and gas kilns.  One full 3 credit course is devoted to that aspect called "Kilns: Practicum".  They handle and process probably 90% of the department's overall production including the Community Education classes work.

 

best,

 

................john

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Neil when i was last at our local state univ, attending the visiting artist workshop, i met a bunch of kids who had come from many different community colleges around California.

 

i was blown away how different the policies are in all the community colleges (ccs). if i drive an hour or hour and half and attend a couple of community colleges i would have much more freedom to do things. make my own claybody, make my own glazes and fire my own kiln.

 

the philosophy where i am - the idea is if that can be done in a 4 year college then you cant do that in the community college. it takes 6 years for the art department to get new equipment so the proff. starts early (like a request for car kiln). 

 

sadly the ceramic department is the step child of our art department. while other tenured art teachers teach a minimum of 3 classes to get full pay our ceramic proff. has to teach 7 classes (3 of those classes are all in one class - wheel throwing - begin, interm, advanced) plus maintain office hours. 

 

however we are the lucky ones compared to the other ccs. other schools have 3 different begin wheel throwing classes and the others no wheel throwing (yet they have the most number of kilns and variety of types of firing that does not really get used). 

 

i wish things were different. but as a wanna be potter i am at the best place i could be in the city without driving an hour and half or two hours. at least i dont have to wait around for my experimentation of glaze ware. i can throw and experiment with glazes at the same time.  other students from other parts of the district drive to come to the cc i go to just so they could see the glaze outcome before they were ready to glaze another batch. 

 

since i show interest and due to my glaze testing i am also allowed to assist in the class. plus the glaze fire gets explained to me in detail as opposed to other students. i am taught here and there about our various kilns. plus if there are any wheels available you are allowed to throw during non throwing class time. the school does not know that. we are not allowed to be in the ceramic room if we dont have a class there. the proff. ignores that rule as a protest because two years ago they disallowed students repeating classes. 

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