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Differences in working with high fire and low fire clay


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#1 Knewcomb

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Posted 23 April 2012 - 07:24 PM

I've always worked with cone 6 porcelain just because that's what the community studio used. I bought a small kiln a few years ago but didn't know enough to get a computerized controller. I'm getting a new kiln and am debating if I really need one that goes up to cone ten or if a low fire (2000F) would suffice. So this time i'm asking before buying, what differences do you find working with low fire compared to high fire clays? I do sculpture as opposed to throwing.

#2 Mark C.

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Posted 23 April 2012 - 10:49 PM

I've always worked with cone 6 porcelain just because that's what the community studio used. I bought a small kiln a few years ago but didn't know enough to get a computerized controller. I'm getting a new kiln and am debating if I really need one that goes up to cone ten or if a low fire (2000F) would suffice. So this time i'm asking before buying, what differences do you find working with low fire compared to high fire clays? I do sculpture as opposed to throwing.


First as you are working with sculpture get the controller so you can fire slower cool longer.
As far as clays-out here in the west our high fire clay is cheaper-and throws better (I know throwing is not what you care about)
second its stronger than low fire clays-this may or may not matter to you???Are you shipping or moving the work around??
I used to fire sculpture for another artist and strength mattered so he used high fire clay and high fired it.He did not glaze the work.
Third in low fire you have about all the colors of a paint store in glazes which do not exist in high fire as the choices are more limited
Low fire has less selection of bodies for us out west compared to high.
Buy the way cone 6 is mid range not low fire as its hotter than 2000F
I answered your low fire questions but mid range is another slightly different story if thats what you meant?
Mark
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#3 Marcia Selsor

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Posted 24 April 2012 - 05:57 AM

If you are leaning towards sculpting in terra cotta, I think that is a good was to go. Firing sculpture to high fire in my opinion, seems unnecessary. The higher temperature can cause more warping and cracking. I'd look at maturity temperatures around ^2 or ^3 not ^04.
If you fire a terra cotta to maturity it is as strong as any clay fired to maturity. Look at Lisa naples work
http://www.bing.com/...les&FORM=RESTAB

She was giving a workshop and had a ceramics engineer in the group. The engineer explain that vitrification of the terra cotta clay body makes it as strong as stoneware.

Marcia

#4 Knewcomb

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Posted 24 April 2012 - 06:48 AM

Thanks for the responses,
I was considering cone six in the higher firing range since its above 2000f even though it's technically mid fire I wouldn't be able to use it with the lower temp kiln. I generally make small pieces of sculpture (about6-8 inches tall) or pendants for jewellery and do glaze them. I'm worried about strength in so far as I'm always afraid that things I've given people will break in everyday use. The one thing none of the courses I took ever covered was how to tell after firing if pieces were cured properly which is a big reason I want a controller.
Katherine

#5 Frederik-W

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Posted 24 April 2012 - 08:13 AM

I agree with Marcia.

High fire is a waste of energy. Be green. Don't waste.
Some people have an obsession about high firing.
Sculptural objects are for display, not functional use. It's not as if they are chucked in a kitchen sink every day.
If a sculptural ceramic object drops, it will break anyway, low or high fire.

Ceramics by nature is fragile. If people want unbreakable things, they can go get them in plastic or metal.
So do not fuss to much about things breaking.

I have worked with Terracotta and liked it a lot for sculptural things.


#6 Mark C.

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Posted 24 April 2012 - 10:08 AM

I also feel your mid range or lower temps is all you would need for that work. No need to go higher.
Mark
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www.liscomhillpottery.com

#7 OffCenter

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Posted 24 April 2012 - 12:31 PM


I've always worked with cone 6 porcelain just because that's what the community studio used. I bought a small kiln a few years ago but didn't know enough to get a computerized controller. I'm getting a new kiln and am debating if I really need one that goes up to cone ten or if a low fire (2000F) would suffice. So this time i'm asking before buying, what differences do you find working with low fire compared to high fire clays? I do sculpture as opposed to throwing.


First as you are working with sculpture get the controller so you can fire slower cool longer.
As far as clays-out here in the west our high fire clay is cheaper-and throws better (I know throwing is not what you care about)
second its stronger than low fire clays-this may or may not matter to you???Are you shipping or moving the work around??
I used to fire sculpture for another artist and strength mattered so he used high fire clay and high fired it.He did not glaze the work.
Third in low fire you have about all the colors of a paint store in glazes which do not exist in high fire as the choices are more limited
Low fire has less selection of bodies for us out west compared to high.
Buy the way cone 6 is mid range not low fire as its hotter than 2000F
I answered your low fire questions but mid range is another slightly different story if thats what you meant?
Mark


See similar thread about strength: http://ceramicartsda..._0&#entry15658. Strength depends on composition of clay and firing to maturity. My cone 13 pieces are fired to maturity and extremely strong but my earthenware fired to maturity is even stronger. Stoneware is NOT necessarily stronger than any other clay no matter what cone it matures at.

Jim
E pur si muove.

"But it does move," said Galileo under his breath.

#8 missholly

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Posted 24 April 2012 - 01:30 PM

i like to low fire because of the colors available and also i can bisque and glaze fire all in the same load.
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#9 OffCenter

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Posted 24 April 2012 - 03:10 PM

I've always worked with cone 6 porcelain just because that's what the community studio used. I bought a small kiln a few years ago but didn't know enough to get a computerized controller. I'm getting a new kiln and am debating if I really need one that goes up to cone ten or if a low fire (2000F) would suffice. So this time i'm asking before buying, what differences do you find working with low fire compared to high fire clays? I do sculpture as opposed to throwing.


another point: Grog and sand weaken clay. Often lots of grog is used in clay for sculpture. Once again the composition of the clay and firing to maturity is what is important, not temp. Almost any good clay would be strong enough for sculpture so why not go low fire and save time, energy, money, and wear on the kiln. Now, if you plan to put the sculpture outside then you have a whole new can of worms to deal with, but strength is a non-issue.

Potters are a stubborn. It doesn't matter what proof they are shown, there's still probably a majority who believe that trapped air causes pots to blow up and that stoneware is stronger than lower firing clays.

Jim
E pur si muove.

"But it does move," said Galileo under his breath.

#10 Walt

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Posted 24 April 2012 - 04:37 PM

If you're question is because you're looking at a kiln, I would suggest getting a high fire kiln simply
because it's more flexible.

You can always fire lower in it if you want, but if you get a low fire kiln, you'll never be able to high fire.
I think high fire kilns might also be more energy efficient and have better insulation.

As far as clay body, I think that's really a personal preference.
Vitrification temp is flux issue, and I don't think you can feel a flux when you're working a clay.
It kinda only matters when you're firing. Also, you can usually go past a rated temp pretty far
before it melts. Like.. you can fire alot of ^6 porcelain into 8-10ish, and also, since bisque is still
like..06, you could still use low fire glazes on a high fire body if the bisque strength is sufficient
for what you're making, and the contraction rates still work without crazing.

Anyway, a high fire kiln is alot more flexible. The only reason I can see getting a lower fire
kiln is if you'd have to have your electrical box replaced. In my older home, the electrical box
didn't carry enough electricity to run a high fire kiln, so I had to pay an electrician to put in a bigger
box, which added significantly to the overall cost of doing it. I had to think long and hard about that
since I could have run a mid-fire kiln without re-doing the electrical work.

Anyway, just something to think about. Hopefully you'll find it useful.

#11 Knewcomb

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Posted 24 April 2012 - 07:19 PM

Isn't money always the answer? I'm buying a new kiln and can only go up to 120v without running 175ft of heavy voltage wire and I can get a relatively larger low fire kiln compared to the high fire models. I was wondering more if people found major differences in working with the different temperature clays as well as any strength differences. And this probably quite a noob question but all the premade bisque ware that those pottery painting studios use are they actually low fire or are they also mid fires?
Katherine

#12 Marcia Selsor

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Posted 24 April 2012 - 09:41 PM

I use Chip Clausen's terra cotta recipe for outdoor sculpture in cold climates like Montana.
He tested it for 30 freeze/thaw cycles. He ran the Archie Bray Clay Business for decades. I have no problem with Terra Cotta with grog for outdoor sculptural or architectural work
Marcia

#13 OffCenter

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Posted 24 April 2012 - 11:54 PM

I use Chip Clausen's terra cotta recipe for outdoor sculpture in cold climates like Montana.
He tested it for 30 freeze/thaw cycles. He ran the Archie Bray Clay Business for decades. I have no problem with Terra Cotta with grog for outdoor sculptural or architectural work
Marcia


Did you glaze it? Have you tried other clays for outdoor sculpture/arch.?

Jim
E pur si muove.

"But it does move," said Galileo under his breath.

#14 Marcia Selsor

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Posted 25 April 2012 - 05:54 AM

I soda fired my terra cotta work with this clay body. Chip's is glazed. See his wall from his home.

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#15 OffCenter

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Posted 25 April 2012 - 08:20 AM

I soda fired my terra cotta work with this clay body. Chip's is glazed. See his wall from his home.


That's some wall! Thanks for the info.

Jim
E pur si muove.

"But it does move," said Galileo under his breath.

#16 Idaho Potter

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Posted 25 April 2012 - 04:12 PM

I also do a lot of sculpture and fire most of it to cone 6. I have a standard kiln-sitter kiln and an electronic control digital. I prefer the digital because of the ability of choosing a firing ramp--in bisque or glaze firing--that benefits the sculptures. Long and slow is much easier to attain when using a programmable kiln.

If you are happy with the clay you're using, why not continue on with it? Buying a kiln that will fire to cone 10 does not obligate you to fire to that temp. Fire your clay to its prescribed cone, and then you can glaze it in whatever glaze you want that is made for your clay's cone or lower. Vitrification gives you strength so once that is accomplished you have your choice of a wide spectrum of glazes from cone 06 (low fire) to cone 6 (mid-fire) and above to your clay's cone.

#17 Walt

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Posted 27 April 2012 - 03:45 PM

Isn't money always the answer? I'm buying a new kiln and can only go up to 120v without running 175ft of heavy voltage wire and I can get a relatively larger low fire kiln compared to the high fire models. I was wondering more if people found major differences in working with the different temperature clays as well as any strength differences. And this probably quite a noob question but all the premade bisque ware that those pottery painting studios use are they actually low fire or are they also mid fires?
Katherine


Money does seem to get you more.... but you can usually find a used higher temp kiln on craigslist.
Manual ones seem to find their way on there all the time, sometimes for pretty cheap.
If you can't do an electric hookup, you can always get a gas kiln, or convert a used kiln to gas.

If you go on youtube, and look at some of Simon Leach's videos, you can see how he converted a broken
electric kiln to gas with some inexpensive weed burners, which then changes your cost to gas burning. I
would suggest you do it outside though, mostly because carbon monoxide in reduction scares me. If you
haven't fired gas kilns though... that's probably not for you.

Another suggestion... if you're doing sculpture, you are probably not doing a high volume of work.
You might consider finding a pottery that will fire your pieces for you. Not a paint your own pottery,
but like... some place that teaches classes. They'll often fire your pieces in their kilns on a per piece
basis. The ones around me will also let you use their glazes for a pretty low fee, if you haven't gotten
into making your own glazes yet.




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