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Resilience Of 06, Recommendations?


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#1 two-fires

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Posted 07 February 2014 - 04:39 PM

Howdy all,

 

I've got a rookie question here. I've only handled cone 6-10 clays and glazes, and I have a friend that wants a particular low-fire glaze on some items... So...

 

Does anyone have an estimate (or specific number, why not) for how resilient a cone 06 clay is, compared to a cone 10, all things else being equal?  To standardize a bit, let's say it's a 1cm thick slab, slump-molded as a bowl. 

 

As for "resilience," I guess I'd consider how well it held up to everyday use as a general, inaccurate metric. But I assume there are more specific, scientific ones...? 

 

Also, can anyone recommend a white low-fire clay body that handles larger, slab-building projects well? I suppose a sculpture clay would be fine.

 

Many thanks for any help here. 



#2 Norm Stuart

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Posted 07 February 2014 - 05:17 PM

Feel confident using a Cone 6 clay in both Cone 6 glaze firings and or a Cone 06 glaze firing.  Ware made of a Cone 6 clay bisque-fired to Cone 04 and glaze fired to Cone 06 will almost always be stronger than a "Cone 06 Clay" fired to Cone 06 - even if it is glazed and refired again to Cone 06.

 

Most Cone 06 earthenware clays are very porous. They're designed for making a different type of ware rather than being designed for Cone 06 glazes.  If you are trying to make an unglazed Kimchi fermentation jar, this is the clay you're looking for.

 

I question whether some Cone 06 clay bodies, those consisting of a high percentage of Talc, serve any useful purpose today.  These High-Talc Cone 06 clays will melt into a glaze all over the kiln at Cone 6, yet they look indistinguishable from Cone 6 clays.

 

For this reason alone, if you want to use the brighter color palette of Cone 06 glazes, feel confident using them on Cone 6 clays, either after the clay is bisque-fired to Cone 04, or after the clay has been glaze fired to Cone 6.

 

I use both Cone 6 and Cone 06 glazes on the same pieces, sometimes with an additional Cone 016 gilding firing.

 

After glaze firing to Cone 6 and before glaze firing at Cone 06 - I have applied Cone 6 glazes, to become a very matte covering, as well as Cone 06 glazes over the fired Cone 6 glazes which have enough flux to not only melt during the Cone 06 firing, but also slightly melt-into the Cone 6 glaze and bind with it.

 

Howdy all,

 

I've got a rookie question here. I've only handled cone 6-10 clays and glazes, and I have a friend that wants a particular low-fire glaze on some items... So...

 

Does anyone have an estimate (or specific number, why not) for how resilient a cone 06 clay is, compared to a cone 10, all things else being equal?  To standardize a bit, let's say it's a 1cm thick slab, slump-molded as a bowl. 

 

As for "resilience," I guess I'd consider how well it held up to everyday use as a general, inaccurate metric. But I assume there are more specific, scientific ones...? 

 

Also, can anyone recommend a white low-fire clay body that handles larger, slab-building projects well? I suppose a sculpture clay would be fine.

 

Many thanks for any help here. 



#3 Mark C.

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Posted 07 February 2014 - 05:17 PM

For me cone 06 wares are vey fragile and do not hold up to everyday use -cone 6 yes cone 10 yes but 06 snaps like toast-at least thats what I have noticed.

As far as display pieces its just fine.

Mark


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#4 Pres

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Posted 07 February 2014 - 07:28 PM

For me the problem with ^O6 ware even if using ^6 clay would be absorption. For this reason, your ware should be glazed completely, and stilted-one of the reasons I got out of ^06 in the HS where I taught.  A ^6 clay may be stronger even if bisqued at a higher temp and then glazed for ^06, but it would not be vitrified as it would be in a ^6 glaze firing.


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#5 Bob Coyle

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Posted 07 February 2014 - 08:32 PM

Cone 6 is to use... cone 06 is to look at. Any other use and you might have trouble. as noted by Norm, Mark and Pres.



#6 bciskepottery

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Posted 07 February 2014 - 09:55 PM

Attached File  S1987_99.jpg   37.81KB   0 downloads

Three thousand years from now, I hope I'm as resilient as this earthenware vessel, made between 1000 and 600 BCE, in the Mesopotamia area. Of course, the only way that will happen is if someone takes my ashes and makes them into a glaze. This vessel is from the Smithsonian's Freer collection.

Earthenware vessels can be used for every day functional ware. Most folks working at that temperature bisque fire higher than glaze firing, mostly to prevent glaze defects caused by outgassing by the clay body. So, bisque to cone 04, glaze to cones 05, 06. Absorption is an issue; earthenware does not vitrify at low temperatures; however, many potters working with earthenware apply terra sigilata to unglazed areas to help seal the clay and improve absorption. Or, they glaze the entire piece and place it on stilts for firing, then grind down any glaze points that occur.

White low fire clays, often made with talc, are not earthenware clays; earthenware clays are red. White low fire clays are manufactured to for low firing temperatures. Most have even higher absorption rates than earthenware. Majolica and similar techniques were developed to give a white look to earthenware -- imitation porcelain.

As with any clay body and firing temperature, there are advantages and disadvantages. Yes, earthenware is more porous; but, that same porosity makes it a better insulator. Heat water (or tea, coffee) in a porcelain, stoneware, and earthenware mug in the microwave . . . which one will you burn your hands on? With proper design and construction, earthenware can be as functional as you want it to be. You just have to learn how to compensate for its strengths and weaknesses.

#7 Pres

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Posted 08 February 2014 - 01:16 AM

Earthenware does vitrify at 06 or near about, whereas the mid range would only vitrify at 6. So there would be more of an issue here I think than if he were to use a true earthenware clay.


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#8 Norm Stuart

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Posted 08 February 2014 - 02:04 AM

If you use an Earthenware clay with a wide firing range, there's nothing wrong with using Earthenware.

 

As our Pres pointed out in December 7, 2011 you don't want to take a chance firing Cone 06 clays to Cone 6 unless your vendor tells you this is definitely an unfluxed Earthenware which won't melt at Cone 6.  It's a real problem introducing these clays into a studio which also fires to Cone 6.   http://community.cer...-vs-6-question/

 

The bottom line is, if someone likes the brighter colors of Cone 06 glazes, the ware will be stronger if it's made from stoneware not fully densified at Cone 04 than earthenware "densified" to the extent this porous type of clay actually densifies at Cone 06 or Cone 04.

 

On the Antiques Roadshow there's a very good reason why antique majolica ware in good condition is valued at such high prices -- because most antique earthenware majolica has spalled-off large portions of the glaze or has experienced mechanical damage as Earthenware is soft and porous, even when fired to the correct cone.

 

It used to be customary to refer to ware as vitrified when it was fired to the correct cone.  But ceramic scientists, like John Hesselberth, have since pointed out that the actual mechanism in non-porcelain clays is densification as stoneware and earthenware clays never actually vitrify into a glass even when fired to Cone 10.

 

Below is a photo of a Cone 06 Earthenware bowl my partner threw and fired to Cone 10 a number of years ago.  You can definitely see where the form has sagged at this high firing, yet tap it and you can hear it has still not been fully densified, although it's far more densified than it would have been at Cone 06.  Earthenware clays categorized as Cone 06 are fine, if you have taken the step of asking your clay vendor for a Cone 06 earthenware body which is kiln safe if fired to Cone 6 or the top cone your studio fires to.  In this case careful selection of an Earthenware body with a firing range up to Cone 10 made this safe, if somewhat saggy.

 

Choose a Cone 06 clay with a high percentage of talc or similar in the clay body and you have serious damage to your kiln rather than this artistically sagged fruit bowl.

med_gallery_18533_680_21583.jpg

 

attachicon.gifS1987_99.jpg

Three thousand years from now, I hope I'm as resilient as this earthenware vessel, made between 1000 and 600 BCE, in the Mesopotamia area. Of course, the only way that will happen is if someone takes my ashes and makes them into a glaze. This vessel is from the Smithsonian's Freer collection.

Earthenware vessels can be used for every day functional ware. Most folks working at that temperature bisque fire higher than glaze firing, mostly to prevent glaze defects caused by outgassing by the clay body. So, bisque to cone 04, glaze to cones 05, 06. Absorption is an issue; earthenware does not vitrify at low temperatures; however, many potters working with earthenware apply terra sigilata to unglazed areas to help seal the clay and improve absorption. Or, they glaze the entire piece and place it on stilts for firing, then grind down any glaze points that occur.

White low fire clays, often made with talc, are not earthenware clays; earthenware clays are red. White low fire clays are manufactured to for low firing temperatures. Most have even higher absorption rates than earthenware. Majolica and similar techniques were developed to give a white look to earthenware -- imitation porcelain.

As with any clay body and firing temperature, there are advantages and disadvantages. Yes, earthenware is more porous; but, that same porosity makes it a better insulator. Heat water (or tea, coffee) in a porcelain, stoneware, and earthenware mug in the microwave . . . which one will you burn your hands on? With proper design and construction, earthenware can be as functional as you want it to be. You just have to learn how to compensate for its strengths and weaknesses.



#9 bciskepottery

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Posted 08 February 2014 - 09:33 AM

Getting back on track, the original post asked about working with a low-fire glaze and for suggestions on a white low fire clay body. I don't think the question was regarding using low-fire glaze on a high-fire clay body.

I believe if you use a low-fire glaze on a high fire clay body, even at bisque temperatures, you are more likely to run into issues of glaze fit (crazing or shivering) due to inconsistencies between the COE of the glaze and clay. Not absolute, but more likely. You could luck out. As for durability, you'd want to test to make sure if there was good fit especially if the items are functional.

If you use low-fire clay with low-fire glazes, the likelihood of such issues are reduced, but not necessarily eliminated.

I've only used earthenware -- the red stuff; no experience with white low fire clays. So, I can't help out there. Some white low fires use a lot of talc. So, maybe the best advice on clay body is to work with your clay supplier and manufacturer -- if talc is not something you want, ask for a body with no or less talc.

Here are two links that may be helpful. The first is Linda Arbuckle's handout on earthenware clays. The second is a discussion threat from the Clayart archives that discusses Pete Pinnell's findings on clay strength -- a report based on work done by his students that found earthenware to be . . . well, I'll just let you read it and be surprised. That report/article generated a lot of discussion -- including on CAD (search for previous threads).

http://lindaarbuckle...earthenware.pdf

http://www.potters.o...ubject87702.htm

#10 Karen B

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Posted 08 February 2014 - 12:27 PM

This is the low fire white earthenware that I use:  10VW Very White Earthenware ^05 Laguna

 

I have some small bowls I made from this clay about 7 yrs ago that I kept for my family and use frequently and put in the 

dishwasher. Also have even older terra cotta bowls that we use all the time with no problem. What I don't

like to make from earthenware is teapots or too thin mugs which will burst when boiling water is added.

 

Karen     Attached File  vwlofirebowl1.jpg   78.34KB   1 downloads



#11 NancyAmores

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Posted 08 February 2014 - 12:31 PM

I've dropped pendants made of low fired earthenware on the concrete floor and watched them bounce around before landing without a chip. Did the same with stoneware, shattered like a plate. For small non-functional wares, earthenware is exceptional. It's a cinch to work, is lighter and so can be larger, and costs nearly nothing to fire. But I always feel as though I have to defend my decision to work with it, easy to get pigeonholed as a 'paint bar' artist, so I've been moving to stoneware. It's a shame because terra cotta really is a beautiful clay that gets a bad rep.



#12 neilestrick

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Posted 08 February 2014 - 12:48 PM

In my experience, low fire glaze have fit issues when applied to cone 6 or cone 10 clays. Occasionally I have seen it work, but typically they craze badly, or shiver, and just never stop pinging.

 

Most commercial earthenware clay bodies will not have a firing range beyond cone 1 or so. Most commercial terra cotta clays are simply Redart and ball clay, and most commercial white earthenware bodies are talc based. There are some calcium based white bodies, but they won't fire any hotter. All will melt into puddles if fired to cone 6. I've replaced several kilns where the entire load was puddled. If a clay body can be fired to cone 6 or 10, I'm not sure how it can be considered earthenware. If it sags at 10 but doesn't melt, it's probably just a high iron cone 6 body.

 

The primary issue with low fire, porous bodies is the porosity. The glaze is the only thing making the pot water tight. So as soon as the glaze crazes, which it will at some point, hopefully no time soon, liquids can seep into the walls of the pot, and weep out, causing damage to furniture. Also, once liquids seep in, it can be very difficult, even impossible, to get them out. I have seen mold growing underneath the glaze on low fire pots.

 

As the Pete Pinnell article that Norm posted above shows, in that particular type of test that they did, the earthenware is stronger. Is it stronger in daily use, maybe maybe not. The type of impacts that pots suffer in daily use can be quite different than the test they ran. In my experience the low fire pots are not as durable. As Mark noted, I too have never been able to snap apart a cone 6 pot like low fire pots.


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#13 Norm Stuart

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Posted 08 February 2014 - 12:50 PM

What does Laguna Clay say is the top firing range on 10VW ^05 clay?

 

This is the low fire white earthenware that I use:  10VW Very White Earthenware ^05 Laguna

 

I have some small bowls I made from this clay about 7 yrs ago that I kept for my family and use frequently and put in the 

dishwasher. Also have even older terra cotta bowls that we use all the time with no problem. What I don't

like to make from earthenware is teapots or too thin mugs which will burst when boiling water is added.

 

Karen     attachicon.gifvwlofirebowl1.jpg



#14 Karen B

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Posted 08 February 2014 - 02:49 PM

 

What does Laguna Clay say is the top firing range on 10VW ^05 clay?

 

This is the low fire white earthenware that I use:  10VW Very White Earthenware ^05 Laguna

 

I have some small bowls I made from this clay about 7 yrs ago that I kept for my family and use frequently and put in the 

dishwasher. Also have even older terra cotta bowls that we use all the time with no problem. What I don't

like to make from earthenware is teapots or too thin mugs which will burst when boiling water is added.

 

Karen     attachicon.gifvwlofirebowl1.jpg

 

 

 

Says 06 to 3.  But even so, they give the shrinkage rate at cone 4 (11.2%). 



#15 Norm Stuart

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Posted 08 February 2014 - 03:36 PM

So Laguna 10VW Cone 06 clay is the sort of Cone 06 clay which is perfectly safe to use in a Cone 6 studio.  A brilliant choice on your part.

 

Cone 06 glazes will work on this clay just as well as they work on Cone 6 clays.  You may try applying Cone 5/6 glazes to your clay and firing to Cone 5 or 6.  You may encounter minor problems, but it won't endanger your kiln.

 

I think wonderful things can be done combining high fire and low fire glazes.  Our studio has a book of beautiful pieces which have combinations of glazes from various cones - some of the pieces with the most incredible depth of glaze were fired as many as 16 times.

 

Our studio purchased a Cone 2 porcelain which Laguna offered briefly.  It had a firing range up to Cone 4.  The downside of firing this clay outside of its range to Cone 6 proved to be bloat.  What this means is the clay was partially decomposing into gas, and this gas became trapped inside the clay body so it puffed-up like a puff-pastry.  This sort of problem poses no danger to our kiln, even it annoyed the artist who make the piece and wanted to fire at Cone 6.  That's the sort of problem you may encounter with firing your Cone 05 clay to Cone 6, or it may simply slump a little.

 

The Laguna Cone 06 earthenware my partner used on the partially slumped fruit bowl had a firing range up to Cone 5 - at which point it retains it shape.  But glazed with a Cone 10 glaze and fired to Cone 10 in a gas kiln this Cone 05 earthenware slumped and deformed a little in what I find to be artistic and pleasant manner.

 

Below is a photo of an even more wild experiment.  

I made a structure out of Laguna WC-953 Cone 10 paper-clay http://www.lagunacla...stern/wc953.php,

I then covered this ware with several thick layers of slip made from Laguna WC-437 Cone 6 Frost Porcelain

http://www.lagunacla...stern/wc437.php.

 

Looking at the specs, the shrinkage of the porcelain clay is 11% at Cone 5 while the shrinkage of the paper clay is only 8%, so I was hoping the porcelain slip would adhere fully to the paper clay, but crack in an artistic manner - and this is what happened initially in the bisque and more at Cone 6, just not as many cracks as I hoped. 

 

I applied several Cone 6 glazes and also a thin layer of the yellow Cone 06 glaze to this Cone 6 clay and fired to Cone 6.  I then applied additional layers of Cone 06 glazes and fired again at Cone 06.  The glaze covered the sharper edges of the porcelain clay shrinkage cracks which developed in the Cone 6 firing, as compared with the not sharp fractures which occurred at bisque.

 

 

What does Laguna Clay say is the top firing range on 10VW ^05 clay?

 

Laguna 10VW Cone 06 clay says its firing range is 06 to 3.  But even so, they give the shrinkage rate at cone 4 (11.2%). 

 

med_gallery_18533_691_991735.jpg

 

These are some other pieces made of a Cone 6 clay decorated with Cone 6 and Cone 06 glazes.

sml_gallery_18533_691_478219.jpg

 

This piece also includes Cone 6 glazes fired to Cone 06 - such as the white band around the neck.

sml_gallery_18533_691_487609.jpg

 

med_gallery_18533_691_230655.jpg

 

sml_gallery_18533_691_634423.jpg

 

 

You're going to enjoy combining Cone 6 glaze firings with Cone 06 glaze firings.



#16 bciskepottery

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Posted 08 February 2014 - 04:27 PM

I've been doing this for years.  I can see that Microsoft is not the only one who sells FUD, fear uncertainty, doubt.


While we can disagree and hold our own personal views as to what works for us, there should be no room in these forums for personal attacks or to characterize advice and suggestions as FUD. I would invite you to review the postings either I or Neil have made and find one where either of us have engaged in fear, uncertainty, or doubt.

#17 bciskepottery

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Posted 08 February 2014 - 05:07 PM

Must be the weather, but this forum no longer makes sense to me.

Ciao.

#18 two-fires

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Posted 08 February 2014 - 05:34 PM

Excellent. Thank you all for this discussion, all of which gives me more options than I knew I had.  Thanks for the direct recommendations responding to my initial post, and thanks also to Norm for getting at one heart of the matter -- I'm looking for whatever clay body will best fit my application. In this instance, it's whatever clay (of whatever firing range) will come out strong(est) yet glazes well with low-fire glazes. It seems that a cone 6 clay *may* work well -- and I'll go try some experiments down that route first, before committing the whole project. Thanks also to ya'll who explained the problems you had with those combinations.  I'll be wary, but optimistic.

 

This also prompted me to remember using cone 10 glazes in cone 06 firings -- yes, matte, bubbly, awesome textures. I remember "Hi-Ho Silver" came out really cool that way.

 

Also, kinda similar situation, here's two marbled cone 10 clays that were bisqued to 1200, then glazed with a cone 06 glaze, fired at 06--

http://www.arikiart....ze-path-lrg.htm

[abashed disclaimer -- years-old stuff of mine on that site, very green]

It came out quite fragile, almost "crumbly" on the sharp corners.

 

The shape of the "bowl" above is kinda what I'll be doing for my friend, so it heartens me that I may be able to use a cone 6 clay fired to low-fire glaze temp, and still have functional pieces. As you can imagine, that shape doesn't hold so well, and it's the precision of the sharp angles that makes it appealing... maybe.

 

Thanks again. Even more feedback would be great to have.



#19 Mark C.

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Posted 08 February 2014 - 06:29 PM

Heres a low fire story-about 20 years maybe 25 I was doing a show and the artist next to me was a low fire grapic ceramist.

She really wanted to trade so I did. I traded for this platter (15 inch) a few bowls and mugs with the chili peper theme.

Now I use my pottery-I also know how to handle it well . It goes thru the dishwasher or hand washed whatever. So today (25 years later) I looked around and all that is left of the less than Mesopotamia area age pottery is this platter I hung on the wall behind my stove. The rest died long ago.

If I had buried it in the dirt or under Saint Hellens ash in Oregon it may still be alive but for daily use its toast-except for the wall piece.

Thats my experience-others may vary 

Mark

 


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#20 Babs

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Posted 09 February 2014 - 01:26 AM

 

If you use an Earthenware clay with a wide firing range, there's nothing wrong with using Earthenware.

 

Wide firing Earthenware.......  Oxymoron.

A friend gave me a pitcher glazed with a high firing glaze which she assured me would be Ok in my firing range, I did not read the bag... Presumed it wa an iron enriched high firing clay.

Result:

Folded melted pitcher all over my shelf and nearby work.

Take the risk if you're a risk taker, otherwise read the bag and act accordingly.

 

Earthenware will melt before it fully vitrifies.

As Pres says above,

C06 will work on your C6 clay,prob won't fit the body,  but the pot will be less vitrified than putting it on earhtenware clay fired as the manufacturer advises. and so will be weaker.

SO what you asked in the primary instance, My advice, go buy a bag of low fired clay, make the stuff, fire and glaze accordingly. 






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