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Lucy

strength of earthen- vs stoneware

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Lucy    0

How much more strength re: shipping/handling would I get from making sculptures in stoneware vs earthenware?

 

Some of my earthenware work has appendages that I don't think can be packed safely for shipping. Would they be significantly stronger and less likely to break if I switched to a stoneware? (I love the earthenware I use and don't really want to get to know a new clay body but would consider if it paid off in ship-ability.)

 

thanks much,

Lucy

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neilestrick    1,381

Generally, stoneware is stronger since is fuses tighter. But when it comes to appendages that can snap, it may not make a significant difference. It may be worth running some tests.

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Mark C.    1,807

stoneware vs earthenware

If the question is both fired to cone 06 and both are fired to vitrification-meaning they both are 06 clays then I also say why bother very close and very weak.

As far as strength ^06 is very weak compared to higher temp clays

Even cone 6 clays do not hold a candle to cone 10 clays as far as strength especially cone 10 porcelains

Break some of each and you will see this to be true

Mark

PS as noted by Nelly packing does make a huge impact (no pun)

I always double box with at least 1 inch between.I try to make to when they throw the box the pottery is fine.

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Nelly    16

Dear All,

 

Another issue with shipping has to do with how it is sent off. Box within box, I have heard is the best manner to ship ceramic ware. I am not sure if you are sending stuff off in this manner but if not, this is another suggestion. Also, buttressing or supporting the appendages must be done carefully as well. Too much stress and the appendage could snap. Not enough support and the same thing could happen. I think making the unit as supported as possible is the key and ensuring that you have padded corners and box within box sending supplies. I am not sure if any of this helps but it is just something to add to the discussion.

 

Nelly

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TJR    359

I agree with Mark and Nellie. This is a shipping question, not a vitrification question. Stoneware and porcelain are stronger than earthenware. My earthenware bowls in the cupboard are all chipped, the stoneware ones are not.

When shipping, I take a larger box and build a rigid styrofoam board liner tightly inside. Then I put the smaller box in and line with styrofoam peanuts. I also wrap the piece with bubble wrap. I shipped work from Australia to Canada and broke only one teapot lid. Should have taken the lid off the pot and packed it separately within the container.

I would stick with earthenware and just look at your packing.

TJR

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OffCenter    82

Even cone 6 clays do not hold a candle to cone 10 clays as far as strength especially cone 10 porcelains

Break some of each and you will see this to be true

 

Mark... You may be right but I don't think so and I don't have the scientific instruments to prove you wrong. I work with clays fired to cone 6, cone 10, and cone 13 and if there is a difference in the strength I can't tell it without scientific instruments. Frost porcelain fired to cone 6 feels every bit as strong as Southern Ice fired to cone 10-11. As a matter of fact, B-Mix Woodfire fired to cone 13 feels a hair weaker to me than Frost fired to cone 6. (I just went out and broke some chards for a very unscientific test). When you're talking about clays fired above cone 4 I think strength depends more on the composition of the clay and it reaching maturity during firing than an almost insignificant 100 or so degrees.

 

Jim

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JBaymore    1,432

Here is an interesting post from the clayart archives on how strong a red earthenware can be, surprising results.

 

clay body strength

 

 

Good link to share there, Matt.

 

My student's MOR testing work over the years has born out the info that Pete posted. The strength of clay bodies even in the green state (green MOR) always seems to surprise them. Well formulated and well glazed fired clay can be pretty darn tough.

 

Like most "things ceramic"...... it is a bit more complicated than the simple answers provide.

 

best,

 

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

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OffCenter    82

Here is an interesting post from the clayart archives on how strong a red earthenware can be, surprising results.

 

clay body strength

 

 

Well, I wasn't surprised that I was right about strength of clay depending more on composition and firing to maturity than on temp fired to, but I was surprised to see that the strongest clay tested was a cone 04 earthenware.

 

Jim

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Pres    896

Here is an interesting post from the clayart archives on how strong a red earthenware can be, surprising results.

 

clay body strength

 

 

Good link to share there, Matt.

 

My student's MOR testing work over the years has born out the info that Pete posted. The strength of clay bodies even in the green state (green MOR) always seems to surprise them. Well formulated and well glazed fired clay can be pretty darn tough.

 

Like most "things ceramic"...... it is a bit more complicated than the simple answers provide.

 

best,

 

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

 

 

I can attest to that-Several years ago I fell asleep during a late night firing overfiring a bisque. I figure it had to have been ^8 at least as some of the ware had slight bloating this in a ^4-6 clay body. I gave my father a bunch of the casserole bottoms as planters. He tried drilling drain holes in the bottom of them with all sorts of bits, could not find a one that would work breaking a few of the pieces in the attempt.

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neilestrick    1,381

I think it may depend on your definition of 'strength'. High fired clays may be harder, but not necessarily stronger when impacted or stressed. If I understand Pete's test method, they were taking bars of clay, laying them across a gap, and snapping them in half via pressure in the middle? In that case, it makes sense to me that the earthenware was the winner. Under this method of testing, the earthenware probably has more flexibility and can deflect more than the stoneware before breaking. The stoneware/high fired clays, while tighter and harder, are likely more brittle under this type of test, and can't deflect much at all before giving way and snapping.

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JBaymore    1,432

If I understand Pete's test method, they were taking bars of clay, laying them across a gap, and snapping them in half via pressure in the middle?

 

Yup... basically that is it. Standard MOR test procedure. The un-supported span distance is 10 cm, sustained pressure located on a knife edge plate located dead in the center. Bars are post-firing machined to a precise 1 cm x 1 cm crosss section (in industry ...for accurate scientific comparison numbers). For studio potters, the actual # obtained can simply be a relative stregnth number between various test bodies.... decreases the need to such accurate test bar preparation.

 

There are other tests for brittlness and such.

 

 

best,

 

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

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OffCenter    82

I think it may depend on your definition of 'strength'. High fired clays may be harder, but not necessarily stronger when impacted or stressed. If I understand Pete's test method, they were taking bars of clay, laying them across a gap, and snapping them in half via pressure in the middle? In that case, it makes sense to me that the earthenware was the winner. Under this method of testing, the earthenware probably has more flexibility and can deflect more than the stoneware before breaking. The stoneware/high fired clays, while tighter and harder, are likely more brittle under this type of test, and can't deflect much at all before giving way and snapping.

 

 

I don't think you're right about this. I think "hardness", too, depends more on composition of clay body and that clay body being fired to maturity than on temperature. I'm almost certain a cone 6 porcelain fired to maturity is just as "hard" as a cone 10 porcelain fired to maturity and, after reading about Pete's test, I would guess that a cone 04 earthenware fired to maturity is just as hard, if not harder, than any cone 10 clay.

 

Maybe Matt can pull up something about hardness or, at least, chime in here with his opinion.

 

Jim

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Mark C.    1,807

That cone 04 earthenware fired to maturity was a surprise to me but the stuff on various glazes covering the clays was not.

Since a dry clay test is not how I sell fired pottery I feel glazed wares should be considered on overall strength of product/clay

Yes cone 6 frost porcelain is not what body I was thinking about as a standard cone 6 body used my most due to cost$$

Most of us cover our functional wares with glaze-I know we have exceptions like my salt pots or your woodfired wares but overall glazes add to the strength of pots

Just as stoneware in my cupboard is chipped and Porcelain is not-both are fired to cone 10 or 11 .This test is done over time and bears out my point of glazed wares to some degree.

Static tests are great but real world of hard knocks is better.

My stoneware wood fired pots seem to be weaker than my reduction Porcelain pots -again not with a MOR test but real world use.

Mark

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neilestrick    1,381

I don't think you're right about this. I think "hardness", too, depends more on composition of clay body and that clay body being fired to maturity than on temperature. I'm almost certain a cone 6 porcelain fired to maturity is just as "hard" as a cone 10 porcelain fired to maturity and, after reading about Pete's test, I would guess that a cone 04 earthenware fired to maturity is just as hard, if not harder, than any cone 10 clay.

 

Maybe Matt can pull up something about hardness or, at least, chime in here with his opinion.

 

Jim

 

 

I agree that cone 6 and cone 10 clay bodies can have the same hardness. I meant earthenware vs mid or high range, my bad on not being clear there. I don't think that earthenware fired to cone 04 is anywhere near as hard, though. Drilling a hole in cone 6-10 clay is incredibly difficult, but earthenware is a piece of cake. And drilling is very different than Pete's test. Hardness often goes with brittleness.

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Matt Oz    67

I think it may depend on your definition of 'strength'. High fired clays may be harder, but not necessarily stronger when impacted or stressed. If I understand Pete's test method, they were taking bars of clay, laying them across a gap, and snapping them in half via pressure in the middle? In that case, it makes sense to me that the earthenware was the winner. Under this method of testing, the earthenware probably has more flexibility and can deflect more than the stoneware before breaking. The stoneware/high fired clays, while tighter and harder, are likely more brittle under this type of test, and can't deflect much at all before giving way and snapping.

 

I don't think you're right about this. I think "hardness", too, depends more on composition of clay body and that clay body being fired to maturity than on temperature. I'm almost certain a cone 6 porcelain fired to maturity is just as "hard" as a cone 10 porcelain fired to maturity and, after reading about Pete's test, I would guess that a cone 04 earthenware fired to maturity is just as hard, if not harder, than any cone 10 clay.

 

Maybe Matt can pull up something about hardness or, at least, chime in here with his opinion.

 

Jim

 

As far as the red earthenware goes, the redart recipe doesn’t look like it has a lot flux in it, so I would think that it is porous like other red earthenware. I wonder how much flexibility does play a role, he did mention a cone 1 firing didn’t make it stronger, which I assume means it was just as strong. Could the high iron content of red clays have something to do with the results?

 

 

About difference between cone 6 porcelain and 10, from what I have read there are more and longer mullite crystals at higher temperatures, it would be nice to know how much of a difference it makes. Here is an interesting paper on the subject that seems relevant.... Mullite development

 

It would be interesting to compare a vitrified 6 and 10, under glazes with similar compression (or how ever you would do a fair comparison), then put them through a series of tests. Until then, I'll rely on everyone’s real life experience, because I only fire to 6. I'm really only curious though, cone 6 has proven to be strong and durable enough for my needs.

 

 

On a similar subject, Matt and Dave’s clays have published results on there website in the science section, showing how a cone 6 gloss glaze, using the right amount of boron, can be more durable than a 10.

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Lucy    0

Thanks much for everyone's replies. Because the cost of safely shipping work (dbl boxed, tons of bubblewrap, foam, crate inside box sometimes, etc) was getting out of hand, I wanted to think about all the variables, and strength of the clay body was one. Thanks much for the advise!

 

Lucy

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Marcia Selsor    1,301

Lisa Naples was giving a workshop and had a ceramic engineer in her class. The engineer told her that an earthenware fired to vitrification was as strong as stoneware fired to vitrification. Lisa is doing some fantastic work in earthenware and fires to cone 01 or 02. For packing sculpture you can construct styrofoam encasings to protect the parts. Then always double box or build a crate. If the size is large enough, you can take your crate to Fedex depots and ship on pallets (using your Potters council membership discount). That is a really good deal.

 

 

Marcia

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