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Cone 6 Porcelain vs Cone 10 Porcelain

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Hi everyone - hope you are well, just finished a show - was really good!

 

Does anyone have any experience using Cone 10 Porcelain?

 

I normally use Cone 6, but am finding its very "clay-like" and not giving me the fine, smooth finish I was used to with the porcelain we used in the 90s. I also noticed Cone 6 wasn't as strong as I would like, so hopefully Cone 10 will be better in these aspects.

 

I have ordered a box of Cone 10 English Porcelain and will be trying it out.

 

Question regarding Cone 10 Glazes - are there any commercially available Cone 10 Glazes? I can't seem to find any. My pottery supply shop said that most ppl make their own Cone 10 glazes and I really don't want to get into that! (yet....)

 

If not, can I use my previous Cone 6 glazes? I don't have to worry about food safety as these are for smaller jewelry pieces.

 

I previously used a lot of low fire glazes on my Cone 6 Porcelain with no problems in terms of crazing etc.

 

Your thoughts and experiences would be greatly appreciated!

 

 

**EDIT: Not sure which forum this would go in, Sorry if I made an error!***

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Hi everyone - hope you are well, just finished a show - was really good!

 

Does anyone have any experience using Cone 10 Porcelain?

(I use about 10 tons a year of porcelain for more years than I can recall)

 

I normally use Cone 6, but am finding its very "clay-like" and not giving me the fine, smooth finish I was used to with the porcelain we used in the 90s. I also noticed Cone 6 wasn't as strong as I would like, so hopefully Cone 10 will be better in these aspects.

(Funny you noticed this as many do not believe this is true-I am with you on this point)

I have ordered a box of Cone 10 English Porcelain and will be trying it out.

(there are many cone 10 clays to try)

Question regarding Cone 10 Glazes - are there any commercially available Cone 10 Glazes? I can't seem to find any. My pottery supply shop said that most ppl make their own Cone 10 glazes and I really don't want to get into that! (yet....)

(Yes you can buy them from places like Laguna clay co.)

If not, can I use my previous Cone 6 glazes? I don't have to worry about food safety as these are for smaller jewelry pieces.

(I think cone 6 glazes will run off at cone 10 but have never tried it so its an educated guess)

I previously used a lot of low fire glazes on my Cone 6 Porcelain with no problems in terms of crazing etc.

 

Your thoughts and experiences would be greatly appreciated!

(You will not be able to use low fire glazes at cone 10

You also should look for oxidation glazes for electric use as that is what I assume you are firing in?

Good luck with the switch-there are many books with glaze formulas in your cone range. And as a bonus the clay throw better than 06 clays)

 

**EDIT: Not sure which forum this would go in, Sorry if I made an error!***

 

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If you are buying Cone 10 porcelain for its strength you will have to fire it to cone10 to get that strength. If you use cone 6 glazes on cone 10 porcelain it will most likely craze and the clay will be punky...i.e. immature. I disagree with your assumption that cone 6 porcelain isn't strong. If you fire a clay to maturity, it will be strong. What cone 6 porcelain have you been using. I have used Archie Bray cone 6 porcelain, Frost, Alligator Clay cone 6 porcelain and probably some others. Those three I named seem quite strong in Oxidation and reduction.

Marcia

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Thank you for the reply Mark and Marcia - I appreciate your input.

 

I got my cone 10 porcelain but haven't used it yet as I am getting ready for a show and decided to go with what i know (cone 6 porcelain) in the meantime.

 

My question regarding glaze use wasn't clear - I wanted to know if I create a piece from Cone 10 Porcelain, and fire it to Cone 10, could I THEN use cone 6 or low fire (04/06) glazes to decorate? Or will I face issues?

 

I have done this with Cone 6 porcelain with no problems (Fire the piece to Cone 6 and then do a lower glaze firing).

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Two community arts centers where I have worked have both cone 6 (electric) and cone 10 (gas/reduction) firing and glazes available. Some of the ^6 glazes are fabulous at ^10, some are terrible. You could get some spectacular results, or the color could burn out and the glazes could run like crazy. Each glaze is different, depending on the balance of ingredients in the formula. I suggest that you test all of your current ^6 glazes on the inside surface of some bowls, fire them up to ^10, then evaluate your results.

 

BTW, I also agree with you about the differences between ^6 and ^10 porcelain. I very much prefer the finished results I get when I use the ^10 porcelain.

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Cone 10 porcelains can sometimes be a little bite glassier and whiter, but as far as smoothness and strength go there isn't any difference. I throw cone 6 porcelain, Standard #365, and have no trouble with getting the surfaces smooth. Plus, smoothness only matters to a degree you're going to cover it with glaze anyway. If you want something really smooth, then go with a white stoneware. The ball clays that are used in those are much finer than the kaolin used in porcelain, and the clay percentage is higher, too. You'll sacrifice whiteness, though.

 

I think you'd be better off trying a different brand of porcelain rather than switching your entire glaze pallet to a higher cone. Changing everything like that can takes months of testing to work out the bugs. Plus you'll be putting A LOT more wear and tear on your kiln if you plan to fire electric. There are some cone 10 glazes available on the market, but not a lot. Most people who work cone 10 mix their own.

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Over the last several years I have tested most of the available commercial porcelains and a lot of porcelain from recipes and by far the whitest, most translucent cone 6 porcelain that rings like a bell (a test of hardness) is Laguna's Frost. For cone 10 I've found nothing whiter, more translucent, or with a harder sounding ring to it than Southern Ice which is made from the purest kaolin in the world from New Zealand. Laguna makes a cone 10 Frost, but I prefer Southern Ice for cone 10 because, while it is no whiter or more translucent than Frost, it is easier to work with and doesn't crack as easy as Frost. Frost flashes in a wood firing and Southern Ice does not. The problem with Frost is for some forms no amount of working and compression will stop it from cracking. Adding paper to it does prevent cracking without costing any whiteness or translucency.

 

Jim

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Guest JBaymore

If you actually want to know the general strength of a clay body, a basic Modulus or Rupture (MOR) test will give you some hard data to look at. This is not hard to do at the "potter level" of science. If, with the error that the casual approach we use induces into the equation, the numbers are so close as to be very, very similar... probably the two bodies are about the same for all intents and purposes for your usage.

 

Make some test bars of the clay body in question about 15 cm long and 1 cm by 1 cm in cross section. These nedd to be carefully and precisely formed. Fire them to maturity lying flat on a support shelf with cone packs right next to them to assure that they are fired as you THINK they are fired. You should do at least 10 pieces of each clay body you are testing.

 

Find / make some small trangular cross section supports (like small prisims) that you can then balance the clay test bars on so that they can be supported on only two knife edge points.

 

You are going to try to break the bars by pressing down on the center point while the bars are supported on the knife edges.

 

Using a pencil lightly mark the EXACT center on each of the fired test bars.

 

Spread the triangular support points apart exactly 10 cm and spanning a space between two tables with overhanging top surfaces......... knife edge to knife edge. (For the reason for the two tables see below.)

 

The space between the two tables must allow you to hang a small bucket with a plain metal bail handle (narrow point of support contact) from the exact center mark on the clay test bars. So you need table tops with projecting "overhangs".

 

You will then slowly add weight (wet clay works) to this bucket until the clay bar JUST breaks. Then weigh the contents of the bucket and the bucket itself. Record the weight results. Repeat for all 10 bars of one clay.

 

Add the numbers together and then divide by 10. This is the average result of your test

 

Then repeat this process for all the other test clay bars.

 

Compare the results between the two bodies. The one with the higher average numbers is the generally stronger*.

 

best,

 

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

 

* This simple MOR only tests ONE measure of possible stregnth in a body. But it is close enough for most purposes.

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Guest JBaymore

John,

 

Do you need to account for differences in shrinkage when making the bars . . . so that they are equal in size after firing, not when cut from moist clay?

 

Bruce

 

 

Bruce,

 

If you want to compare to actual M.O.R. numbers used in industry (places like ASTM).... then the FIRED bar needs to have a cross section of exactly 1 cm x 1cm to a very fine level of accuracy. And the supports need to be specific to industrial standards, and the pressure point needs to be a knife edge also, and so on and so on. Industrial MOR tests are very specific. The bars are machined after firing to the appropriate dimensions to very tight tolerances.

 

But this is "potter science" we are doing here,...... and "close enough for government work". ;)

 

 

If you do your tests exactly the same way every time....... you could make them any way you wanted.... you just could not compare the numbers you got to anyone else's tests unless you BOTH did it the same way.

 

I've had my students do this work in my materials classes. Forming methods for the bars DO affect the MORs.

 

And if you want an interesting study..........

 

Everyone "knows" to add grog to make clay bodys "stronger" for more sculptural work. Well... ... do a fired MOR test on the same body with grog and without grog. It will surprise you. Grog facilitates drying in large pieces though.

 

best,

 

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

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Everyone "knows" to add grog to make clay bodys "stronger" for more sculptural work. Well... ... do a fired MOR test on the same body with grog and without grog. It will surprise you. Grog facilitates drying in large pieces though.

 

 

 

I think people often forget to differentiate between wet strength, dry strength, and fired strength.

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I can't find it now (didn't look real hard) but a while back there was a thread about clay strength. One production potter here said that clay fired to cone 10 was "obviously" stronger than clay fired to cone 6. Somebody brought up Pete Pinnell's MOR tests that showed that proper firing to maturity was what was important, not how high clay is fired. If I remember correctly, there were two other very interesting results: (1) Grog weakens clay significantly. (2) Of all the clays fired to various cones tested, THE EARTHENWARE THEY TESTED WAS STRONGER THAN ANY OF THE PORCELAINS AND CONE 6 AND CONE 10 STONEWARE.

 

Jim

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Guest JBaymore

Yup Jim......... my class's tests over the years bear this out.

 

That thread you mention is burried somewhere in here. Too many cobwebs. ;)

 

best,

 

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

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