Porcelain Survey

[glazenerd]

John:

I met this guy in KC who was kind enough to give me a couple of dilatometer tested porcelain recipes, by which to project my recipes against. He is also kind enough to let me send samples of finished product to test on a dilatometer. Closed my office/warehouse the week of NCECA, reason I had to leave mid week, so I have been pricing those little boy toys: yee and haw!!! Right now I am using lab grade potassium hydroxide to set values: the benefit of lab materials. Pricey yes, but you have absolute values with certainty.

Marcia: and for those very reasons I am not going to formulate with standard feldspar/s- zero quality control. The benefit of using technical grade materials: they ship with batch analysis sheets attached.

Biglou: I think the general standards for porcelain were set by Tom Coleman: or at least compared to. One of his most popular recipes was 1/4 kaolin, 1/4 ball clay, 1/4 silica, and 1/4 feldspar. He also had a 50 kaolin, 25 silica, and 25 feldspar. So I think the porcelain standard has become very blurry. I suppose 26% kaolin these days would make it porcelain, or 26% ball clay would make it stoneware: who knows?  If it throws like cream cheese; then it is mostly kaolin. If it has body, there is some amount of ball clay in it.

Nerd

[neilestrick]

IMHO, if it has ball clay in it, then it's a white stoneware, not porcelain. But I'm kind of uptight about that.

[glazenerd]

Neil:

On the strictest points: cannot say I would disagree with you. However, clay formulation has turned to property and behaviors more than anything else. From what I have read, and been taught recently: I think the standard lies more in Si/AL ratios in the body more than anything else. Then again that is the beauty of the pottery biz: everyone holds a certain truth because it works for them. I have seen as much creativity in applications, techniques, and work environments in this forum, as I have seen in the pieces produced.

Nerd

[Mark C.]

Yes Custer has changed and the industry needs to adjust. That has happened and continues to happen as we use up layers from th pits.Buckingham, Kingman, have been gone for a long time. It is the nature of the beast...raw materials.

Marcia

Wait a minute I still use Kingman every week-I am down to 1,000#s of the 3,000 I bought when the mine was almost gone in the  early 80's

My custard is old stock as well for the most part.

I still have some Buckingham to I think?

Its always best to buy in volumes when you can and then work off those stores of tested materials.

I realize most do not do this but it really makes sense for the long run. 

Still have a few bags of albany slip as well

I started early at material hoarding before it was a TV show.

[Marcia Selsor]

you were smart to do that. The depletion of the mines change the chemistry in many base materials are enough to change glaze results significantly.

Marcia

[glazenerd]

Since leaving NCECA in KC roughly a month ago, I have been running porcelain clay tests. Currently I am working on flux variations, combinations, and flux alternatives. Below is the result of potassium/sodium levels: Tile 1 is a standard commercial cone 6 porcelain. (lower left hand corner.) Tile 2 is roughly a 50/50% (batch weight) of sodium and potassium. (Lower right hand corner.) Tile 3 is 99.8% potassium and 0.20% sodium. Tile 4 is 25% sodium and 75% potassium. All tiles were fired in the same kiln, same shelf, and glazed from a single batch mix. The variation/s in color and crystal formation can only be attributed to the changes in sodium and potassium levels in the clay: the only variable in this test. While these flux levels will not alter most glazes, I suspect there are several they will effect other than crystalline glaze. Note: iron and magnesium levels were fairly consistent in the three custom blended porcelain bodies.

 

 

I had previously tested varying levels of iron and magnesium in porcelain bodies. Interestingly enough, Iron (FE) did not alter the whiteness of porcelain until it reached 1.25% of batch weight. However, magnesium levels above 0.60% began to show very light gray coloration. I had long thought that iron was causing discoloration of the clay, but in reality it is magnesium causing the light gray color/s.

Has anyone experienced differences in glaze color/s when you switched porcelain suppliers?

 

Nerd

 

I noticed Fred Sweet has joined the forum- welcome aboard. Remember meeting you at NCECA.

[neilestrick]

Iron is a big deal when firing in reduction, but in cone 6 oxidation it's not so problematic. 1% would be a major problem in reduction. Other impurities also make a difference. A porcelain we used to make at A.R.T. used a domestic kaolin that was slightly higher in titanium than grolleg and caused some grayness.

 

This makes total sense to me. Glazes are definitely affected by the clay. I have an iron red that is very different on each of the 4 clay bodies we use in my studio. I can identify the clay body just by looking at the glaze.

[Joseph Fireborn]

I don't know much about all the chemistry involved in crystals, but tile number 3 looks really awesome to me. I don't know if thats what you were going for, but I really like the crystal development on that tile. Doesn't look like any crystal work I have seen before. Most crystal work I have looked at looks like number 2. More of the circular shapes. Number 3 looks like spurs exploding or something. Very neat stuff. 

 

I am guessing your happy with your information you learned from your custom mixing clay meeting?

[neilestrick]

What are the absorption rates of each of the bodies? I'm wondering if the differences can all be attributed to the potassium/sodium makeup, or if there are changes in how glassy/ tight/ close to melting point the clay is getting. As the clay gets closer to its melting point it's going to interact with the glaze differently regardless of the type of fluxes.

[Min]

Are some of the crystals on tile 3 raised? I wonder if a slip made from #3 body and applied to a less expensive to make clay body than white porcelain would give similar results?

[glazenerd]

Neil: tile 2 I have not tested for absorption, but I suspect it is not fully mature due to the crystal development. Tiles 3 ran 0.15%, and tile 4 was slightly over fluxed: the outer edge is full of pinholes due to off gassing.

Joseph: had been studying clay bodies and formulations for a couple of years before meeting Ron Roy in KC. Had a very long list of questions for him when I arrived. Got to spend 3 hours with him Sunday night, 5 hours Monday, and 6 hours Tuesday- he answered them all. Learned more in that time then I did in years of reading books on the topic.

Min: the glaze is perfectly smooth- except tile 4 which had an accident.. LOL

Nerd

 

Neil- will post a series of test bars shortly; amazing how the color changes with just small changes in magnesium.

[Guest JBaymore]

 Learned more in that time then I did in years of reading books on the topic.

 

This is why people hold Ron in such high esteem. 

 

best,

 

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

[glazenerd]

John:

Getting a fair amount of one on one time with a man who has been blending clays for sixty years was worth the trip. For five years I have tried to explain my theories about crystalline glaze and clay on several forums: mostly being met with scorn and disbelief. It took me over an hour to explain the basics and it was nice to hear someone finally say- I get it. Very much aware that what I am looking at and experimenting with is far outside the norms of glaze/clay chemistry. I doubt seriously if Paulings scale of electronegativity is taught in glaze 101. The icing on the cake: meeting a man who is basically a walking dictionary, and yet manages to be a very humble and gentle man. Liz and Ron both invited me up to their place for a week: just might take them up on that. I think that week would equal a doctorate degree.

Nerd

 

By the way- when I left Tuesday it all clicked- I got it.

[glazenerd]

Test bars shown were formulated for and fired to Cone 6 (2230F)    MGO = Magnesium    FE = Iron   (oxidation)

 

Bar 1 MGO 0.33   FE 0.32      Bar 2 MGO 0.89   FE 0.36     Bar 3  MGO  0.78    FE  0.42      Bar 4  MGO  0.42  FE  0.36

Bar 5 MGO 0.63   FE 0.32      Bar 6  MGO 0.49  FE 0.40     Bar 7 MGO 0.36       FE 0.86      Bar 8 MGO 0.42  FE 0.74

Bar 9 MGO 0.97   FE 0.91   TiO2  3.77        Control Tile- top  MGO  0.18   FE  0.32

 

In oxidation: higher % of MGO causes graying, and higher % of FE causes tan/s. TiO2 can also cause coloring.

Limits shown as calculated on GlazeMaster- clay module. (Written by Ron Roy.)

 

If you are experiencing pinholing at cone 6, it may not be your glaze at all.

 

The normal potassium levels in cone 6 clay runs from 3.50 up to 4.15 %. The above tile was intentionally tested at 5.77% to illustrate how much off gassing occurs in the clay at these temps. This test tile has no glaze, the gloss was caused by the flux bleeding to the surface of the clay.

 

Nerd

 

 

 

[glazenerd]

Running some experiments on colored porcelain. The norm is to use body stains, but I decided to use oxides instead. The small test bowl below has cobalt, copper, and red iron. In addition, I decided to swap out some of the flux for frit. The piece below was fired to cone 3: there is no glaze applied.

 

I used my Coma Clay (tile body), so making a small pinch pot was a bit more work than I cared to do- but hey.

Nerd

 

[Chris Campbell]

Robin Hopper's book, 'Making Marks', has a great reference chart for using oxides to color clay.

Being lazy, I use stains.

[glazenerd]

Chris:

If I read someone's book on the topic: then I miss the joy of discovery. While I like the colorants, more interested in the self glazing aspect.

Nerd

[Saki]

1. What are the properties that you dislike the most.

I dislike the uneven drying and shrinkage. Porcelain dries very quickly, which can make trimming difficult—for example, if care isn't taken, the rim of a large piece can dry out before the foot is ready to trim. The uneven drying and shrinking also makes altering forms and adding attachments much more difficult than other clay bodies.

 

2. What properties do you find most beneficial.

I love the smoothness and plasticity of throwing porcelain.

 

3. How important is translucency or whiteness?

Whiteness is very important—many glazes, like celadons and oribes, just can't compare on other clay bodies. I suspect this is true for most users of porcelain. Considering the additional cost, I would be surprised if many people who weren't after extreme whiteness chose to work with such a finicky clay body.

I like the transparent effects on slip cast pieces, but I have found that if I throw thin enough to achieve translucency, the piece inevitably warping during firing.

 

4. Would you make larger pieces if the clay had the mechanical strength?

This hasn't been an issue for me. I have thrown pieces up to 24" tall or wide (large for me). It just requires more trimming.

 

5. What cone do you fire to the most?

∆6

 

6. What properties do you wish porcelain had?

Slower, more even drying (see #1)

 

7. Do you throw, press, hand build, etc?

I primarily throw. I also occasionally slip cast. Rarely, I add ornamentation/sculptural detail to thrown pieces by hand building.

[Guest]

Tom was kind enough to send me some of his porcelain and I have been playing with it for the last three days. I can only compare this clay to the 6 different stoneware and 1 different earthenware clay I've played with. If I seem a little bias its because of  I never worked with porcelain before.

 

DAY 1

To start I decided I would take two 1 pound chunks with the intention of throwing and wedging the each a few times. Out of the bag I noticed the clay is softer than what I preferred and at first it reminded me of my nemesis clay, standard 630. With the first bit if clay on the wheel plunged ahead.

 

Centering was as expected and quickly plunged my thumb into the clay then proceeded to make my first pull. Honestly I pulled to quick and to thin the first pull and surprisingly it stayed perfectly in shape. I'm talking from 1' walls to less than 1/4" wall. I said to myself, yeah this is better than the 630.

 

I played with it a few more moments and then wired it in half to find the walls were around 1/8" thick and until I wired it in half it was pretty stable.

 

I gathered as much of the clay as possible, I know Tom is meticulous with his formulas and I didn't want to changes its composition to much and left it on a plaster wedging table.and stated on the second ball.

 

I was throwing a thin bowl about 6"-7" round and decided to gather up the clay and go back to the first ball. I coned up on the bowl and as expected it got all wobbly which it did, what wasn't expected was that it popped back into a tall shape and was IMO a usable form.

 

I threw a unlidded jar with a narrow foot to see if the clay would sag. I'd say the foot was about 1/3 the size of the waist or the widest part. I also threw to about a heavy 1/8" thick. It my surprise it didn't sag

 

 

I threw and rewedge each ball about 3-4 times each.

 

DAY 2

I decided I would throw 2 ginger jars and a handled mug.

The mug came first and I was using some of the clay from the day before. I've read somewhere that you couldn't do this with porcelain, I don't remember if this was stated as a fact or if it was someone's opinion. Its possible I may have misunderstood this too, because this clay threw better than the day before.

 

Next came the two lidded ginger jars. All went smoothly with no surprises. I threw the two lids off the same hump with the remainder to be used as a handle the next day.

 

I had the air conditioner on and it looked to me like the clay was drying to fast so I place the three pots and two lids in a plastic bag.

 

DAY 3

I took the three pots out of the bag and they looked perfect for trimming so the first thing I did was use the leftover clay from the day before and extrude a handle which went perfectly without a hitch.

 

As per Tom's recommendation, I left the two ginger jars on the bat until they popped off, but first I trimmed the rim on the jar to fit the lids and trimmed the lid and what I could with the jar. Tomorrow I'll trim the base/foot.

 

I decided to remove the mug from the bat, trimmed it and installed the handle, all went as expected.

 

My thoughts on this clay

I love this clay, I know this might sound silly but it felt like the clay was reacting to my thoughts instead of my hands. I used very little water while throwing in fact the bits of clay left in the pan was between leather hard and bone dry. One time the clay dried so quick on my hands that it started to flake off and landed on the clay I was throwing. I was able to rib off the unwanted speckles. Side note: the air was not blowing on me or the clay.

 

This clay was responsive and a joy to throw. The clay was soft enough to cone and center quickly while being stable enough to hold its shape without flopping over itself when throwing aggressively.

 

Negative thoughts on this clay.

A review isn't worth the read if there wasn't some negative comments and it didn't take me long to know what they were.

1) This clay isn't on the market and I can't buy any which makes it impossible for it to be my favorite clay. The problem is it is my favorite clay.

2) I really dislike Standard's 630 because of this clay

[oldlady]

wow!  just think, you are in on the ground floor of a potential PERFECT SOLUTION! 

[glazenerd]

Ron:

Thank you for the kind words and honest assessments.

 

A proprietary formula, so I will not expound too much. It is an SAS formulated body, with a plasticity index of 8.74 CEC meq. There are two different plasticizers, with a third organic stabilizer ( food safe). Combined, they achieve moisture equilibrium: meaning one holds water and the other sheds water. The dried bits on your fingers dried quickly, but also hydrated immediately. All you have to do is dip two fingers in water; wring your hands to hydrate, then throw some more. It is designed to work with a minimum amount of water.

 

This body is pure porcelain, by existing pottery standards. I used my formula limits to calculate the properties. By the way, it has the same moisture content as most clays: it just " feels" soft- and that was calculated as well. I formulate per specific use and cone: this body is also formulated with extended drying times (2-3 days) for sculptural and hand building techniques.

 

Lastly, in order to formulate this body: I forsook traditional formulation criteria, and wrote my own!

Nerd

[glazenerd]

Ron said: "The mug came first and I was using some of the clay from the day before. I've read somewhere that you couldn't do this with porcelain, I don't remember if this was stated as a fact or if it was someone's opinion. Its possible I may have misunderstood this too, because this clay threw better than the day before."

 

 

By the way- sodium creates this problem.

[Mark C.]

you were smart to do that. The depletion of the mines change the chemistry in many base materials are enough to change glaze results significantly.

Marcia

The reason I drove out of state back in the day (early 80's) to get a lifetime supply  of Kingman was this .It was the only ingredient that made my favorite glaze at that time work so well-That glaze was Wamo Mamo II I(1/2 the tin) on stoneware which is still my most favorite glaze (I cannot get that on porcelain or in my current reduction fires with all white bodies.

[glazenerd]

Colored porcelain on the left, butter/ cream stoneware center, and red/ brown stoneware on the right. After years of researching, finally getting around to making some clay. Just need to learn how to throw.

[Guest]

Tom, when I bisque fire the two jars, would it be ok to keep the lids on?