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Meridianfrost

I Love This Forum! Throwing Clay Question (Noob)

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Hello everyone! I'm getting better and better at throwing clay, and I have a question about what clay bodies everyone uses to throw. I have been using Standard 213 cone 6 porcelain, and I can't help but notice that the clay is stiff, and doesn't stretch very well. Looking at some videos online, I have seen how elastic some of the clay seems. The video in the link below is what inspired me to start throwing in the first place.

 

Look at how great the plasticity of that clay is! I have attached a picture of the box I threw last night. I rolled a slab for the top and rolled a texture mat into it. It is the first one I have attempted. Trimmed and chattered this morning. I'm getting really excited about my gradually improving abilities, and I want to expand my scope of projects. The box in the picture was made with the 213 from standard clay. Do any of you have any suggestions for a more plastic high-fire clay body? I realize that shrinkage and warpage is an issue with a more plastic clay, but I would really like to know your thoughts on the clay bodies you like. Thanks very much! You all have been very helpful! 

post-67463-0-80891100-1440167091_thumb.jpg

post-67463-0-80891100-1440167091_thumb.jpg

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Nice box!

 

One problem you may be having is that porcelain in general is less plastic than stoneware, and is more difficult to work with.  I have not used the porcelain you mention, but I do use Standard's 130 porcelain for Cones 7-9.  I've gotten used to it, and can make it work for what I make, but I'm still somewhat envious of potters who use stronger and more plastic bodies.  I used to work with stoneware, and it's easier to get extended forms with a good stoneware body.

 

I use porcelain because rich colorful glaze surfaces are very important to what I make, but if glaze was secondary to form for me (and if I hadn't spent many years already working with the somewhat more limited palette of stoneware) I'd change back in a flash.

 

For me, that white smooth canvas is too seductive to give up.

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I like using clay that mixes stoneware and porcelain (I don't know how's it called in English, it is Grès porcelainique in French). It is very smooth, amazing to throw. You can throw it pretty thin too.
I used to throw a B-mix clay, that was wonderful too (not sure if this one is a mix or only a stoneware)

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Stiffness and plasticity are two different issues. If the clay is stiff, that simply means that it has less water in it. You are at the mercy of the clay supplier as to how much water they put in their clay bodies. It will vary from batch to batch, as there is a range that they find acceptable. You can add water by poking the clay full of holes and putting it in a plastic bag with a little water for a few days. Then you have to wedge it.

 

Plasticity has to do with the formula of the clay body. Porcelain bodies are the least plastic, as they are very low in clay content by comparison, and the clay that is in them is not very plastic. If you need more plasticity you'll need to switch bodies.

 

As for that video, it's impossible to tell how stiff or plastic that clay is by watching. Any professional potter is going to make it look easy regardless of the qualities of the clay body he/she is using.

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It's also worth mentioning the thixotropy of clay, especially with high kaolin contents. Get the clay moving prior to putting it on the wheel, or cone it a couple of times before pulling. It makes a huge difference.

 

Also, you don't need a body that stretches well for that you're making, especially with how much you're trimming. But, if you do start needing a stretching body, I've found great success with white stonewares (porcelain with ballclay:P) in terms of stretching on the wheel. For handbuilding, a plastic stoneware like soldate 60 is tops (for stretching).

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hey,

     When ever I get ready to throw I check out the clay to see if it is acceptable to throw or not.  If I'm throwing 3 cups suitable

for selling to the public, I'd weigh 6 lbs. (since I'm going to cut it into thirds)  then I'd try wedging it to see if its soft enough

to throw...OK, it wedges but I'm not sure if it is still soft enough... so I make the 6 lbs into what is a cone shape i.e.

1/2 of an American football.  Then I take an ordinary wire tool and try cutting thru the top quarter of the cone.... If the wire

tool causes the clay to tip over, I start slicing the clay in 1/8 in slices, adding water in between.  then turn it on the side

and repeat slicing again and adding water.  I do this about twice then wedge it back together and see if the wire tool passes thru the  clay with out tipping it over.  When the wire tool will pass thru the clay with out any help (holding in place with

the thumbs), then I know the clay is wet enough to wedge and then throw.  So cut and wedge, cut and wedge til

none of the air you put in with the water is visible any more, the cut the clay into 2 lbs units and throw.  This is how I

prepare the stoneware clay....and my porcelain clay...(Highwater Helios)  This way, the clay is always

consistant whether I'm using someone else's clay, or using clay I bought last year.

    I found it easier to do the slicing and adding water before adding it to the pug mill...otherwise, if you're trying

to meter in the water to a BlueBird pug mill and add too much, it just spins until it decides to start moving clay

again.  That way, I can just wedge it as it comes out of the pug mill, and throw.

   This is how a unorthadox potter with Obssessive Compulsive Disorder prepares his clay...Oh, I do the same with

the natural dug clays too, but take the time to clean roots off the wire tool or push them back into the clay.  (depends

how much roots that unit of clay needs.

Anyhow,

Hope this helps you develope you own method of preparing clays.,

Alabama

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I remembered an interesting post by John about different porcelains. That could be why some clays you see look very different. I always find the porcelain I buy really tough, stoneware with a bit of grog is a much easier and forgiving clay to throw with.
 
 

"True" porcelain is a composition of just a kaolin and a single ground rock  - called p'tunse.  It is a high silica content feldspathic based rock.  Often also called "Porcelain Stone"   ç£å™¨çŸ³ )  Neil's basic "recipe" above would approximate a true porcelain (no ball clay) ....in basic chemical composition. Not particle size or distribution.

 

Might be a "Lost in Translation" moment.  ;)  

 

In Japan clay bodies are almost always wet blunged with a great excess of water from far less pure materials, through repeated smaller mesh screenings as it is moved to different blunging batches, and then is filter pressed to remove the last excess water.  This process produces really good quality clay out of materials that we would think of as "inferior" or "primitive" by our industrially refined standards. 

 

In America we tend to mix clay direct to the plastic state from industrially beneficiated (dried and airfloated, etc) clays with just enough water to make it workable.  This is NOT the way to make really good clay.  It is the way to make cheap (production-wise) clay. 

 

If we took the same kaolin and ground rock the Japanese (and Chinese) use for porcelain, and mixed up a body the way US suppliers typically do.... it'd likely be totally un-useable for forming.

 

The reason this labor and machinery intensive process  'works' in Japan is that the valuation for ceramic work is generally higher there.  And they are willing to have material cost a higher percentage of the sale price (indicating respect for good starting materials). Many ceramic centers mix up their own clays from mostly local materials (hence the visual distinction between pottery "villages" work).  Clay prices from suppliers in Japan in many/most places would shock you.  In America... many, many potters will go to another supplier if the price of a pound of clay is even one cent more.  No incentive in most cases for our suppliers to make better clay.

 

If that clay you got to feel was brought from Japan, Chris, it likely was produced by the blunging and the wet filter press method.  That is likely a portion of the buttery quality you mention.  And the repeated screening and settling process will take out the large particles so that is another part.

 

PS:  For porcelain (in Japanese "Jiki"   ç£å™¨  -gee key-), often in the blunging there is a huge magnet suspended in the tank with the mixing slurry... to take out the hematite (iron) nodlues.

 

best,

 

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

 

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