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Starting With Porcelain


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I bought a couple of bags of cone 6 porcelain.  I don't remember which clay it is. I threw some pots and am ready to fire.

 

1.  Can I tumble stack the bisque fire?  I had read that porcelain needs a special kiln wash.  Is that with glaze fire only?  With the porcelain pots stick to each other during the firing?  can I stack stoneware pots with the porcelain?

 

2.  I made some slip with the porcelain clay.  I covered some red stoneware at leather hard with it.  I tried to do some decorative finger swipes in the slip.  Didn't work well.  Do I need to add other ingredients to the slip to get the kind of look I am going for?  What are the chances the slip will stay on the pot through the bisque?  I had heard not to mix stoneware and porcelain.  Why is this?  I have read several time of porcelain slip on stoneware...

 

Any and all other suggestions are welcomed.

 

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1. Porcelain may sometimes stick to kiln shelves during glaze firings  -- it's called plucking.  Add some alumina hydrate to your wax and apply that to the bottoms and you should be fine.  Some potters will add a drop of food coloring so you can tell that wax from your regular wax.  At bisque, you should not have any problems due to the lower firing temperature.  As for stacking, no reason for tumble stacking not to work.  Of course, pieces that are really thin or have delicate features might want to be done separately to avoid damage. 

 

2. I use Highwater's Helios Porcelain (cone 7 - 10) to make slip . . . for use on Little Loafers, Red Rock and other stoneware at cone 6 with no problems.  For my items, I apply the slip while still fresh slabs or soft leatherhard so the slip has time to dry with the clay body.  Doing finger waves and similar techniques seems to me to be a matter of timing and thickness of the slip application.  Maybe practice on some slabs to find the right timing and thickness to get the look you are trying to achieve. 

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You can treat the porcelain just like any other clay when firing. Stack it in the bisque.

 

If you have kiln wash on your shelves you shouldn't have any problems with plucking, and don't need the alumina wax on the foot.

 

The slip has to be fairly thick and still quite wet in order to do finger wipes.

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Only if about stacking stoneware with the porcelain is if it rubs and puts a dark scratch on the with porcelain. As long as they aren't moving around, just uniformly shrinking, you should be ok. I just label wax that has had alumina added to it. It works to avoid the plucking.How did you like throwing porcelain?

 

 

Marcia

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It's been said that throwing porcelain is like throwing cream cheese.  Sometimes I miss the strength and plasticity of stoneware, but I'm pretty committed to porcelain at this point.

 

I've always been fascinated by glazes and surface treatment, and also I like representational art of many sorts.  The surface of porcelain is more akin to paper or canvas than the surface of stoneware.  Also, at least for me, there is the possibility of greater subtlety and range in the surface of porcelain, because of the lack of iron, which seems to affect the color of stoneware and stoneware glazes so much.

 

Of course, there was a time when I threw with Lizella clay and put a white slip over it.  Sgraffito into a dark clay through a white slip has all sorts of nifty drawing potential.  But all in all, I like the cheesy white stuff a lot.

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Thanks Everyone,

 

Marcie,

I really like the porcelain. It was so responsive to the touch. I like my clay very soft to throw with but left the clay firm for fear of making a big pile of slip. The best part was how quickly it dried. I currently switch back and forth between red and white clay. I think this would be to much work with the porcelain. I saved the last half bag to make some slab plates to decorate.

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I don't use porcelain much as I hand build but lots of people do at our studio. we highfire and the porcelain goes in the bisque with all kinds of other stoneware and I don't think it gets any special handling or treatment. One thing I have seen is that glazes can run off the pot more easily due to the smoothness of the porcelain so maybe a thinner application.

hmm, makes me want to go work with some cream cheese.   rakuku

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Its not running off the pot because of smoothness , its running off the pot due to the makeup of the clay body.. That's where people struggle making glazes for porcelain as compared to other clay bodies... I will have to reread the chapter but I think it contains some type of fluxing agent .. so you take a glaze recipe with a relatively moderate to high flux + whats already in the Porcelain then it wants to be like Niagra Falls...

 

someone correct me if I don't have this nailed down.. I think it close though..

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Correct, smoothness has nothing to do with it. White stoneware bodies actually tend to be finer-grained (smoother) than porcelain. I think the bigger issue is the thickness of the glaze in application. If you compare porcelain and stoneware bodies that have been bisque fired to the same cone, the porcelain is much more porous. So if you dip both in the same bucket of glaze for the same amount of time, the porcelain will have a thicker layer of glaze on it than the stoneware. And we all know what happens when glazes are too thick. I see this all the time with my students when they use porcelain for the first time.

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Correct, smoothness has nothing to do with it. White stoneware bodies actually tend to be finer-grained (smoother) than porcelain. I think the bigger issue is the thickness of the glaze in application. If you compare porcelain and stoneware bodies that have been bisque fired to the same cone, the porcelain is much more porous. So if you dip both in the same bucket of glaze for the same amount of time, the porcelain will have a thicker layer of glaze on it than the stoneware. And we all know what happens when glazes are too thick. I see this all the time with my students when they use porcelain for the first time.

 This is a very helpful observation! I have a bunch of glazes that I just love, but they seem way too thick after firing. It didn't click that this was what was happening until you mentioned it. Going to try a thinner application and hope I still get the same nice colors, with less pooling at the bottom.

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