Choosing a clay for slip casting big pot

[Textree]

Thank you again. I was thinking the buffalo wallow type and the 213 porcelain mixed something like 50-50 or 66-33 and throwing in a few (3 or 4) lbs of kyanite. Just because a bonsai potter said he has found it helpful and I was reading that some porosity makes good slips as opposed to plasticity . as for it being vitreous I don't think 0 percent absorbtion is necessary. Both those clays are approx. 1.7 I think ... I think something mostly or semi vitreous is sufficient. Would those two clays and kyanite be more or less off white at cone 6? I don't want any unglazed part (around the feet or inside or underneath) to be bright toilet white. 

[Chilly]

If you're going to leave the pots outside, and you get frost, you need those pots fully vitrified.  Guess how I know?

[Textree]

I'm guessing you have had some pots crack. I've heard people who live in the Midwest talk about pots breaking. And people saying they need to be completely vitreous but I think most of the time people use stoneware. Am I wrong in thinking stoneware generally isn't 0.00% absorbent ? I thought it was just very close like .3% and that if you over fire stoneware it can actually make it less vitreous 

[Min]

Absorption doesn't have to be zero, there is open and closed porosity which can make a difference but at 1.7 I think you will be fine. Not sure why you want to go to the work of wedging porcelain into the stoneware? I'ld give the supplier a call and ask if they have a clay body with low absorption suitable for outdoor use that contains sand or grog. You can always use an oxide stain on the feet if the colour of the fired clay is too light. Can you get Laguna clay? They have some good outdoor claybodies too. I would suggest starting another thread asking if anyone has recommendations for an outdoor claybody in Texas suitable for handbuilding.

[Textree]

That's the thing I don't want to wedge 75 lbs or more of clay together - sounds like a lot of work ... Correct me if I am wrong but if I mix it up as a casting slip then I don't have to. I will mix the moist clays in a trash can with more water with the drill mixer , let it dry out , bust it up , remix it thoroughly with the darvan and water . that way it gets two mixes. 

The ceramic supply store doesn't have a stoneware porcelain mixture . I don't want to mail order 75 or 100lbs of anything.

I started building the wood positive. Its big! Is something this size (more like 17.5 x13.5 ×5  now) going to fire thoroughly in the standard cone 6 firing if say the walls are 3/4 of an inch thick? 

[Mark C.]

I think adding a few clay types to a barrel of water and hoping for good end results in slip casting  with some darvan and water may be a little optimistic . I suggest testing your body out in smaller quantity 1st to see if will work.The reason you supply store has no Porcelain and stoneware mix is its very un-orthodox. Again I suggest trying a small amount 1st.

Why do you want this two kinds of clays together?

The other question is about bonsai pots which usually are small to begin with ,is this giant one for some special reason ? or everything bigger in Texas?

[Textree]

As for doing a small test first. That sounds like good advice. Will do.

As for mixing them I guess I could keep it simple. Save myself some time and money. 

As for the size of the pot - bonsai pots are small relative to the tree inside them. I have lots of smaller pots , (some shohin size that you can hold in your palm , some larger) A bigger one is harder to find and can be really expensive. But assuming normal shrinkage this would end up say....15× 11.  (The wood positive is actually 17.5 ×13.5) That's really not out of the ordinary at all. Its large, but I've seen rectangles as big as 20 inches long . and I know lots of people with bonsai it takes 2 men to move , lift, and work on. 

[Mark C.]

I think a slab drape or slump mold is your best option-the best is the slump into  mold form as then when the clay dries it shrinks away from mold and does not crack.The only reason to make a mold in my view is to make many items not just one..as you could one off this out of wood easy with slabs.

Use a clay that is forgiving in terms of manipulation -If you need it to be bonsai colored use a stain after bisquing it.A clay like Big white fired to cone 10 would work or big red or LB blend  all Laguna bodies.

It will be easier -way easier than slip or slip cast molds.

[Textree]

The studio just does cone 6. Although it sounds really cool otherwise . for a monthly fee I can come and go whenever 24 hrs. And they'll show me how to use everything. The ceramic store only has a couple things that are vitreous enough at cone 6 . So ill probably either do the armadillo buffalo wallow or 213 porcelain. They also have laguna frost porcelain, standard very plastic 551 porcelain, and an armadillo porcelain that's a little less vitreous than the 213 . the other midrange stoneware they have is either really dark colored or they say it may bloat at cone 6 

I guess I could order something but I think shipping charges on 75 lbs of clay might be pricey 

 

[Textree]

As for "bonsai colored" and staining it, your advice is in line with conventional  wisdom . its a large masculine bonsai pot it shouldn't be too colorful. Unglazed or some kind of oxide wash would be pretty typical. Ill glaze mine, but something tasteful not too showy or flashy