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Beginner Needs Suitable Clay For Bonsai Pots

bonsai; frost resistance

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#1 mrcasey

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Posted 09 August 2013 - 11:37 AM

A local community center in Parkersburg, WV has a pottery studio where I’ve been learning about pottery (about 2 months). There are 2 electric kilns in which stoneware is fired to cone 6 ( they also do some stuff with terra cotta).

 

I’d like a dark brown cone 6 clay that will withstand freezing/thawing cycles. If I understand correctly, this means that I want a pot with a very low moisture absorption rate? The pots I’m building are about ¼” thick walled rectangles 16” X 13”X 4” and smaller.

 

I live about an hour from Byesville, OH in which there’s a Laguna Clay distributor. Is Laguna a good place to get the clay with the specs I’m looking for or should I be looking elsewhere?

 

thanks,

Casey



#2 neilestrick

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Posted 09 August 2013 - 12:49 PM

Standard 266, fires to cone 5. Beautiful dark brown/black color, great workability.


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#3 Biglou13

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Posted 09 August 2013 - 01:22 PM

I made a few with standard 266, im aslo playing with slip, wash, engobe, over lighter clays for that darker look seen im many bonsai pots.
I'd be a little concerned with slumping while firing...add extra drain holes for drainage. And extra tie down holes. There are great videos on line about bonsai pots. I think 1/4 inch wet clay is too thin for larger posts . I also added grit to clay for a little extra stiffness and less shrinkage.
I've also seen where some will place wadding under large pots to help with slumping with large ones.

you cant always trust the vitrification rule for given clay make sure to test freeze thaw cyle, easy to test is absorbtion % in fired clay body. Nor can you trust the color of clay from pictures.

Of the laguna clays I'm your area the wc 613 and wc 614 look like good candidates and with low absorption rates at cone 6
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#4 neilestrick

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Posted 09 August 2013 - 02:36 PM

I've made 40 pound planters with standard 266 without problem. Just don't push it past cone 5.


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#5 jrgpots

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Posted 09 August 2013 - 04:25 PM

Ask Big Dave.  He makes them for a living.  He used to be on the forum, but I have not seen him for about 2 months.  His website is www.bonsaiartisans.com  .  Try him there.  He should be able to give you all kinds of info. 



#6 bciskepottery

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Posted 09 August 2013 - 05:33 PM

Here is another potter who makes bonsai ware  http://taikoearth.com/



#7 Biglou13

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Posted 09 August 2013 - 08:57 PM

I've made 40 pound planters with standard 266 without problem. Just don't push it past cone 5.


Isin't. 266 a cone six clay? The reason I'm extra cautious about slumping is that bonsai pots have some very strict requirements. One is water can sit stagnant in pot.....all water must drain. So even a very slight slump with out drainage, can kill extremely valuable tree. One rule about bonsai pots I don't understand is, minimal amount of glaze on inside of pot? But it is meeting specific requirements then matching appropriate pot, shape, size, color ,matte or glossy to species, size, design of tree that is difficult. Hence the relatively high dollars paid for good Bonsai pots.
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#8 mrcasey

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Posted 09 August 2013 - 09:26 PM

Neil - That standard 266 has the most appropriate color I’ve seen so far. It’s dark and elegant. However, since it’s a communal kiln and everybody else fires to cone 6, I can’t imagine the overseer will allow me to fire a partial batch of cone 5 pots.

 

Biglou13 - Since ¼ inch wet is too thin, is there some standard ratio for wall thickness that would be safer?

Eg ¼ inch thick for every 8 inches of rectangle length?

Also, if I “add grit to the clay”, will it make the fired body more water absorbent and thereby give me freeze/thaw problems?

 

There are a number of bonsai pot artists online. I often look at their wares and wonder how it is that they get such perfect symmetry with beautifully clean lines and curves.  I also never see any marks where their fingers and tools have been.  I’ve built 8 pots so far. I’ve recycled all but 3 of them. None have been fired. I’ve got the proportions pretty much the way I’d like, but I still can’t get that finished look I see in professional quality pots.  Here’s my latest attempt. It’s about 12 inches long.

 

 

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#9 bciskepottery

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Posted 09 August 2013 - 11:06 PM

Biglou13 -- 266 can bloat at a hot cone 6; I bisque 266 to cone 05 to try and burn out impurities. Still, from time to time I get some bloating during glaze firing. As for not glazing the inside of pots, some plant roots (I've been told) will not grow properly or spread in a glazed interior and prefer unglazed interiors to get better root growth. I've done it both ways -- glazed and unglazed interiors -- and let the customer choose which one -- they know what plant is going in it and what type of root ball the plant has. For unglazed, most seem to glaze down to the likely soil line and leave everything unglazed below that point.

Mrcasey -- nice looking pots. As your pots become bigger, you need to increase the wall thickness to give it stability and to prevent slumping and warping. Not sure what the ratio is, but you will recognize it when you see it -- the symmetry will be evident. Are you forming from slabs or extruding your sides? Are you using a bevel cutter to cut nice clean 45 degree angles for the corners? Working with hard slabs presents its own set of challenges and getting to know the right time to do various steps. A couple of factors come into play for freeze/thaw issues -- water, I believe, expands about 9 percent when it freezes. You can minimize cracking of pots from freeze/thaw by not setting them directly on the ground where they would absorb water; putting feet on the bottom, setting them on tables, etc. will help. The more the clay body absorbs water, the more likely it will crack due to freeze/thaw dynamics. Adding grit or grog to a clay body may give you a more porous body -- and possibly a pot that is not vitrified when fired. More porous may give you that space within the pot that allows water to expand/contract during freezing/thawing, but it may also make your pot less water-tight as a planter. Study the designs of the bonsai potters you have checked out.

#10 mrcasey

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Posted 10 August 2013 - 12:24 AM

Bciskepottery - I’m rolling out slabs with a plain old wooden dowel rod. The corners are not beveled - they’re just butted. On a failed octagon pot, I tried beveling with a fettling knife and a straight edge. Let’s just say I need some practice.

You are so right about knowing when to work the slabs. I’m still not quite sure how hard I can/should let them get. I guess I’ll know when all the pot walls come apart in the kiln.  If I were working with wood, I could fix a lot of the edges I hate with a router.

 

Thanks for all the input and advice,

Casey

 

 



#11 weeble

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Posted 10 August 2013 - 01:55 AM

If you're looking for dark brown Laguna clays, out here we get the Western glazes and 'Brown'  and 'Electric Brown' both look great with bonsai pots.  I'm firing to cone 5 though, not sure they'd take cone 6.  You're going to just have to go ahead and work on construction, finding the right thickness and construction tricks like exactly HOW stiff the slab has to be to build the pot and still get good seams really IS a matter of experience.  I've used both to make bonsai pots, but mostly smaller stuff.  Larger pots I find Weststone II and some of the other groggy clays to be the best choice to avoid warpage.  Oxides and terra sigs can be used to change the color if you want unglazed looking pots.  

 

Bonsai pots are a tricky, futzy, ANNOYING construction exercise.  Drywall sheets for drying and proper slab rolling/handling are very important.  I'm finding 3/8" works, especially if I reinforce with a rim.

 

Patience, grasshoppah!

 

Edited to correct annoying lack of a grasp of fractions after an exhausting week.... 


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#12 Biglou13

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Posted 10 August 2013 - 05:14 AM

Mr Casey my original intent with pottery was to learn how to make bonsai pots. I found the strict design rules not to my liking and am making other things. I'm sure I will eventually return to make them again, but for now am enjoying looser forms. I now have an even greater respect for a good pot. Many of the japanese pots you probably have seen eg tokaname, are made with sometimes complex slump molds... So the ultra smooth and crisp lines are easier to achieve. Also if you really take time to,study and handle a pot you'll find that there are imperfections, often many. Often as potters/artists we are to focused on perfection or idea of perfection that we miss out on the beauty of object being worked on. Also more often than not what the potter sees a s flaws will not be noticed with a 75 year old trident maple is in it. Albeit a very important role in bonsai, the pot ultimately is a supporting role, a frame for the tree. Well the point I'm trying to get at is don't beat your self up over the small details. 1000 pots later you will definitely see progress.

Technique wise. To get that pro finished look, the surface is still workable until fired. So, smoothing, patching, slipping, rubbing, are your friends in green stage. Those pesky edges are still workable until fired. Even a little sanding in bisque stage. Straight is difficult with human hands, when at all possible use aids to make and tune straight and square surface. So like wood working you can use jigs and squares and straight edges to improve your surfaces. if you have wood working skills you can make custom tools. Just a personal opinion but in that size pot I'd like to see more drainage holes. Along with lots small pairs of tie down hole. Its hard to tell but I'm looking at proportion of foot to pot. Primarily height of foot. If you can find an old John naka bonsai books there is some great info in there about design ratio and proportion

That's a respectable pot!!. If you ever been to bonsai shows its usually 90% or better round pots. Because its difficult to make square ones. Can't wait to see it fired.
Caution big brother is watching.
The beige is blinding!!!!!!
The middle of the road is boring

The true sign of intelligence is not knowledge but imagination.
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#13 Mart

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Posted 10 August 2013 - 07:32 AM

I made one out of white stoneware clay and used iron oxide (F203) to darken the surface. It has wire and water/air holes at the bottom too. 26,5 cm wide.

IMG_2061-sml.jpg

 

Use clay in same temperature range you usually fire.

Have fun



#14 capt don

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Posted 10 August 2013 - 09:31 AM

Mart, that is an awesome outside texture, how did you achieve it?



#15 Mart

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Posted 10 August 2013 - 04:35 PM

Mart, that is an awesome outside texture, how did you achieve it?

 

Thank you :) I used same technique to make this horizontal vase: http://www.oostuudio...ga/img_2179_v1/

The surface of the clay is the key. I have to think about it how to describe the process of preparing the surface, so it actually makes sense.  :)

I'll take some pictures too and start a new thread. I invented it on my own (never seen nor read about it anywhere) It's a noisy business btw.



#16 weeble

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Posted 11 August 2013 - 02:25 AM

Ok, realized last night AFTER I turned this thing off, that 3/16 is SUPPOSED to be 3/8"....

 

A really interesting source for info on building bonsai pots is Lindsey Farr's World of Bonsai videos. ( http://bonsaifarm.tv/ )They have great info on how the Japanese pottery production town of Tokoname (which has many individual artists all producing pottery) does bonsai pots, as well as a few in China (I forget the name for the chinese ones!)  But it boils down to many of the pots, even the rectangular ones, are actually built by putting the slab into a mold, then reinforcing and smoothing the clay into the form.

 

All I can say is they've got the systems they use worked out, and there really are quite a number of different ways they build bonsai pots.


Maryjane Carlson

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