Firing Home Processed Clay

[JoeR]

Punch inon Google - Test Kiln/s
example -

http://www.clay-king.com/smallkilns.htm

Brother-in-law handbuilt one that looks like this -

http://aimkiln.com/photos/64jsmall2.JPG

Make it larger for bigger pottery but not neccessarily deeper.

All parts on Khai's kiln were second hand, as he also makes glazes from oxides etc. and the decomposition eats kanthal wire and bricks.
Will also run on a generator.
His house is now totally Solar powered, next wind generators.
Good Day
Anthony

So you're saying that all I need to make bonsai pots is a test kiln, bought or made, that reaches cone 6? Size wise I was thinking maybe 12×12×6 or 18×18×6.

I would prefer to handbuild it so I can make it just the size and shape I need it.

 

[iant]

I think kilns are cool but they are really just the finishing step. A lot of studios will fire outside people's stuff if there's space and not charge much for it. It would be even easier to do that if you were in a ceramics class. If you just want to make a kiln for fun and you have the space and the neighbors don't mind the fumes then go for it. But my advice is to see first if you like making your own work and if you're good enough at it so it doesn't crack when it's drying or fired. I'd work first on that stuff and then in the future you can get your own kiln. A single high fire kiln at a studio can fire the works of a few dozen artists. That's 1 kiln for a bunch of people.
I'd also suggest starting with good clay. It's dirt cheap. It would be very frustrating to use homemade stuff and spend a bunch of time on a pot and have it split in half during firing because of some organic matter in the clay.
http://www.leslieceramics.com/wp-content/uploads/2014/03/Clay-Price-List-2014.pdf

Ian

 

[rockm]

Good luck with this. You might want to look into your homeowners' insurance to see what's covered for fire and water damage. And you might want to look into buying two kilns since you're probably going to fuse all your work to the shelves in the first firing in the initial kiln.

Cone 6 probably isn't going to be high enough for Zone 7 use in the U.S.
http://ibonsaiclub.forumotion.com/t13998-is-cone-6-hot-enough

 

[JoeR]

I think kilns are cool but they are really just the finishing step. A lot of studios will fire outside people's stuff if there's space and not charge much for it. It would be even easier to do that if you were in a ceramics class. If you just want to make a kiln for fun and you have the space and the neighbors don't mind the fumes then go for it. But my advice is to see first if you like making your own work and if you're good enough at it so it doesn't crack when it's drying or fired. I'd work first on that stuff and then in the future you can get your own kiln. A single high fire kiln at a studio can fire the works of a few dozen artists. That's 1 kiln for a bunch of people.
I'd also suggest starting with good clay. It's dirt cheap. It would be very frustrating to use homemade stuff and spend a bunch of time on a pot and have it split in half during firing because of some organic matter in the clay.
http://www.leslieceramics.com/wp-content/uploads/2014/03/Clay-Price-List-2014.pdf

Ian

Oh yeah I use clay from some of the local pottery areas around me. I just wanted to make one pot out of refined clay in my yard for the sentimental value or the humorous aspect of it. Put a tree I dug out of my yard in it.

 

[rockm]

Good luck with this. You might want to look into your homeowners' insurance to see what's covered for fire and water damage. And you might want to look into buying two kilns since you're probably going to fuse all your work to the shelves in the first firing in the initial kiln.

Cone 6 probably isn't going to be high enough for Zone 7 use in the U.S.
http://ibonsaiclub.forumotion.com/t13998-is-cone-6-hot-enough

This guy used open source blueprints to build his kiln ;-)
http://www.langbonsai.com/kiln.htm

 

[mrcasey]

"Cone 6 probably isn't going to be high enough for Zone 7 use in the U.S."

I've seen this statement made before on bonsai nut and it's a bit of a red herring.
The comments made in the linked ibc thread (which I started) also don't seem to back up the assertion.

If the concern is frost resistance, the cone at which the clay body matures is not
the issure. The issue is vitrification and the amount of moisture absorbed by the body
after it's been fired to its proper cone. A cone 5 clay fired to 2185 F that absorbs 1.5% is
acctually more frost resistant than a cone 10 body fired to 2381 F that absorbs 4%.

The bonsai potter Chuck Iker fires his pots to cone 5 using cone 5 clay. He has a little blurb
on his website about moisture absorption and frost resistance. It looks like around 3% is
acceptable.

 

[JoeR]

"Cone 6 probably isn't going to be high enough for Zone 7 use in the U.S."

I've seen this statement made before on bonsai nut and it's a bit of a red herring.
The comments made in the linked ibc thread (which I started) also don't seem to back up the assertion.

If the concern is frost resistance, the cone at which the clay body matures is not
the issure. The issue is vitrification and the amount of moisture absorbed by the body
after it's been fired to its proper cone. A cone 5 clay fired to 2185 F that absorbs 1.5% is
acctually more frost resistant than a cone 10 body fired to 2381 F that absorbs 4%.

The bonsai potter Chuck Iker fires his pots to cone 5 using cone 5 clay. He has a little blurb
on his website about moisture absorption and frost resistance. It looks like around 3% is
acceptable.

Where on his website is that? I couldnt find it.

 

[JoeR]

It only frosts maybe 10-20 times a year but my luck after I make a bunch of pots we will get the coldest winter in NC history.

I was looking at buying 50lbs of white clay and maybe 50lbs of red clay, and this white clay has a 0.5% abs rate but is only cone 5. It also has a high shrinkage rate too but I can work around that,

http://www.bigceramicstore.com/laguna-clay-hagi-porcelain-clay-50.html

 

[rockm]

"Cone 6 probably isn't going to be high enough for Zone 7 use in the U.S."

I've seen this statement made before on bonsai nut and it's a bit of a red herring.
The comments made in the linked ibc thread (which I started) also don't seem to back up the assertion.

If the concern is frost resistance, the cone at which the clay body matures is not
the issure. The issue is vitrification and the amount of moisture absorbed by the body
after it's been fired to its proper cone. A cone 5 clay fired to 2185 F that absorbs 1.5% is
acctually more frost resistant than a cone 10 body fired to 2381 F that absorbs 4%.

The bonsai potter Chuck Iker fires his pots to cone 5 using cone 5 clay. He has a little blurb
on his website about moisture absorption and frost resistance. It looks like around 3% is
acceptable.

\

FWIW, I've seen lower fired pots disintegrate over a period of decades in repeated frosts here in Zone 7, including higher fired Chinese and a few U.S. craft potters. I've also found that pots fired over cone 8 are bullet proof and don't crack under heavy freezes. Lower fired pots do, especially if they've got overhangs or other design details. The results for lesser fired pots can be spotty. Some work, others don't. Over the last 20 years or so, I haven't had that happen with work form Ron Lang, Don Gould, Bryan Albright, or high end tokoname. I have had lower fired pots split up or delaminate or crumble in that period, however.

Bottom line, I would rather buy a pot that's bullet proof than buy two or three of the same lower fired pots as replacements.

 

[Anthony]

Pottery technology has advanced - vitreous - can be had at lower temperatures, depends on where you read.
Feels like I am in the Dark Ages.

Please look up the work of Richard Behrens and James Chappell on Amazon or a library.
Stoneware type bodies at 1100 deg.C [ cone 04 ] white / buff and red as well as Bone China.

http://www.amazon.com/Potters-Complete-Book-Clay-Glazes/dp/0823042030

http://www.amazon.com/Glaze-Project...71085&sr=1-1&keywords=richard+behrens+pottery

on our side we use a cone 08 [ 983 deg.C body ] vitreous
Good Day
Anthony

 

[mrcasey]

There was a thread on the IBC forums started by German potter Peter Krebs about frost resistant pots. In the thread,
Dale Cochoy, a guy with years and years of bonsai and bonsai pottery experience says that when living in an area that
freezes, you'll eventually have a broken pot here and there. Dale wrote:

I almost always at shows have someone ask when looking at my pots " Will this pot break in winter?" and it usually turns
into a longer answer than I'd like. I guess the best answer given for a high fired stoneware pot of good quality
clay is... " It shouldn't, but it might".

If I'm not mistaken, Dale fires to cone 10. There's no such thing as a "bullet proof" pot.


If there were issues with mid range stoneware frost resistance, I can't imagine that Chuck Iker wouldn't have gotten complaints or noticed his own pots breaking and therefore changed his clay body and firing temperature. While firing to cone 9 electric would be slightly more expensive, it wouldn't be any particular inconvenience and it just wouldn't make good business sense to sell substandard pots only to save a few dollars per firing. The problem, if it existed, would have been easily and cheaply fixable. The guy has been making and selling bonsai pots for at least 20 years.

Iker's faq: http://www.ikerbonsaipots.com/frequent-questions/

Here's what Iker has to say:

Are your pots frost proof?

Obviously this question is being asked by someone who’s experienced broken pots due to cold weather.
Let me address this in this way. My pots are all a stoneware clay body fired to 2185 degrees and have
a moisture absorption rate of 1% to 3%. A lot of low cost or imported pot are made with earthenware
and can have a 30% absorption rate or higher. They are essentially terra cotta. These easily crack and
spall when frozen because there is room between the clay particles for water to gather and expand.
The biggest cause of pot breakage is overly saturated soil in the pots. Expanding frozen water can bend metal.
A completely water filled frozen pot will crack regardless of the clay body. Pot shape and soil makeup also
play a role. A pot that tapers out toward the top can allow the freezing water to expand upwards thus reducing
the likelihood of cracking. Good soil drainage typical of a good Bonsai mix also helps. I have pots that taper
inward that have been outside in Ohio winters for years without breaking but they also have a good open soil
and are not allowed to fill up with water. A Bonsai planted in an ice cube is not good for the plant or the pot.

 

[JoeR]

This is what this whole discussion seems to say to me.

When talking about frost resistance, it is not dependant on the cone it is fired to but instead it comes down to the clays absorbtion rate. The real difference it seems is that cone ten pots may be able to handle say a fall off a bench better than cone six pots, assuming their abs is the same.

All these manor bonsai potters cant be wrong.

 

[rockm]

I don't know about vitreous clay absorption rates. I know that for the most part, lower fired pots tend to deteriorate in heavy freezes. I've seen it happen repeatedly over the long term. I have found that the "it's not the cone firing" argument tends to come from people in warmer growing zones.

As far as I have seen in the last 20 years since I began buying American stoneware bonsai pots, there are "bullet proof" pots. High fired Cochoy, Gould, and Lang pots haven't had problems. Pots from other American potters have.

Just saying, all things being equal, if there's a potter who fires to cone 10 sitting next to one that doesn't in a vendor area, I will tend to buy the higher fired stuff. Just me, though.

 

[DougB]

Joe have you checked with Jerry's Artarama of Raleigh. They are one of the oldest (1968) and largest art supply house in NC. And they carry a variety of clays, kilns, etc. And very knowledgeable folks who work there. Check them out.

 

[Anthony]

Actually a pot made from bonded fine sand can take a fall from 3 feet, 4 or 5 times before a crack appears.
My brother-in-law did the research for his sister's pottery shop back in the early 90's.

He started pottery around the age of 15/16 before he started Bonsai at around 17/18.
Lineage is Bernard Leach to Cecil-Archibald-Baugh to Ms.G,Harewood to him.
She also studied at Stoke on Trent in the UK [ memory for the name is week, could be Staffordshire - to lazy to Google - apologies ]

Vitreous is vitreous - and stoneware is normally 3 to 5 % water absorbent, earthenware is 8 % to ..................
Porcelain is or 0 to 3%.
Good Day
Anthony

 

[Anthony]

Two pots by brother-in-laws nephew Nick [ 18 in Jan.2015 ]
Handbuilt and fired in the afore mentioned test kiln.
Presently glazed with commercial stuff and has two trees.
Done as a gift to his uncle.

This is 4th or 5th effort. First ones were on a hand turned [ banding wheel ]
About 6" long, for both.

First body has grog, the second is normal.
Good Day
Anthony

 

[mrcasey]

"The real difference it seems is that cone ten pots may be able to handle say a
fall off a bench better than cone six pots, assuming their abs is the same."

This isn't particularly true either. Historically and in general, low fired earthenware
pots have been more fragile than stoneware. But to say that highfired stoneware is more
physically durable than mid fired stoneware isn't accurate.

While moisture absorption is one issue of strength, there are several other categories of
physical durability. These include but aren't limited to tendency to chip, crack, crumble,
or otherwise succumb to pressure. There is also the huge issue of glaze fit. Glaze
defects and poor glaze fit can considerably weaken a pot.

About 15 years ago, the great teacher and ceramic artist Professor Pete Pinnell did an informal
experiment on clay body strength. Pinnell and some of his students mixed up batches of 50
clay bodies of various earthenware, low through high fired stoneware, and porcelains.
To Pinnell's great surprise, he found that a particular low fired red art based earthenware was stronger than
any of the other 49 bodies. It was fired to maturity at a full cone 04. That's 04 not 4, mind you.
I'm not suggesting that you use earthenware as it would most likely absorb way to much water at maturity.
Also, most earthenware isn't that strong. I'm saying that you have to look at the body on a case by case basis.

I once considered using porcelain for my bonsai pots because I noticed that moisture absorption drops
almost to 0%. I figured it was the perfect body and would never succumb to frost damage. That may
be true, but I learned from some other potters that the density of porcelain can make it brittle
and susceptible to chipping.

Now after all that I must say that if I had a choice, I would probably fire cone 10 reduction.
I love the look of fly ash and salt glazes. I love the look of those traditional Asian glazes like shino,
temmoku, celadon, etc. Also love the look of an unglazed wood fired pot a la Ron Lang.