Category Archives: glazes

And so it begins…

Two years ago, my supply of stable dobai 土灰 dried up. I bought up the remaining stock from the supplier, but that didn’t last long. When I switched to another source of dobai, the results were far different than what I had imagined. My two main bread and butter glazes haven’t been the same since.

Which brings me to my current predicament of having to basically start from zero and re-formulate these glazes with different ash. Fortunately, I have basic analysis info from the old ash, and also for the new types I will be testing with, so I can use glaze calculation software to calculate substitutions, which I am hoping will give me a head start.

For your daily dose of trivia, the word dobai is rendered in kanji as tsuchi 土, and hai 灰, or  ‘dirt ash’ (which makes no sense to me). All other ash has a proper name, like pine ash, oak ash, fern ash, etc… I finally found a possible explanation for this odd name the other day when I was searching for ash sources on the net. Turns out the ‘do’ of dobai is actually shortened from the original name ‘kamado’, which is a large pot used for roasting, cooking, burning stuff, etc. It is easier to say dobai, than kamadobai, after all, I guess…

Here are my 3 main candidates for testing:

WD_7EA2I picked up one kg of each, and will narrow it down to just one. They are all about 10 dollars/kg, expensive right?  I make my own pine ash because I have a good source of already burned pine, but I’m not set up to process large amounts of ash, and when it is all said and done, spending 10 dollars or more per kg is cheaper than the time and sweat put into making my own ash. Rice straw ash is more expensive at almost 20 dollars per kg and it is still worth it when you take into consideration the gathering, burning, quenching, floating, stamp milling, 2nd floating, (ball milling in some cases), and drying process this ash requires.

Chawan for Japanese Tea Ceremony

I am making the distinction, because this last trip to Korea and the tea bowl festival really accented the differences between the preferred shape of a tea bowl between cultures.

The one type of bowl here that probably illustrates the point best, but of which I don’t have a good example, are the Ido chawan. We make these forms in Karatsu, but don’t refer to them as Ido Chawan. Rather, we call them Karatsu Ido, or Ido Gata Chawan. The original Ido Chawan are from Korea, and contrary to the idea that the ideal shape is like Kizaemon (below), Ido come in many shapes and sizes. I’ve even seen on Ido bowl with a warikodai (foot carved into sections).

Kizaemon Ido
Kizaemon Ido
Karatsu Ido, Nakazato Shigetoshi
Karatsu Ido, Nakazato Shigetoshi

Anyway, if you look carefully at Ido forms, two things are often noticed: One, the lip is quite sharp on the inside edge, even though the outside of the edge is rounded, and two, the interior of the bowl is not rounded but rather pointed. These characteristics seem unrelated or even impractical for tea, after all, who wants a lip that is less durable, wouldn’t a round lip be more practical? Also, a cone shaped pointed interior is not suitable for whisking tea, is it? There is no room for the whisk to move, after all.

So why did tea masters choose these bowls as paragons of ‘teabowlness’?  The answer is simple. They weren’t used for whisked tea. Most tea practice revolves around usucha, or whisked thin tea, but the tea that holds the highest position in tea ceremony as an indispensible part of Chaji,  the full tea ceremony, is koicha, or thick tea. Thick tea is not whisked, it is kneaded and folded slowly into a thick paste with the whisk, and the coned interior of the bowl allows for this to happen much better than a flat or rounded interior. Then when drinking this thick paste, it is much better to have a sharp interior lip in order have a clean separation from the bowl when drinking. Koicha is usually a shared bowl, and will be shared by two or more people. After drinking, you must wipe the lip and pass it along to the next person. The sharper interior lip makes both drinking and wiping an easier less messy experience. So, these two characteristics end up being optimal for tea, in the proper context of Japanese koicha.

Even more interestingly, these two characteristics were not intentionally designed by the makers with koicha in mind. They are the direct result of the clay, process, and tools used to make the bowls, which were likely made quickly in large numbers.

In Karatsu, we use cows tongue ribs to shape the clay, because it is large particle material and not very plastic. In some cases, such as porcelain stone and sandstone, it is not even clay at all. The cows tongue allows shaping by compressing the clay body, rather than stretching, like a standard rib would do. I always thought that cows tongue ribs came from Korea, but I have never seen one there during my visits. There is, however, a tool that looks a little like a mini tugboat that functions much the same way as a cows tongue. When making bowls quickly with as little wasted movement as possible, the interior of the bowl naturally becomes conical rather than rounded, and pressing the lip between finger and cows tongue naturally produces the characteristic Ido lip shape, while preventing splitting of the lip by compressing the  un-plastic clay body, and also eliminates the need to use a chamois on the lip to compress or clean up.

So, I seem to have gotten off on a bit of a tangent here, but back to the  main goal of simply leaving you with some images of tea bowls:

 

E Karatsu chawan, Mike Martino
E Karatsu chawan, Mike Martino




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Chosen Karatsu Tsutsu Chawan, Mike Martino
Chosen Karatsu Tsutsu Chawan, Mike Martino

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Kawakujira Chawan, Mike Martino
Kawakujira Chawan, Mike Martino

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Kawakujira Chawan, Mike Martino
Kawakujira Chawan, Mike Martino

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Chosen Karatsu Chawan, Mike Martino
Chosen Karatsu Chawan, Mike Martino

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Chosen Karatsu Yohen Chawan, Mike Martino
Chosen Karatsu Yohen Chawan, Mike Martino

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Kuro Karatsu Chawan, Mike Martino
Kuro Karatsu Chawan, Mike Martino

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Chosen Karatsu Katakuchi Chawan, Mike Martino
Chosen Karatsu Katakuchi Chawan, Mike Martino

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Processing Clay and Ash

In a recent massive cleaning around and in the studio, I changed things around to utilize some of the outside space more efficiently. One of the most important things is that I now, again, have a setup for processing clay and ash that I have collected and burned.

I had been getting close to finishing off my stores of collected clay that I processed some years back, time to start doing it again. I think I have a better system this time, and I have an inexhaustible supply of pine ash for now, too.

I have buckets, bags, and jars full of old collected clay and dry trimmings that need recycling. It should take some months to get it all blunged and pugged.

Collected clay that has literally been sitting around for years.
Collected clay that has literally been sitting around for years.

The Choppage ‘cho’ ‘pah’ gay’, is a traditional Korean tool for scooping off clay and other materials without disturbing everything underneath. It works much better than a ladle. I couldn’t find anyone who made them anymore, but my mentor still had one which is kindly letting me borrow.

Clay washing bucket setup, and scooping tool, called choppage.
Clay washing bucket setup, and scooping tool, called choppage.

I just agitate the material in the bottom bucket, wait, and scoop off the stuff that settles last.
Then, later after it settles in the upper bucket, I siphon the water back down into the main bucket. When enough of the upper bucket fills with material, I dump it into cloth lined basket or plaster to get out the excess water.

After returning water back into the main bucket from the 'good stuff' bucket.
After returning water back into the main bucket from the ‘good stuff’ bucket.

With the ash, the process is the same, but after I get out the good fine ash I transfer it into another bucket and wash it some more to get out the nasties. The nasties cause problems with glazing sometimes and I don’t like them. I do save the water containing the nasties for other uses.

Pine ash bucket setup, main on bottom, fine up top.
Pine ash bucket setup, main on bottom, fine up top.

The leftover rough ash stuff seems like a waste to just throw away, so I am thinking about ball milling it to see if it can be useful in some other way. We’ll see…

The leftovers after the good stuff is scooped off.
The leftovers after the good stuff is scooped off.

 

Scooping with the choppage tool.
Scooping with the choppage tool.

The sieve is 120 mesh, because I lucked into a cheap recycled sieve. I would usually use 100 mesh, so it is not much of a difference.

Dumping through sieve which is sitting on the bucket mouth.
Dumping through sieve which is sitting on the bucket mouth.

8th Wood Firing Photo Record

This post is a photo record with comments, in order to organize and retain my thoughts and observations about the 8th firing of the wood kiln. I always think I’ll remember until the next firing, but never do. So, if you get into this, beware there are a LOT of pictures, some of which may seem redundant. There are examples of most of the pots from the firing, minus teabowls and some others which are not photographed yet.

The 8th firing was a charm overall, with many good pots, some bad, and some that will get refired. Kiln was fired in oxidation primarily. We stoked once every 30 minutes for 2 1/2 days, then once every 20 minutes the last half day.

– Front was nicely melted, nice even gradient to the rear of first chamber, E-Karatsu was about ideal. Cone 12 at hottest front down to cone 6 at coolest rear.

– Front chamber behaves like anagama. No significant temp gradient from front to back of each setting. Next firing, will pack kiln by eliminating the space between settings, leaving horizontal space for flame travel. One long setting from front to back of first chamber.

– Ame yu better at low temps. Load rear to mid chamber.

– Ao yu needs more heat, mid to front chamber.

– Large platters go midway to back of front chamber. Too much ash up front.

– Firebox wares are very nice in a three day firing. Great place for Shino, under cover to avoid ash in pots.

– Rear chamber fires fast when preheated for 3 days. Jumped from 1044C to 1344C in four stokes, a little over an hour. Care must be taken to spend more time soaking at high temp, because rear chamber high temp wares not quite mature (surface changes only), clay not melted well. Spend 3 or 4 hours firing off rear chamber, slowly, to get inside the pots.

– Rear chamber fires very evenly front to back, and top to bottom. Pick a temp to fire at and load accordingly. Don’t expect a significant gradient.

 

Postfire thoughts

Well, time to sit down with the last firing and figure out what went wrong, and what went right.

Firing and packing: Great. With this firing I figured out, FINALLY, the proper exit flue volume to use. And with it, the proper packing procedure. The kiln climbed steadily, without effort, for 45 hours and the flame in the front chamber reached front to back really nicely. It turned out to be a fairly even gradient from front to back, from cone 13 in front, to a good melted 8 in back. No sidestoking necessary.
I am going to go back to using a pyrometer for the next firing, because this firing got very reduced. I think the stoke intervals were too close, and a pyrometer may help me get a better idea of temp climb timing, and when each cycle goes into oxidation.
At one point, when we switched to stoking the 2nd chamber, the temp just started dropping. You could tell from the sound and color of the kiln. I jabbed a pyro into a peep hole and it told me right away that I was stoking to frequently. After the flame had receded into the chimney and peepholes, and the roar had died away was when the temp really started climbing in the chamber. I had been stoking when the flames receded and the kiln quieted down, but once I started waiting rather for the temp to start dropping after the rise, the kiln got back on track. This rise took longer than I imagined, sometimes up to 10 minutes. Had been stoking waaayyyyyy too much.
This firing was a watershed moment for me, regarding packing, air, and stoking. I think next time will finally be the load that makes us all smile.

Glazes: Glazed ware in the second chamber turned out really nice. Reduction was still too heavy, but we got nice surfaces. Still, I won’t aim for that in the future. Madara glazes were too yellow for my taste. The first chamber glazes were so reduced that whatever their intended color, everything turned out a semi matte green, from the excessive iron pulled from the body saturating the glaze and crystallizing. I think the stoking interval will fix this problem.

Clay body: Oops. Here is where the shit hit the fan. Too much iron, especially considering the temp and amount of reduction that happened. The clay I used for the large pieces has too much iron for that type of firing environment, which is why they almost all collapsed. Having worked with a gas kiln for so long, it is hard to get out of the mindset of adding iron rich clay to other whiter bodies in order to get a desired color. The white clays in this area have enough iron for good color in a wood kiln. I keep forgetting that, but perhaps the shock of this latest meltdown, and the subsequent pain of shelf grinding will serve to jog my memory whenever I’m mixing clay for the wood kiln.

We got this off the shelf in one piece! The attached cup sits level when you set the piece on a table, so great for sashimi and  sauce or condiments.
We got this off the shelf in one piece! The attached cup sits level when you set the piece on a table, so great for sashimi and sauce or condiments.
The Fall of Icarus
The Fall of Icarus
Arm detail
Arm detail

At long last…

… some pictures of new fired/finished work. Finally got my brightness and white balance issues resolved and took a few pictures to share with everyone.

I hope you enjoy them…