International Wood-Firing Exchange – some unfinished business


International Wood-Firing Exchange – some unfinished business
After arrival at the Osaka airport, it was only a matter of hours until we reached Shigaraki…Mr. Shiho Kanzaki driving Ginny Beamer and me up into the mountains, chased by a fiercely beautiful pink-orange sunset.  It was dark when we pulled into the kiln yard, a similar pink-orange glow highlighting bundles of wood, a small table, a clock, and the hulking shape of the kiln.  Karl Beamer was stoking, and had been in Japan for more than a month making enough works to fill Kanzaki sensei’s anagama.  The firing was already midway through the 10-day firing.  
“Karl san,” said Kanzaki, “you haven’t seen Ginny san for long days.  You go to the house with Ginny.  Dick san and I will take over the firing.”
And just like that, in less than 24 hours, I’d transitioned halfway around the world, from gray northern Indiana skies, to the fire-glow of a traditional Shigaraki anagama. Firing with Shiho Kanzaki, who at that time was to me, still, more hero than friend.  But our relationship was changing as well.
Over the course of the next few days of firing, and the eventual unloading, I made a series of observations and tentative conclusions about the long, hot Shigaraki firings.  The questions which those observations and conclusions addressed, I’ve carried with me for almost two decades.
Fuel:  Having been a wood-firer in the US, I’d wondered how it could take 10 days of firing to reach the kind of directional ash accumulation that I associated with Shigaraki pots.  
Each bundle of Japanese red pine wood was approximately 18 inches in diameter and about 24 inches tall.  The individual pieces were about half the size of the wood I was used to stoking. The per bundle price of $10 USD equivalence didn’t seem an unreasonable price for the fuel until I considered that it took a thousand bundles, over 10 days, to bring the firing to completion.
I’d assumed that Japanese red pine must be a similar species to American white pine, and as such, would have a generous output of green sticky, oozing ash flow.  Was it?  Did it?  I assumed so.
Clay:  I wondered if the Shigaraki clay, laden as it was with feldspathic contaminants, must be quite refractory.  How else could it endure long days of firing and have heavy ash accumulations only on the ‘front-facing’ sides of pots….and almost none on the non-facing side.  
Moreover, why else would Kanzaki a) fill only the front half of his anagama with pots and b) ’harvest’ only the front 50% of the pots from this firing – (moving the back 50% of the pots to the front for the next firing).  In actuality these finished goods of Kanzaki’s that I was seeing had all been fired twice…twenty days…two thousand bundles of wood.  
Surely the Shigaraki clay must be the clay equivalent of an industrial kiln shelf…of a composition that actually resisted the accumulation of wood ash.
In my own US wood-firing experience, in our relatively-short three-day firings, using mixed hardwoods and pine, always created significant natural-ash glaze-runs and drips.  Back sides of pots were ash-coated as well…not only the front-facing sides.  Even pots near the back of the kiln had rich natural-ash accumulation.  I wondered if this indicated that the clays I was using here in the US were much more receptive to wood-ash, than the refractory Shigaraki clay.
Firing:  I noticed that the amount of wood for each stoke, put into the Shigaraki kiln was smaller… less than I was used to using for each stoke.  In addition, the individual pieces were much smaller – nearly half the cross-section size as compared to what I was stoking in the US.  
And in broad estimates it seemed to me that the total amount of wood used in a 10-day Shigaraki firing was about twice the amount that I was used to burning in a US 3- or 4-day firing.
I noticed also that the amount of primary air allowed in the Shigaraki kiln was far less than I was used to employing.  
What were the relationships between the smaller fuel-piece size, the larger overall quantity of wood, less primary air, and a kiln filled only half-way?
Firing Temperature:  While firing the Kanzaki anagama, I saw colors at peak temperatures that I was sure I’d never seen before:  yellows and yellow-whites.  And the fierce radiant heat was something like I’d never felt before.  I had to assume that the Shigaraki kilns were being fired far hotter than I’d ever fired.  But how to know?  No cones were ever used in these Japanese /Shigaraki firings.  But based on my own lived experience, the temperatures seemed like they must be hotter.
So I left Japan with at least four theses: 1)  Japanese red pine is similar to American white pine in terms of the ash it gives up during the firing.  2)  Shigaraki clay must be far more refractory than the clays I was used to using….or that I’d seen used in the US.  3)  Shigaraki firings went to higher temperatures than did the American wood-firings that I’d been part of.  4)  An additional thesis was that higher temperatures were responsible for creating some of the soft pastel colors and hues that I saw in Shigaraki firings…the greens, pinks, blues, grays and purples.
Shut Down:  The final stoke of the Shigaraki anagama utilized a stoking amount that was at least triple the normal stoke amount.  And as soon as the final stoke was in inside the kiln it was ‘all-hands-on-deck’ to put a thick clay slop over every crack in the kiln through which glowing light could be seen, or wisps of smoke could come out.
In the US, I was used to making a final stoke of  only slightly more wood that would constitute a “normal” stoke.  Then I shut the kiln, and edged the chimney closed over a period of an hour or so, making sure that not too much black smoke and back pressure came from the kiln. I employed no sealing of the kiln with thick clay slop.
I wondered if the shut-down procedure had an impact on color development in the Shigaraki firings.
In an effort to test some of these theses, when I returned to the US, I decided to experiment.  Since Japanese clays and fuels were not available to me, I decided to address the variables that were available to me:  I fired hotter (cone 14 instead of cone 12), using smaller pieces of wood.   I tried a close-down procedure that more nearly matched the firing of the Shigaraki kiln – namely a final stoke of twice of three times the normal amount, followed by using clay slop to close up all the cracks in the kiln.   
To my surprise and pleasure, there was one very noticeable change in my US results:  The amount of pastel-hued results increased.
I attributed this to the higher temperatures, the larger final stoke, and the controlled shut-down, including the way I sealed the kiln at completion.
Remaining questions:
Several questions remained outside of my immediate ability to answer.
I really couldn’t know the ash-glaze-making properties of Japanese red pine without the help of an electron microscopy evaluation.  And I couldn’t know how hot the kilns were being fired without pyrometric cone comparisons.
None of my Japanese friends who work in the Shigaraki tradition use pyrometric cones.  And while I have electron microscopy results for most of the fuels I use (Chinese Elm, American Pine, Oak), I wasn’t prepared to import Japanese red pine and pay a lab to test it for me.
So I was left continuing to wonder about the fuels, clays and firing temperatures used in Shigaraki firings.  
Fortunately I am friends with Hiromi Matsukawa, the final independent apprentice of Shiho Kanzaki.  Hiromi works near Okayama (Bizen country), but has built a Shigaraki-style anagama, uses Shigaraki clay, and uses red pine as fuel.  He fires for 8-10 days, using approximately the same amount of fuel as the Shigaraki firings I’d participated in or observed.
I wondered about the possibility of a firing exchange.  What could I learn from having Hiromi make works from Shigaraki clay, bisque fire them, and send them to me for firing in my American 3-day wood firings using Chinese Elm fuel?  And what could be learned from sending my nepheline syenite-fluxed clay bodies to Japan to be fired in a traditional Shigaraki firing?  Fortunately Hiromi was game to try.  We’ve had about 4 firing exchanges to date.
My assumptions about the firing exchange:
I assumed that my “fluxy” clay bodies, fired for 10 days with Japanese red pine, would be absolutely awash with natural ash glaze.  I sent them with glued-on pot sitters, in anticipation of the massive glaze flow.
Hiromi’s work was made out of the (what I assumed to be a very “refractory”) Shigaraki clay body.  I would fire it in a three day firing, using Chinese Elm fuel.  Chinese Elm is high in potassium release and potassium begins to melt and flux at a very early temperature – 1100 degrees Fahrenheit.  Because of this early fluxing temperature, I assumed that my 3-day firing of the Shigaraki clay might create works that looked, roughly, like his 10-day firing.
The Results:
What I discovered was quite in opposition to what I expected.  My rather fluxed clay bodies, in his Japanese 10-day red pine firing,  were only barely ash-covered.  (In fact the results looked to me to be very much like the 20-hour firings that I used to do when I was first wood-firing….using scrap dimensional lumber that had no bark or cambium layer on the wood…..just barely blushing the works.)
Why?  My theses are beginning to change.  I’m beginning to question the ash-production of red pine.  I’m almost forced to assume that it is much less than I anticipated.  In addition, my works looked much “cooler” than I thought they’d look.  I wonder if Hiromi’s top temperature (since no cones were used) was more likely around cone 8 or 9…..and not cone 14 as I’d assumed.
Hiromi’s works in my firing:
Instead of being a refractory clay that resisted ash accumulation, Hiromi’s Shigaraki clay works were awash in ash, from a three-day Chinese Elm firing.  More than that, the clay seemed to be beginning to deteriorate.  The feldspathic contaminants surely melted.  A small guinomi of his had more than 20 holes in it, where the feldspar pebbles melted completely through.  The clay body slumped.  All the pots were  uniformly shiny and gray and gray-green, with little of the warmth I normally associate with Shigaraki clay.
I was so disappointed with the firing results of Hiromi’s clays, that I fired all the works, a second time, in a 3-day firing….this time using mixed hardwoods instead of Chinese Elm.  The results only worsened:  more melted holes, warping, and uninteresting colors on the surface.  I was more than embarrassed to return his works to him.  
Hiromi was willing to try again.  His second batch of works were fired in the Notre Dame anagama.  A 7-day firing, using mixed hardwoods that came from the Notre Dame campus. Firing temperatures were roughly cone 12-and a half.  These works were more like his Shigaraki-firing results, except all the back sides of pots were thoroughly glazed by the natural ash….no dry back sides, as one would normally expect in a Shigaraki firing.  
I too was willing to make a second attempt at sending works to Japan.  This time I sent only highly fluxed bodies.  (I’d expect shiny ash accumulations in only 24-36 hours using either Chinese Elm or mixed hardwoods.  But after 8 days of firing with Japanese red pine, these pots, too, were rather dry, one-sided, and lacking much variety, even though they were spread throughout the kiln, front to back.
Where this leaves me:  Conclusions and remaining questions:
I find myself facing the obvious:   it is not an easy comparison when mixing clays and fuel sources and firing-times from different settings halfway around the world from each other.  
I won’t ever know how hot Hiromi fires unless he begins using pyrometers and cones….which is unlikely.  He might be willing to put some cone packs in his firing if I sent them to him.  I’ll think about this.  For the moment, I’m assuming that Hiromi may fire to cooler temperatures that I normally fire.
I’ll never likely know the real ash-making qualities of Japanese red pine unless it can be subjected to election microscopy testing that would be similar to the testing results I already have on American fuels.  But for now I’m assuming that the ash-making capabilities of red pine, are less than the American species with which I normally fire (as evidenced by the Shigaraki clay I fired with American fuels).
And based on my firing experience of the Shigaraki clay, I’m now theorizing that it is likely not nearly as refractory as I originally assumed.
Final words (for now)……
There would be, of course, a more scientific way to approach my questions.  If budget were not an issue, a next step would be to both subject the Japanese Red Pine to electron microscopy analysis, and to import a firing’s worth of Red Pine and fire with it here in America, using my normal clays, firing approach, and cone-confirmation of temperatures.
Conversely, shipping a firing’s worth of mixed American hardwoods to Japan to be used as fuel in a “normal” Shigaraki firing would yield more information.
However at this stage of the process, I’m content to say that I’ve investigated my questions as deeply as I wish to.  There’s more to learn, but I’m not convinced that the learnings really yield affordable firing advantages.
It’s been fun.


Dick Lehman
18359 County Road 28
Goshen, IN  46528

About dicklehman

Potter, writer, educator. Available for offering pottery teaching workshops. Available for curating exhibitions.
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2 Responses to International Wood-Firing Exchange – some unfinished business

  1. Fred Hagen says:

    I see you are ever the student of wood firings
    and continue to marvel at your inquisitive
    mind and scientific approach to your work. I hope you’re able to conclude your experiment some day and can inform us all about the differences between your clay and your Japanese friend’s together with
    the different results between Chinese Elm and the Red Pine used in Japan.
    Keep on keeping on.

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