Firing Log

Fun first:

Here is a time lapse video showing roughly 90 minutes of stoking in two:
Nice quality, 65 mb, quicktime format.
Dreadful quality, 9.5 mb, quicktime format.

And of course, a photogallery of some of the work from the ninth anagama firing.

Now for the work:

My goodness, it’s been a long time since I posted. I finished up a firing at the end of March and then completely lost my motivation. I must have stoked the last of my energy into the kiln and honestly, I’m still waiting for it to come back — I’m burnt out. Even sitting down to write this entry is painful and I’ve been procrastinating for a month (!) despite the successful character of the last firing. I lament my lost motivation.

{… OK, let’s just do this …}

Overall, the ninth firing truly was good. I’m not 100% happy with the coloring or surface texture, but I’m satisfied for the most part. I received some nice pieces, had no shelf collapses, and internalized an important lesson. The firing can be summed up in three basic topics:

• I finally know exactly how to make the temperature climb like a rocket.
• However, I need to modify air inlet size, wood mixture, or both for brighter colors and
• I need to work on my closing procedures.

Stoking One Stick:

Furutani wrote that sometimes during a firing, the temperature of the kiln can be perfectly adjusted with a single piece of firewood. Even though I’ve read that line a dozen or more times, it was only in the last firing that I actually put it into practice. The effect was astounding and the technique eminently simple: stoke one piece of firewood, watch the chimney till the glow at its tip died, repeat.

The stoking cycle was about one smallish piece every two minutes. I don’t know what temperature I hit, but the light from the kiln was blinding. It was blinding even with sunglasses behind welding goggles. It was like staring at the sun; a sort of fear inducing “holy cow — my bricks are gonna melt” kind of hot. Hot enough that I could imagine the devil requesting my consulting services when things get cool down south.

In retrospect, it makes perfect sense — firing the kiln is an exercise in finding the perfect fuel/air mixture. Anyone who has read anything about combustive firings (no matter what the fuel is) has heard that it is hard to raise the temperature in a reduction environment. I know I’ve read that all over the place — Furtani, Olsen, and from probably a half dozen other writers. Sometimes though, reading is not the same as knowing. After directly observing the effect of hitting the fuel/air sweetspot, I finally “know” this fact viscerally. I won’t forget.

Brightening colors:

As for the color of the glaze, it is less bright than the seventh firing’s results — there was less orange and more brown in this last firing. Early in the firing, I held the kiln in a reduction environment to build up a carbon layer on the pots. While it gave me some interesting glaze lines, and effects, I think I prefer a cleaner brighter look.

The carbon effect shows up In this example:

View Photogallery

This piece appears to have collected carbon soot. When the glaze layer formed and liquified, it caused the soot to streak. Once the glaze built to a certain level, it seems to have flowed separately from the carbon layer, particularly on the neck. This effect works well with my notions of fire as water. It’s as if a winter rain partially cleaned a soot coated object before freezing into a glaze of ice.

While I think I might like this effect, it doesn’t change the fact that many of the pieces were mud-toned. By the same token, it usually takes me about 6 months or so to really evaluate whether I like something … except for those truly awful pieces which are almost immediately subjected to hammer justice.

Aside from carbon, another possible factor in the muddy colors was my fuel composition. In firings seven and eight, I used mostly softwood for fuel. In the last firing, I used a 50/50 mix of hard and soft woods. I think I’ll try bumping up the ratio to 25/75, hard/soft because it may be that the type of fuel has a stong effect on the reds.

As for why this difference may exist, I have no answer — only some guesses. It may simply be that hardwood is denser and thus one armload of alder and birch is the same as throwing in 1.3 armloads of fir. In that case, it would be a simple matter of too much carbon causing the darkening. Or it could be that the there is a different chemical reaction from soft wood flame than that from hard wood. I suppose a better test would be to continue with a 50/50 blend but stoke less when stoking hard woods. My gut is telling me to change the wood though … yet my gut is often wrong.

Closing Procedures:

One easily corrected mistake I made was in cooling the kiln. This mistake caused me much anguish for the week I waited for the kiln to cool. The answer is to use an alarm clock. Here’s the issue:
I like to have a glaze that is semi-matte with glossy areas. I am not so attracted to extremely dry glaze. A surefire way to build gloss is to quick cool the kiln. In the seventh firing, I quickly cooled for about 90 minutes. In the eighth, about one hour.

In the ninth firing, I decided to go for a full two hour quick cooling period. Around 1:00 am, I capped the chimney, closed off the lower air inlets, but left the stoking door wide open. I then struggled to stay awake for two hours at which time I closed the stoke door but did not immediately seal the kiln with clay slip. What I wanted to do was cool for another hour at a moderate pace to let the coal bed reduce itself, yet not drop the temperature so much that it was impossible for a certain amount of matte glaze would to form (matte glaze forms when crystals grow in the glass — a process requiring time).

To repeat, my plan was to wait one more hour, and then completely seal the kiln.

Six hours later I woke up in a panic!

As a result of the excessively quick cooling, the pottery is excessively glossy and there is very little matte glaze at all. This drastic cooling may also have played a role in the lack of any of the brighter orange tones. There is absolutely no orange on any piece I pull out during the firing, rather, those pieces that cool from kiln to ambient temperature in a 30 minute period are very glossy, but completely lack red or brown tones.

Anyway, for not using an alarm clock, I swore at myself for days.

Note: there is a photo album and podcast related to this entry.

I opened the anagama on Friday night (Dec. 29, 2006) after a cooling period a few hours shy of seven days. I had planned to wait until Saturday morning, but with visions of shizenyu dancing in my head, anticipation got the best of me and I unbricked the door about 15 hours early.

It was a difficult night however, and much unlike the seventh firing in which I pulled out many lovely pieces. Once I peeked into the kiln, my initial anticipation and excitement immediately gave way to despair and dismay, although several small finds allowed my spirits to rebound to some degree.

That which was right:

One idea that worked out wonderfully was “shielding”. By “shielding”, I mean setting up a wall of clay very near to a piece. In this way, the shield would absorb the ash and flame that would otherwise strike the front and melt into glaze. By making the shield incompletely cover the front, I hoped to have shizenyu mixed with hi iro (”fire color”). As this example shows, the result is wonderful:

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Sadly, I’m not that skilled with slabs so this vase separated at the seams. Still, with a little practice slab building, this technique could result in stunning pieces.

Here is a picture with the shield up — two notes: 1) I broke the shield trying to knock off a piece of stuck wadding, and 2) it was placed much closer to the piece during the actual firing than is shown in this picture:

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Another winner was this coil built bottle. I made an ad hoc shield out of wadding while loading. The shield wasn’t as close as the one on the brick shaped vase, and it only shielded the foot area, but it helped to some degree:

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One last pottery picture for the blog (see the photo album for more pictures) — the tube of this bottle was slab built and the base and cap thrown. It was plainly caught in a complicated eddy in the fire path:

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That which was wrong:

I’m very happy I recorded my firing. My general sleepiness makes memory of any firing rather fuzzy. This time however, I can hear myself making lousy decisions. The most embarrassing is probably my “olivine segment”.

Beware the midnight inspiration.

In a misplaced attempt to enhance green colors in the glaze, I induced a reduction environment toward the end of the firing. Lost in a haze of sleepy logic, I suddenly had the idea that olivine and reduction are related. I did no research, no real thinking — I just ran with the conclusion. Indeed, the wikipedia entry for olivine suggests that the green in olivine is not from reduced iron at all: “Olivine is usually named for its typically olive-green color (thought to be a result of traces of nickel), though it may alter to a reddish color from the oxidation of iron.”

Certainly a “red olivine” from oxidized iron, while not green of course, would be quite nice to have on the hi iro pieces. Besides, the glaze never has difficulty turning olive green wherever it is thick or puddles. Take my mistake as a warning, midnight inspirations should be examined in the light of day — do not simply “decide and do”.

Reduction is overrated … (probably).

It seems everyone talks about reduction but I’m seriously beginning to think that reduction is overrated. What did I get after making certain I wastefully pumped a metric ton of carbon through the kiln and out the chimney? A generous amount of muddy glaze with black halos in the transition areas (by “transition areas”, I mean the areas between the exposed-side and the protected-side).

I’ve tried firings that are more on the reduction side and firings that are more on the oxidation side of things. Not all the oxidation firings have been a success, but all the reduction firings have been either mostly or purely atrocious. Look at this picture from the third firing:

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After the pottery from the third firing was hammered down into small chunks, it made a decent aggregate when mixed with cement, but there are cheaper and easier ways to get gravel. There was absolutely nothing good about the third firing. In fact, my firings only began to improve once I began letting the kiln breathe.

Although not as disgusting as the third firing, the initial view from this firing brought flashbacks of horrid memories. My initial despair should be quite understandable:

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So in the end, while every talks about reduction environments, I think reduction does not fit with my preferences. I’m not saying it’s the wrong thing to do — just that I never like the results.

Lose the cones again.

Another thing I must do, is misplace the cones again. I think they lulled me into a false sense of completion. The cone packs I could see said the kiln was finished — cone 11 was laid flat. In the very back however, cone 10 never budged. The sight of a puddling cone 11 toward the middle-front of the kiln affected my judgment, even if subconsciously.

Plan for the ninth firing:

Quick cooling.

It sounds so counterintuitive — after spending days stoking the kiln to ever higher temperatures, does it really make sense to open up all the ports (air inlets and stoke hole), and allow cold outside air to flow freely through the kiln? The proof is in the finished product however. No firing was better (glaze-wise) than the sixth. At the end of the sixth firing, I left the kiln wide open for almost two hours. Had the shelves stood — it would have been amazing.

Although it is psychologically difficult to walk away and let the kiln breathe massive quantities of cold air, I will build up my resilience to this backwards-seeming idea. The ninth firing will feature a quick cooling period of at least one hour — longer if I can stand it.

Firewood.

Finally, I think I need to start using more alder again. In the last two firings, I have used fir almost exclusively. Fir is light and fast burning but its heat seems to have difficulty reaching the back of the kiln. Alder burns quickly like a softwood, but it is slightly denser and tends to hold temperature a little better. Secondly, because alder is denser, it has more “stuff” in it on a log-for-log basis compared to fir. In other words, one cord of alder should deposit more glaze making ash than one cord of fir. Between these two advantages, I’ll try to make my next firing based on alder, though trimmed with fir perhaps.

For now though, it’s time to begin preparing pieces for the next firing. After my initial shock, I’m now ready to move forward and eager to avoid the mistakes of the eighth firing. I especially want to experiment with slabs and methods of directing the flow of ash and flame.