Firing Log

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.

Download the Eighth Firing Podcast directly or through iTunes (mp3, 56:45, 42mb).

Note: The iTunes link requires iTunes to be installed on your computer. If you do not have iTunes, use the “direct “link — it is probably most convenient to right click the link, choose “save as” from the context menu, and then listen to the file in your preferred player after it has downloaded.

I wrapped up my eighth anagama firing in the early hours of Dec. 23rd. The kiln is still sealed and I am (im)patiently waiting for Saturday to open it up. During the firing, I made some recordings of what I was doing or thinking. The purpose was twofold: 1) In the future, I will be able to listen to all my wrong thoughts — perhaps with a sense of nostalgia. 2) I knew that post-firing, I would need some kind of project to help me keep my grubby mitts off the kiln door. So far, the editing task has worked quite well, although I also built a light tent in the meantime for taking better pictures of pottery.

Some basic data points: I lit the gas burner around 9:00 pm on Dec. 17, started with the wood about 24 hours later, stopped firing about 10:30 pm on Dec. 22, and had the kiln sealed up by 1:50 am on Dec. 23. The kiln consumed about 3.5 cords of wood during the firing. From 5:00 am, Dec. 18 through 2:00 am, Dec 23, I slept 18 out of 117 hours.

I took only a few pictures during the firing, but they can be viewed in the photo album for the eighth firing. As for the pieces — I hope to open the kiln on Saturday. Till then, I’ll spend the time worrying and second guessing.