Wednesday, August 27, 2014

What I did this summer

Samos, Greece
So this summer has been a bit of a blur, really. I've got to stop doing these crazy summers and take some time out to relax. Next year!

Summer started out a tad early for me this year as we had a family gathering on the Greek island of Samos in late May and early June. Upon my return, I started on rebuilding the kiln.

I'd like to start out by giving some background on the kiln itself.

I built the first version of my kiln way back in 1995. Everything in it, except the steel braces (which I bought new), was used. Actually extremely used. I got a good deal  - "any of those bricks in that pile there are 10 cents each" was what Mike said when I asked if he had any used bricks behind the studio and gallery at the old Blue Spruce Gallery here in Bend. I think at the time a new brick cost upwards of two bucks apiece so that was good incentive. The problem was that there were very few bricks that were full bricks. Most of them were parts of bricks, and the kiln had quite the jigsaw puzzle appearance once I had used them in the kiln. I also snagged a door for a hundred bucks or so from Mike and actually have been using that door up until a few months ago. I've never been so happy to take something to the metal recyclers, that door was huge, unwieldy, and not a very good insulator by the time I got it. But, funky as that kiln was, it worked, though not without adventure.

When we moved to our current location in 1998, I rebuilt the kiln with all new bricks. And, just last summer I did a quick rebuild in order to replace the arch which was at the end of its useable life.

This past February Hank Murrow was here with Inayoshi Osamu. Hank, being the builder of some 120 kilns over the years, was asked by me for a critique of my kiln. I knew the design of my kiln was not the best in terms of insulation (resulting in long firing times and using a lot of fuel to reach the final temperature) but I did not know what I could do to rectify the situation. Hank had several suggestions, the two biggies being that the chimney was not mortared and therefore letting a lot of outside air in between the seams where the bricks met each other, and that I should add extra insulation on to the outside of the kiln and place a membrane over the insulation.
So, armed with a plan, I started on the kiln project.

Here's what the old kiln looked like:

That's the door I sort of didn't like so much. Ok, I hated it. I admit it.

Closer view of the gaps between the bricks in the chimney.
You will note that the burners are not in place in any of the photos except for the very last one way down there at the bottom. I have gotten in the habit of removing the burners and storing them in my studio between each firing to avoid them rusting. Plus, I did not want to be tripping over them while I did the rebuild.

Here's a shot of the kiln which has been torn down to the floor:

The iron frame is left in place, everything else is pulled, inspected for replacement or re-use.
As the new kiln takes shape, I am re-using many of the soft k23 bricks that have been in the kiln but are still in great shape. Any bad ones are replaced with new bricks. I would like this kiln to last for the next ten years or more, and as I was unable to really work at my usual pace, I really took the time to do everything to the very best of my abilities. It was really a boon that I did not have a production deadline until the end of August, so I was not feeling pressured for time. Eventually, of course I would feel very pressured for time, as the final stages to finish the kiln hit some snags and the project was fully completed three days before I had to fire it to meet my commitment to orders. Talk about an uptight potter. Yikes!
The arch is just underway in this shot. Note the arch form - and the saw - great tool for this job.
In the photo below, the brick work is pretty much done. I've dealt with the leaky chimney by installing a metal sleeve over the bricks, you can see it behind the kiln. At this point the kiln, the three previous times that I have built it, would have been considered to finished. The problem with the design, however, is that there are only 4-1/2 inches of brick for insulation. Most high fire kilns have a 9 inch thick wall. While a kiln with thin brick walls still works, but it takes longer to fire and costs more money to reach the temperatures required for cone 10 wares.
Ze bricks and all the dust are in the rear view mirror now!
Now the new, fun phase begins...insulating the outside of the kiln! For the side walls and arch, I've elected to use 1" thick ceramic fiber, and to add two layers so I have 2" of insulation. Even though it is thinner than brick, the fiber will provide at least as much insulation as a 4-1/2" brick.
Ceramic fiber is draped over the side walls and arch, 2" thick.
Once the fiber is in place, I covered it with sheet metal panels. This is important as the dust that comes off of the ceramic fiber is very unhealthy to breathe.
The side and top panels are in place, and the interior door is bricked in prior to installation of the outer door.
At last, it is installation day for the front panels! Rick Vecqueray from ThreeSixNine Metal Fabricators shows up with the panels and his welder. Inside these panels is 2" thick ceramic board which is also installed on the back wall of the kiln. Sparks will fly this day! Rick designed an upper door that is mounted on hinges to the kiln frame and swings upwards to open, with a latch that holds it in place while I load and unload the kiln. The lower frame is manually lifted into place and everything is held by brackets and a great latch system.
Rick welds one of the hinges on the outer door panel.
Some hours later the man behind the welding mask emerges (Rick) and the job is done!
Rick is the man, I'm so lucky to have had him do this for me.
I felt like I was in a dream during the first firing as it went so well. The firing was completed in 12 hours, compared to the normal 16-20 hours it routinely took to fire the old, under-insulated kiln. And, I used approximately one third less gas during the firing. I'm quite sure my gas bill has been cut in half. And as an added bonus, I was able to get to bed at a super reasonable hour after the firing, instead of having to kiln sit through the night and in so doing, compromise the quality and quantity of sleep when I did get it.
In the photo below, the burners are lit and the kiln is just starting to glow at the burner ports.
First firing is under way!
So. There it is. What I did this summer. I thought this project would take two weeks, and it took six. But I told myself as I was working on it, seemingly endlessly, that I would thank myself for doing all the work that I did. And after the first firing, I can say it was well worth the effort, and that I'm extremely proud of how it came out.

With thanks to Hank Murrow for his generosity in advising me with answers to many questions I tossed his way. And I'd like to suggest Fred Olson's Kiln Book (I have the first edition and there is an updated version now available) and also Mel Jacobson's fantastic book, 21st Century Kilns. (Mel's book is super!!)

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UPDATE January 2015--There is a major flaw in my kiln project. The flaw is that I put insulation over the top of the steel frame. My understanding of what happens with extra insulation is that heat travels outwards through the insulating fire bricks and into the fiber and fiber boards. If there is steel in between the two layers, it will get exposed to excessive heat that can ultimately cause the steel to fail. Many, many thanks to Vince Pitelka for bringing this to my attention - and also scaring the shit out of me at the same time...god knows what could have happened if the frame failed during a firing. The minimum would be damaged furniture and wares in the kiln, the maximum would be a fire that could have burned down my house. I can be somewhat of a catastrophic thinker, but I don't think my imagination has gotten too far out of whack in thinking of what could happen with a frame collapse at cone 10 temperatures in the 2300F degree range. Holy shit!

What I have to do now is take off the sheet metal panels and remove any insulation that is over top of the steel frame. I have fired the kiln four times since the summer, and I have my fingers crossed that there is minimal damage to the frame.

By the way, the way I found out that I had a potential disaster on my hands was from a recent thread on Clayart. Someone posted a message wondering if they could add an extra layer of insulation on the outside of their electric kiln, and responses came in saying that the metal jacket that holds the bricks in place would disintegrate in time if it was sandwiched between layers of brick and insulation. So I started e-mailing respected kiln builders to find out if this would be an issue with my kiln, and started getting really frightened by the responses. Thankfully it is an easy fix, and very likely no harm has been done to the frame. I am so glad that part of my daily reading is the Clayart group, and I encourage you to get the e-mail digest sent to your inbox each day.

I blame myself entirely for this oversight. I didn't know enough to ask about it specifically, and Hank probably presumed that I was not a moron and would have known about this kiln building no-no. Anyways, as a result I have learned a very valuable lesson about thermal dynamics. I don't know about you but I seem to have a knack for learning things the hard way :)

Pottery is unforgiving. In order to get a successful pot out of the glaze kiln, you have to perform a multitude of tasks, each one performed with utmost attention and skill. One mis-step along the way, and your pot is compromised. So it is too, with kiln building. One tiny little oversight can be catastrophic. So, I continue to learn and to thank all those who have taken the time to help me. And, in turn, I take time to help those who ask me questions.  I think most potters are generous this way, and more knowledge is to the benefit of all!