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.|
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.|
|The arch is just underway in this shot. Note the arch form - and the saw - great tool for this job.|
|Ze bricks and all the dust are in the rear view mirror now!|
|Ceramic fiber is draped over the side walls and arch, 2" thick.|
|The side and top panels are in place, and the interior door is bricked in prior to installation of the outer door.|
|Rick welds one of the hinges on the outer door panel.|
|Rick is the man, I'm so lucky to have had him do this for me.|
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!|
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!