Well, I finally built my brick raku kiln and fired it up this past Saturday. I only fired four tea bowls but the main purpose was just to get the kiln built and learn about kiln design and the science of firing. No doublt I learned a lot, but I still have a lot of learning left.
I started with sixty hard fire brick, 10 soft insulating brick and about 50 red common brick. Inside dimensions were 13-1/2 inches wide and 16-1/2 inches tall. I had a small mouse hole that ran from front to back and 2 additional air holes on each side of the front of the kiln. For the roof I used a piece of 2-1/2 inch fiber board and used 4 soft brick to form a square exit flue in the back top portion of the kiln.
I was going to preheat the kiln with propane but found out at the last minute that both my propane tanks were empty so I started with a little bit of wood and some gas. I think I could have saved 3 hours of time had I preheated with propane. It takes a heck of a lot of time to heat those hard bricks and during this time, inbetween stoking, I decided to stack my red common brick around the outside of the kiln. This turned out to be a great idea as the exterior of this kiln, only one firebrick thick, became uncomfortably Hot. The second layer of brick really helped.
Another thing I learned was that a chimney really helps create draft and heat. Three hours into the firing I started to hear the slight roar of the fire. To see what would happen I stacked 3 more layers of brick on the chimney. Within minutes flame was jamming up and out of the chimney creating good draft and a nice roaring sound. I swear I could feel it as well as hear it. The addition of the chimney made it much easier to judge when to stoke more wood. When the flame and roar started to wane, it was time to add another piece of wood. You could actually determine when to stoke just by listening to the fire.
I also decided to experiment with a door in front of the stoke hole. I used a piece of broken kiln shelf. I learned quickly that seconday air holes are a must, but for this kiln a door is not neccessary.
I'm not sure if my mouse hole was designed properly as I frequently used a ram-rod and pushed it through the length of the kiln to keep air flowing through the embers. Will have to do some more research on that.
I used all kinds of different wood to fire this kiln. Some was cheap pine from wooden crates, some was old treated lumber from a deck, and some was a mix of good hardwood scraps from a cabinet shop. The wood was all cut into approximately 20 inch pieces and split into 1 to 2 inch widths. The kind of wood didn't seem to make much difference but the size did--the smaller width the better.
All in all it wa a good firing and a great learning experience. Got so fired up that I have stacked up another mini kiln of a different design. Need about 40 more brick to finish the chimney but hope to fire it this weekend. Stay tuned.
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