Thursday, March 18, 2010
Here are photos of some of the pots from the first firing of my new kiln.
Fueled by propane, most of the glazes appear much different than from my old kiln.
One reason would be the reduction atmosphere was greatly increased. While back-pressure could be observed from the top & middle peep holes during the firing, how much reduction is only relative to previous observations.
The set of nested bowls in the last pic is a good example: The glaze inside the bowls has 3% copper that usually comes out of a fire appearing celadon-colored, sometimes splashed red or violet. This time it came out blue. I'm not complaining at all, but I was very surprised.
The bowl directly above it was a re-fire, of a black & white bowl that was not interesting at all. In the increased reduction atmosphere, the colors have flowed & copper migrated into a beautiful result. (In my opinion.)
There was only one bowl whose glaze ran onto a shelf. Although there were a number of pots that were under-fired, they can be re-fired a later time. It was strange to see pots with under-fired glaze on the same shelf as those with mature glazes - even the same glaze.
Howard & I had much discussion as each shelf was unloaded. His opinion of the result & my observation of what I expected. We made significant change to the design of the bag wall.
The next firing will be mostly wood-fueled, and with the bag wall change, should result in a much more even firing.
This firing had to go slow to dry out the mortar & bricks, check the bag wall design, and check for any major air leaks. I am very pleased with the results and the kiln.
I look forward to the next firing - the first wood-fueled firing of my new kiln.
There is much wood-splitting & stacking to be done. I absolutely have to get a handle on how much wood it will take to fire this kiln. Stay tuned....
Tuesday, March 16, 2010
The kiln took quite a few days to cool, as hard bricks hold heat a long time.
Firing was on Wednesday, Thursday everything was still very hot. Fri, Sat & Sunday, I worked at the winery. (I have a part-time job at a winery tasting room/art gallery just 3 miles down the road from me.)
Each day, I opened the kiln a little more. Friday, it was cracking the dampers and removing kaowool from the burner openings. I also removed the door frame of 2" thick kaowool that super-insulated the bricked-up door. Saturday morning, I checked the temperature inside the kiln with the pyrometer, and found it was down to 700 degrees F. I could safely remove the 3 peep hole plugs on the front & back for a final cooling. It wouldn't be until Monday that I had time to take down the brick door. Monday was a beautiful, warm, sunny day - very different from the intense cold and showers of the previous week. I had to wait til dusk to take the photo you see on the above left, as the sunlight across the bottom half of the kiln washed any picture-taking with my digital camera.
The piece on the right was contributed by my friend Bob. He brought over a half dozen pieces that he sprayed an ash glaze on. The ones I have seen turned out great. What was that glaze recipe again? I'd like to use it on more pieces, next firing.
In the meantime, on the day the kiln was fired, I caught a nasty headcold that is still hanging on a week later. I also got a (fortunately, very mild) case of poison oak on my face and neck. During one of the lulls on firing-the-kiln-day, I decided to get my electric chain saw out & start cutting some of the branches from the wood pile near the kiln. I remember using a gloved hand to turn up the collar on my down vest, and wipe my running nose. Will I ever learn to not touch my body after touching oak rounds? I did toss a few small pieces of wood into the firing kiln, but we decided the wood was not dry enough to make any contribution, so it got re-covered for the next firing. Never a dull moment.
Howard is due here tomorrow, Wednesday, to show me how to remove the delicate thermocouples from the burners until the next firing. Perhaps I'll get the first stack of shelves unloaded so we can see the middle stack of pots and draw conclusions from the first firing.
So far, I've seen there was very good reduction in the kiln, the colors are incredible. To my surprise, the colors turned out different than they used to in my old kiln. I will photograph & post these soon. The inside of the kiln is beautiful! The hard bricks are a toasty brown. You can see a large vase in the upper left of the front stack. It was in the kiln as a place-holder, a cracked piece of stoneware that I kept around just because I always liked the shape. It turned out a beautiful light brown. I'm pleased with the pots I've been able to see, and look forward to the others.
All the anticipation & preparation for this - and it is finally happening.
I could barely contain myself. I worked long days glazing and loading the kiln, preparing for Howard to come over and set the burners so we could finally light the fire.
While I bricked up the door, first with hard bricks facing the inside of the kiln, then with soft bricks backing up, Howard set the burners. If you look closely at the middle photo, you can see a thin wire behind (to the right) the burner, which attaches to a thermocouple that rests next to the hot end of the burner (in the far left photo, it peeks through a hole in a side "arm" of the burner. The thermocouple is a safety, that needs to "sense" the flame coming from the burner. If anything ( say, a gust of air) were to blow the burner out, the thermocouple stops the flow of propane. Thus preventing a build-up of highly flammable gas.
After lighting the burners, it took a while to keep the flame very low, yet still lit. We needed to slowly dry out the mortar in the kiln. The weather had been cool and damp all winter, and a lot of moisture had accumulated in the bricks. This was the plan for overnight. A storm was blowing in, and an old door was moved in front of the burner as a windbreak. The burner on the opposite side was safe from incoming breezes.
Once all was set, Howard's partner Deborah, surprised me with a picnic & bottle of wine to "launch the kiln". We toasted the first firing.
I checked the kiln overnight, all was fine, no burners had been blown out. Early the next morning, I slowly turned up the gas. We kept the firing slow as the kiln was steaming heavily. Howard didn't come over until late morning. He wanted to be on hand as we took on the challenge of getting to desired temperature from top-to-bottom and side-to-side.
The photo on the far left is looking through the kiln from one burner hole to the other. When the gas is turned up, it is quite a view to be able to see the glow emitted from the maw of a burner.
On the right-side photo are me & Howard, the kiln guru.
It was a long day and evening, as Howard & I discussed whys & wherefores of kilns and firing. And why I wanted the dampers in, so my glazes would come out as I desired, even though it took much longer to fire that way. About 9:30pm, as the both of us were physically & mentally exhausted we decided the firing was done. Cone 10 was "touching down" in the middle of the back side. Not wanting to over-fire (under-fired pots can always be re-fired, but once they are too hot, it is too late for the pots) the middle of the kiln a usual hot spot, we shut down.
Friday, March 12, 2010
First pic shows the bag wall design. The bottom 2 rows of the bag wall are mortared in. I kept the vertical bricks & horizontals above loose for this firing, so I can adjust for the next firing if desired.
Half bricks were used under the bottom shelves, to give a 4.5" rise off the kiln floor.
Cone packs, that indicate how hot the kiln gets at a particular site in the kiln, were in front of each of the 6 peep holes, and an additional dozen were scattered around the kiln, including the floor and bagwall.
The next 3 photos are the back, middle & front stacks of shelves.
I had mis-judged just how much larger this kiln is than my last kiln.
A friend had brought over some pots a few days previous to add to this firing. I still ended up bringing some pots from the "archives" to be re-fired, in an effort to fire a full kiln.
One thing I didn't discover until I was stacking the front shelves was this: Since I had to turn the kiln shelves sideways to get them through the doorway, there was a limit as to how high I could put the top shelf in front. I will have to make sure I have at least a kiln shelf of taller pieces for every kiln load fired.
Tuesday, March 9, 2010
These are some of the last preparations before loading pots into the kiln:
Right pic is 2" of kaowool over the arch and on the door frame.
I had planned on tying porcelain buttons onto the door with nichrome wire, but found that by cutting the kaowool 1/2" wider than needed, it just eases into the frame and stays there with pressure.
If you look carefully at the left pic, you can see the dampers in horizontal position.
There is one on each side of the chimney, and they are stark white.
I had a mullite electric kiln shelf cut into pieces that would fit the damper openings.
Next post will show loading the kiln.
The firing is so close, I can taste it.
I saved cleaning 2/3 of the kiln shelves for this morning. Had figured the exercise would keep me warm in the cool morning. Just looked outside, and it is 28 degrees out there! I'm hoping it warms up at least 10 degrees while I eat breakfast.