Finished my test glazing. I have around 65 pieces with varying degrees of attachedness so I pick the little throw away pieces to test with. A mix of stoneware, porcelain, slipped stoneware, textured pieces, some organic material and small bowls.
I am testing Chinese White Crackle, Malloy Clear, No Craze Clear, Leach Zircopax White, Leach Temmoku, and refiring a few pieces with wood ash that did not melt.
I left the valve 1/4 open to let it warm up. At 11am I turn it up to full and after another hour it’s looking good and I added 2 bricks on the outside of the burner to further direct the heat.
Not wanting to cause eye problems down the road I don my shades so I can check the cones through the bright haze of yellow heat.
So I remove the side bricks to slow the process a bit. After cone 5 it stalls and I get a tip to slightly close the damper. No change after 15 minutes so I add the side bricks back. Cone 6 drops at 4PM but no change in temperature after that. I added a third brick on top to further direct the heat and cone 7 starts to drop.
By 6PM I see cone 9 starting to dip so I put it into reduction with a combination of closing the damper a bit more as well as the air flow on the back of the burner. The flame seeks oxygen so I know it’s reducing. I can no longer see the cones through the peep hole so I figure everything is good and since you lose a bit of heat during reduction my plan was just to let it go for another hour and cone 10 should be reached by that time.
I get curious by 7 and stop reducing by opening the flu a bit. I see cone 7 is still not flat and cone 9 is stuck where it was, softly bent. Confusing to say the least. I need more temperature. Not much I can do with the limited variables I have so I move the damper to the front of the kiln instead of the back, changing the airflow.
I cut the lid the proper width which is 2″ wider than the burner width or another inch wider than the burner port width according to the info on the Ward Burners site. This was to allow for this very situation so I’m glad I had the option.
By 8PM I figured it was the best I was going to do so I shut down the gas and closed the kiln the best I could to let it cool overnight. I got a very soft cone 10 out of it.
The next day I go back out to check the damage. Total failure save for the lessons learned. The problem with the entire firing, I hypothesize, is that the shelf was too big for the heat to efficiently rise. The bottoms of the pots had a better melt than the top. I probably got way above cone 10 below the shelf. The shelf was actually bowed.
The reduction was too early and too much which caused carbon coring. Even the porcelain was grey. This is due to not enough burnout of the carbon materials during the firing. This is undesirable as I have read that it weakens the vessel.
I don’t have pictures as they don’t even really bring any more insight. If you have a failure like I did, you will see for yourself what went wrong. I put them in my electric at cone 8 to see if the test glazes at least will melt given some even heat. I’ll post some pics after it cools.
So I spend the next day being ticked off, throwing some more pots and going over the firing again in my head. The next firing I will use 1/2 shelves which is my only other option for shelf sizes.
Another tip was brought up by a friend who suggested that a top shelf neared the damper on the inside will allow for more heat to stay in the kiln longer before exhaust.
I have enough LP and enough bisqued pots for another go. Maybe this Monday.
Don’t let anyone tell you that firing a kiln is not work. It’s exhausting to focus for 10 hours on something you have very little control over. It costs real life money to fire as well and after this firing all I can think about is how I was basically spraying quarters out of the propane tank for 10 hours straight.
Live and learn. Try not to have expectations on your first try. Then do it again, and again, and again, until you get it right. That’s about it.