third firing notes

here's half of the crew of the third firing jst before lighting the fire in the left bourry box on tuesday july 7. Alyssa and Dianne. Tim joined us later after his day job. Jack was tending his dear lady and unable to join this time.

front stack.
back stack
wad gad
and once we were done with the bourry boxes, this was the first pizza. truly a delicious accomplishment's.

notes: analysis of results to follow in a few days. we will unload on thursday. peeking in, colors look great!

Stacking:
kiln was very uneven last firing, so trying to really force that flame to the back of the kiln with a tight stack in the front, loose pots in the back. the larger pots are much easier to load in the back anyway, so it was an easy plan to follow. I tried to load incrementally tighter as we moved to the door, allowing for staggering of shelves and groupings of pots so that there were some very tight spaces and also looser ones. there were six openings in the floor, three inches in diameter each, under the back stack. I rigged the trick brick in the chamber wall, and rested k-wool over two openings in the floor near the door, in case we needed more flue opening. There was a perforated bag wall of quarter posts that blocked the most direct route from the firebox to the damper. otherwise, no bagwall. stacking area is three feet wide by four feet deep by three and a half tall on average, with the firebox openings on either side of the four foot length. two days to stack

Candle and Slow Rise:
Candled for seven hours, in one box. one foot fire at the base of the chimney, to induce draw. increased temp 100* an hour after that, supposedly. But it's tricky, of course, because a small fire can easily be frightfully overstoked. so it looks like the night shift was safe and at an overly-slow rate of climb, bringing us to 742* by 6am on wednesday, when I took over. part of the problem is that stoking the boxes seemed to be very difficult because of the backpressure when the door is opened. I shut as much of the passive air openings as possible, a more thorough job than I had done before, and that did help somewhat. the shift changeover was bumpy. I thought I was doing exactly what the night shift had done, but the kiln suddenly jumped a hundred degrees in fifteen minutes. if there are cracked pots in there, it's probably from that moment. (same as second firing).

during this part, I was trying to get the primary air to draw from the top of the boxes, as a proper bourry box would do. I was not successful. basically, the kiln does not seem to draw hard enough at those low temperatures to pull air downward through the wood, through all the channel and into the chamber before it gets to the flue. perhaps it would help to chink every other possible air draw and passive damper. I suppose we could continue with the flame in the chimney to increase the draw, but that seems silly. Most likely, I will open a little more air space at floor level of the bourry boxes, and let the opening at the top of the box function only as a chimney for the pizza oven function. at about 800*, the coals began to clog up the opening, so I let the wood burn down, removed the front two grates, pushed the coals forward into the chamber, and resumed firing in the box. I did this on both sides but because the left box had been the starting box, it was significantly warmer than the right and so it "re-started" more easily than the right. Overall, there were a lot more coals on the left, which became an issue later. this did take care of some of the problem of backpressure at the door, but really, the boxes become maxed out at 1000*.

Transfer to Oil and Wood:
9 am at 1000*, I pushed the coals into the center of the firebox alley, closed the damper leading to the bourry-box, opened to the oil burner, and set the oil to fire at 1/5 of the available pressure. (* consider pressurizing the tank for better total pressure). this turned out to be too little, as Tim researched the old log entries to find that 2 had been the low setting in the past firing, with the air wide open. In this firing, I started out with 1/5 and 1/6th of the total vent open on the blower. remember to tilt the burner slightly forward or else the oil flows back into the burner and gets in the fan blades. I stoked short pieces of dense wood into the coal bed now at the center of the firebox to maintain a wick of flame into which the atomized oil droplets can fly. this firing, I did so with ozzie fishtail oak that had been used to separate shipping crates, so there may be some iron flakes on them. we'll see if it's a mess on the pots. I maintained a good bed of coals on the right while continuing to stoke the left bourry-box. temp hovered around 1070*. once I was comforted that the right burner was happy, I set about transferring the left side. this side was hotter to begin with, and had more coals. I pushed them too far into the channel and accidentally blocked off the opening through which the burner's fuel and air are moving. so when I went to turn on the blower, I had to leave the air on full for a long time to burn coals off, and then when the oil sprayed on them, it was more of a crust than a wick. eventually, I went in there with a flat piece of angle iron over the top of the burner port to break up the coals. it was half a day before the two sides seemed to burn hot and evenly.

questions- there was a lot of soot created between 400 and 1300* . too much? break an iron-bearing tile.
did the greenware in the kiln survive the rough treatment in this time as well?

Oil and Wood body Reduction:
by 11 am the kiln was settling into an increase of about 100*an hour. the pyrometer was on the right side of the kiln, and registered much more effective temp increase with stoking on that side of the kiln. (which was also the side on which the firebox seemed hotter in general). temp might spike as much as 100* in a stoke, nothing measurable from a stoke on the left firebox. Stoking two pieces of oak (3x3x9) and two pieces of cedar sticks every five minutes, watching the coal bed for a size that seemed healthy but not blocking air openings. at 1pm, Tim read up in the old kiln log and changed the air to full and the oil to 1 1/2, which led to a quicker cycle. the left coal bed began to catch up/ warm up. by 1:45 pm, temp at 1520, ^012 down top front. closer attention to maintaining reduction and passive dampers out to burn off excess smoke.. 3 pm 1675* , ^04 soft front right, ^012 down back left ( coolest place in kiln). by 4 pm ^1 is down the hot spot, pyro at 1800*, and a large pot has fallen into the left stoke aisle, occupying half the available space. but its position is such that it is acting as a bag wall to deflect the flame towards the cool spot. the doctor advises that perhaps there is not a problem yet, wait and see. every few hundred degrees, the oil turned up half a point

Evening :
Oil is 2.5, air open, passives in, active damper out, stoking

every so often (five to ten min). the general principle of the fuel situation seems to be that the kiln asks for a slowly shifting proportion of wood and oil, more wood at lower temperatures, just a bit later on.

the large pot in the stoke aisle didn't seem to be a problem at first. cones fell at the same rate on that side as the other. hot spots in the kiln were towards the front and middle, cooler at the very front by the door, and at the very back. throughout the evening there was a steady climb of about 80* an hour until cone 8 was moving in three places, at which time we commenced adding soda. oil down to 1.5, air at 2/3, passives out. six pounds total of the gail nichols recipe were painted onto small boards, and four pounds of baking soda was mixed into hot water into a sprayer in a dilute half and half solution. this makes seven pounds of soda going into the kiln. this is a 75 cubic foot kiln, about 50 of which is stacked, and no soda has been added before. the brick is high-alumina.

Night: at 11pm, kiln is hovering at 2060*, 31/2 lbs of soda have been added, and two gallons of water, in the process. the draw rings show a nice buildup, but of course they are right in the line of fire. the water cools the kiln about 100* as it is added. cones have been steadily dropping, but the right side of the kiln is notably hotter than the left and front, except for the pack stacked deep into the kiln, which is now equal to the right side. I am underslept, underfed, and rather nonchalant about directing the show. Richard and co show up with tea and good cheer, but it takes me quite a while to refocus on the fact that the kiln is not climbing as effectively as he could be, and I am not in adequate reduction. But I'm pretty dead, so at about one am, with Dianne's help, he takes over for a few hours as I catch some rest. They tweak little things and maintain about 2140*. the damper is a third closed, passives are out. oil at 3, air open about 3/4. there was little cone movement in this time.

Thursday Morn:
5 am. I close the passives and open the damper, turn up the oil and open the air, pull the trick brick in the back wall and push open the front two flue openings, all to no real effect. cone 8 soft at the door and far back of the kiln, tens at a half where they sit on the shelves closer to the center. I am able to get about a cone higher in the next few hours, but the oil at the left burner is leaking, unburned, where the large pot is pushing the flame backwards now. I break it with a piece of leftover flat bar snuck into a gap above the burner block, and manage to push the shards of it out the channel and into the bourry box. it did not seem to take out anything else in the process. yike!

for two hours, I notice no significant change. I'm still stoking small pieces, as my previous buddies had been, going with a less wood more often theory. but this kiln doesn't really run on wood at this point. I switch back to the large chunks of oak, building a coal bed, and the oil is now 4. I stoke one side and then the other, taking my cue from when the wisps of smoke leave the little cracks at the top of the kiln. this works well, and by 9 am, we are at 2222* with ^9 at 1/3 all around, 11 in some places. 9:30 is a whole cone hotter everywhere, almost two cones in the hottest spots. Chris Baskin highly recommends a three hour soak, at this temperature. we kind of soaked all night, at a cool cone 8. I would like to know how much more effective the soak is as the temp increases. Gail recommends a two hour soak after adding her soda mix ( which she does at cone 8)

Soak:
oil to 1 1/2, air 1/2. damper at half, passives out.
on a whim, I sprayed in the last two gallons of soda, which dropped the temp from 2250 to 2150. after the kiln regained only 20 degrees, I brought the oil and air up again, less than before (3) , and opened the damper some. kiln climbed in the next few hours to end on a hot note at 1 pm on thurs. I did a little experiment just before ending. Can the kiln increase temp on oil alone? I put the oil to 5, air wide open. the pyro rests at 2236 without change for five minutes, but as soon as I stoke one piece of wood, I get two degrees out of it. ^11s are down most places, 12 in one place. I'd say that's a hot note.

Reduce Cool:
shut all three dampers and pull the passives. done with the oil, and at first, tried to stoke just above the burner in that little spy-hole in the floor. wood got stuck on the clinkers. began stoking under the floor, where I had opened the opportunity of access to the sub-floor. I'm not sure how much smoke is too much until the glazes become solid. must research. a draw tile pulled at about 2100 revealed that we had not scummed the glaze. I did do a local re-oxidization for a mere 30* at 2200*, at the side-stoke holes, and the back spies. We began reduce cooling at 2030* , continuing to 1600*, which lasted 12 hours. Dianne did a fine job finishing off the firing. she stoked at the sub-floor and in the side-stoke. I popped some champagne, took a shower, and gave up on being intelligent.

the kiln cooled 1000* in the next 24 hours and then 200* in the day after that.