fourth firing notes

The fourth firing was blessedly free of major mishap. we might have missed a thorough body reduction in some areas of the kiln, we had a trouble spot as we made the transition to oil, and one of the crew fell suddenly ill, but other than that, I think it is fair to say that the Tin Man and I are in good communication. lovely!

Loading:
back stack. again trying to make the front as dense as possible and the back gradually looser. for this firing, I was not convinced that we would all bring enough pots, so packed in some flowerpots on the layer the second up. I used these as saggars to experiment with some localized smoking of celadons- Richard had left me some salt-soaked driftwood, so some celadon bowls are loaded under the flowerpots with the wood. there is in this firing a crescent-shaped gap running along the place where the wall meets the roof, where the best I could do is have a little line of cups and bowls tumble-stacked onto a tall bottle loaded on its side. there are three of these bottles, all of them greenware. can you find the potter's mistake? hint- it's a tumble stack. see that small shelf off to the upper left? one half of that is on a post, one half is on some bottles... it's all nice an flat in the picture, right? I anticipated the shrinkage of the bottles as I put that shelf in, but two days later after the whole kiln was loaded, I reached my arm in a spyhole and lifted the far edge of that shelf and put a taller wad onto that bottle you see there so that the shelf was pre-tilted away from the direction of shrinkage and hence lessening the chance that the large bowl loaded upsidedown would slide off the shelf as its foundation shifted. good thig too, because during the firing, I was watching the shelf gradually flatten, gradually tilt towards the wall...

and i forgot to snap a shot of the front stack, it is just a regular stack of small pots and plates, but off to the far right are two very tall bottles. so the load was more dense to the left side by far, from both the front and back stacks. as I think back on the firing itself, I think this is responsible for the way the different burners operated. the left side of the kiln was more turbulent in general, which backed up all the way to the flame leaving the burner.

this photo is looking down at the firebox opening and the bottom shelf. more specifically, it is a photo of what I'm calling a bag wall- a short wall of bricks that block the most direct path of the flame from the firebox to the holes in the floor that lead to the chimney. this wall with the roll of wadding on top is solid in the front stack ( and open at the part of the shelf facing the door). it is perforated at the back stack- with half inch gaps between quarter posts. I post the shelves regularly- the shelf does not rest on this "bag wall"


Candle and slow rise:

started at 11 am saturday in one bourry box and the base of the chimney. at about five pm was a six hour candle and the kiln seemed to be dry. increased at 75 an hour after that. the intention was to burn large chunks of wood, getting the next one warmed on the grates as the previous was about half-done underneath the grate. as the temp increased, it became clear that it was also very helpful to have an occasional super-charge of cedar in there to help "catch" the log that may be a little too dense or have too little surface area to carry on it's own really well. I also opened some more primary air in the bottom which was very helpful too. (I should note that these boxes, despite my hopes, do not function as a bourry box really should- perhaps it is the low temperature at which we use them, but the kiln does not "pull" the air from the top of the box, through the wood and over the top of the coals- the primary air is at the floor, and the hole in the top of the box is a chimney that we keep closed) (unless we're just making pizza, not firing a kiln) . we stopped using the front boxes at about eleven hundred, at which point they were sort of maxed out anyway, pushed the coals into the center of the firebox and closed the damper behind them.

Transition to wood and waste oil:

was a little iffy for a moment. I think what happened is that I had the air open so much that I burned off the coals before the whole area was warm enough to ignite the fry oil. we tried stoking the big chunks of 3x3 oak like last time, but they just rolled down the bed of coals and got in the way. so then we switched to smaller pieces of fir and then little bits of cedar, but after an initial jump of temperature (burning off coals), we had a steady slow drop (Pop reading the pyrometer like a death toll). I finally consulted the previous log and discovered that the air had been at about 1/4 to 1/5, stoking chunks of oak, so we went with that and had steady success. so! next time: air 1/4, oil 1 and a half, maybe push some of the coals into the kiln early, to warm the area, and then rebuild them in the box, to be pushed in again. perhaps do that and also don't try to do everything at once- just push in the coals and stoke wood on top of them to build a pile of wood in various stages of burn with a mild amount of blown air before adding the fry oil.... I like that idea..

also worth nothing: as I designed this kiln, I had originally intended to push in the coals and then push in a triangular target brick to force the flame into a nice smooth curve into the kiln. well, such a target brick would quickly get glued to the firebox by ash, as does the damper that I slide into place after we're done with the front boxes. but in this case, it gets glued by ash dripping off the floor above it- major issue, poor design. perhaps I could bevel the edge of that floor so that the melting ash drips to behind it

I will take responsibility for nervousness that led to quickly establishing what turned out to be two hundred degrees an hour gain. of course this is dangerous, and we gradually scaled back. In an effort to make completely sure that we had indeed gotten over the trouble spot, I kept tweaking things to increase both air and oil. scaling back brought us near the original settings to oil 1 1/2, air at 1/3 open, stoking large chunks of oak every, ah, there are no notes on this- seven? minutes, then letting the kiln chew on it for a bit, then resuming.

Body Reduction:

I will also take responsibility for totally forgetting to check the cones- 1400 snuck up on me, and by 1475 we had cone012 down or soft in most places. 08 was down in the hottest spot. fortunately I had noticed a heavier reduction starting naturally prior to checking those cones, so I am somewhat consoled. of course we immediately made the changes to put the kiln into a reliable reduction and continued as such for the next four hours. four hours is because the kiln is actually rather large inside, and the difference between front and back take some time to even out. in the third firing, we were going with the idea that one hour or 08 to 04 is a sufficient body reduction, but the short of it is that we had some pale pots in the back, so that obviously didn't work completely well. so, Tim and Jack took the kiln through this stage and well into cone 7. it looks like they began alternating which side to stoke, continuing with the dense wood, and averaged an easy 100 degrees an hour. Tim's note at 5pm/ 1800/ cone 1 to 04 is that he closed the passives (I had opened 2/3 of them), and that the kiln seemed to be running rich.

Climb:

"running rich, not climbing" writes Tim, and closes all passives aside from the one that marks the opening to the active damper and the place where we let extra oxygen into the chimney to reduce its smoke. Tim turns up the air to 3/4, left the oil at 2. saw that the flame was reaching about four feet up the chimney (one small passive out), and started treating it like a wood kiln, which it sort of is. namely, watching the flame in that "blow-hole" disappear and stoking both sides now a few(?) minutes after the flame draws back into the kiln. he noted that the coal bed looks better with this treatment. two hours later he increased the air to full, coal bed still healthy. also closed half of the bottom of the chimney opening. soon after that, he increased the oil to 2.5, in the range of cone 1 to 4, and began alternating sides again.

Glaze reduction:

by about ten pm/ 2170/ soft cone 7 in the hot spots, it looks like he tried to amp up the oil to 3 but it didn't work, and opted for a little active and passive damper and a little less air (2/3). this seemed to be successful, and after I'd helped out my Pop get some medicine, we began stoking boards wrapped up with gail nichols mix of soda every other stoke. about half of the soda went in at this point (cone 9ish). I opted to stop for a time until we had cone ten down in many places since eleven is the target cone, and then there's the soak after that..

Soda:

at 2210, I opened the air a bit to get a little more rise and drop some tens ( 2 1/2, air 3/4), and soon after, plugged 3/4 of the passives, to try to move as much of the flame to the back, for even cones. cone 8 is down in the coldest spot (right back, nine is a third in its left equivalent). other than that, we have tens a third in the hottest parts of the kiln (upper forward). thirty degrees later I resume adding soda and put settings for a mild soak (oil 2, air 2/3, active damper 2 inches in). one hour later, I have finished with the soda, and am alternating oak chunks enough to keep what I hope is sufficient reduction, every threeish minutes.

Soak:

at 2;30, we are hovering at about 2250 with the air at 1/3, oil at 2, alternating the stoking, and there are really not coals. the oak burns completely, and the air wisks the ash onto the pots. the left burner has massive clinkers obstructing (?) it's flame path- if not obstructing, at least severely redirecting. I am taking my trusty flatbar and doing my best to smash them out of the way but it seems like it's a lot easier to smack them completely off the walls of the channel once they get huge rather than shave them down as they build, if I can get the right angle on them in such a restricted space. I am confounded by how effective the burner is with such a jungle gym to bounce through. the right side is nearly clear of them. why? is it the loading? is it the way I beveled the edge of the burner block? mystery.

Hot note:

at 4;30, 2270ish (two hour soak), I make settings for a hot note- oil 3, air full, passives in. tens are almost down in the coldest back, and 12s soft in the hottest places. at these settings, and alternating a frequent stoke, it takes about a half hour to bring the kiln to 2320 with cones 11 at about a third in the back, twelves at about a third in the front. LOVE IT

Reduce Cool.

ya, you're not done yet. Pop, who rebounded remarkably quickly, came to join me at the wee hours of the lovely night, marvel at the glowing Tin Man, and be my scribe for cone readings. but I dispatched him to bed again, since I knew I would collapse in a few hours and need his or someone's help for real. I chinked up the kiln at about 5 and began reduce cooling, stoking alternately into the floor and the fireboxes. Since I have liner glazes (mostly gail's red shino), I do not want to reduce too hard, and practice the Simon Levin method which he calls downfire: reduce, reoxidize, repeat. kind of a mellow reduce cool- I remember the "sparkleplenty" pots that he made for a firing or two in his little cat kiln by reduce cooling "proper", and many examples of scum and crust at Utah- no thanks- for this firing, I basically waited many minutes after any wisps of smoke had gone before stoking mildly again. certainly no belching smoke higher than 2000.

as i chinked up the kiln, it became clear to me just how much oxygen was coming in the fireboxes, so I abandoned stoking into that space, chinked the spy, and stayed with the floor only. we'll see how effective it is. I was hoping to find a great little indicator down low in the door but had to settle for reading a place where the chamber meets the chimney- also low. my hope is that since much of the wood was towards the front of the kiln, and the indicator, low and towards the back, that it shows an effectively distributed flame. trouble is that this way, I'm stoking right below openings in the floor that are closed, so I'm not sure quite how to -- maybe make a trick brick again, just for reduce cooling.- pushing aside a k-wool covering over the front holes..

Pop took over in the daylight part of morning, I fell asleep in the bathtub and then got a chicken from my buddies at Diggin Roots Farm roasting in one of the pizza ovens, Allison came over, we opened some champagne, made some smashing good pizzas, holy cats, I was in heaven. of course it could all look terrible in there, but just to have another successful firing lightens my step...

at the end of that day, monday, Pop remarked that it was probably a really bad idea to leave those burners in place, surrounded as they were by radiating heat but now without the cooling influence of air passing through them- (the electric motor has a varnish around each copper strand- should it melt, it would short the whole thing out) and sure enough, I removed them but had a tiny heart attack (again) when we plugged one in elsewhere and it ran really irregularly. so with my last ounce of energy, I cleaned the innards as he disassembled them to find out if I'd killed them. I hadn't. thank god. I clean them every time, but only one of the parts. anyway, thanks pop.

ah, so we went through about sixty-five gallons of oil, fifty sticks of oak 3inx3inx3feet, about nine cubic feet of cedar fence boards and a pile of fir and other assorted large chunks of wood that would be about three by three by four feet, ish. so, about another 2/3 cord of wood.

thinking to unload on sunday, if anyone cares to visit...

oh ya, and as I was checking email and news, I ran into this