Kiln firing; fire gud

[Adios Pantalones]

So I promised I'd take a mess of pictures of this latest firing. We loaded the kiln until 2 am on Thursday, then another 6 hours on Friday and started firing at maybe 4 on Friday. (pics from the first firing)

First we set a small fire in the chimney to get the draw going, and brick up the access door to the chimney, then start smll fire outside the firebox. (pic from first firing)

The chimney pulls the heat into the firebox, then through the ware chamber whee the pottery is stacked on refractory shelves.

The temp is increased to 200 F and held there for a few hours. The fire is moved into the firebox and the temp is slowly raised to 400 F over the next 2 hours. A coal bed is built up in the firebox until it's several inches deep. The fire is then moved to the "hobs"- bricks that form small shelves on either side of the firebox that will support wood 40" long.

The air hole at the bottom of the firebox is bricked up- air is drawn therough the wood on the hobs and essentially burns upside down- as the flame approaches the coal bed it's super heated before going through the throat into the ware chamber. Here's Rachel (art student hippie) next to the firebox.

Here's the firebox rockin' away. Some bricks used for air inlet have been removed so you can see the yummy fire. Rachel and Mike (pottery hippies) are tending the fire.

In fact here are a list of the air controls-
The door- primary air is drawn through a space under the door.
Secondaries- 2 holes in the front are used to introduce supplementary air just under the wood on the hobs.
Front door (wombat hole)- start the fire there, and close it up a bit at a time to reduce the cold air coming in.
Damper- a shelf is used to close off the chimney flow.
Passive dampers- 2 bricks on each side of the chimney (in the collection box) are pulled out to create a space the chimney draws through to slow air on one side of the kiln.
Mouse holes- 3 holes under the firebox lead to openings in the floor of the firebox to add air under the coal bed.
Sidestoke ports- wood is added directly to the ware chamber through these 2 ports to add heat, reduction gases, and ash to the top of the kiln.

The kiln gets to over 2300F- hot enough to melt the ash produced, which forms a "glass"- a glaze on pots. With the Bourry box firebox (upside down burning)- as ash is produced and it falls- it gets entrained into the airstream/fire and carried into the ware chamber. At about 1500-1700 F we reduce the air and load up the fuel to get incomplete combustion on purpose- a "reducing" atmosphere- like gasification without enough oxygen to finish combustion. At 2300 we soak the temp for a couple of hours to melt any remaining crusty ash on the pots and shut it down carefully.

 

[Adios Pantalones]

More pics- Rachel and Mike

Chimney blowin flame at about 2000F in the ware chamber

Dave (another hippie) on his hammock at 4 am near the chimney. He woke up saying "man it's sticky out here"- probably 120F back there, and I pulled a passive damper brick right under him

Here's dave taking down the hammock before it catches fire

Here's me with my splittin' machete

A little less than half the wood- we burned mybe 1.5 cord in about 18 hours- our fastest firing yet!

You can sort of see the "cones" in this blurry picture- they each bend at a certain heat work- not really a temp- you need to soak at a temp to get certain things to melt. It's sort of like when you cook a turkey you don't just get the oven to 325 and it's done- you need 20 mins per pound. We shot for "cone 11", but got over cone 12 on the bottom of the kiln which is always hotter in my kiln.

We'll open tomorrow and I'll have more pics for you

 

[Apprentice_GM]

That is just awesome AP! Great descriptions. What a fascinating hobby, particularly the FIRE bit

An 18 hour burn seems a lot more efficient than a 10 day burn (eg that Japanese anagama site) - is that the difference between Bourry Boxes and anagamas or just different pottery outcomes desired?

What is with the 11 or 12 cones? More cones is hotter, from your post, but why do they appear at all?

Anyway, very impressive!

 

[savageactor7]

WOW pretty incredible ...looking forward to see todays pics.

 

[Adios Pantalones]

App- the "cones" are a scale. You buy cones that melt at different temps/heat work to estimate if the clay has vitrified and the glazes are melted- so "cone 12" has a different composition than "cone 10" (so a cone pack for me has a cone010, 6, 10, 11, and 12). Cone 010 (then first "0" means it's on the low side- sort of like a negative sign) tells me that the carbon is burnt out of the clay and I can start reducing to get other effects. I like having 6 in there to tell me I'm making progress. I'm shooting for cone 11, so 10 tells me to even out the kiln and try and get cone 10 to fall on top and bottom of the kiln on both sides.

Those long firings in Japanese kilns are for a few reasons- anagama literally means "cave kiln". The first kilns were dug out tubes into an embankment- and the modern anagama are long tubes as well that mimics the originals (probably first in Korea, I believe)- sometimes rising from firebox to the chimney end. They are often very large- hundreds of cubic feet. Heating up that mass, in that long configuration takes a lot of time. The firebox is "crossdraft"- air comes in one side and carries heat up the tube- the Bourry box is much more efficient. Efficient is not what people want in this sort of firing, and in fact I built in a couple of slight inefficiencies to increase the "woodfired effect" on my pots. The effects are different and more intense in an anagama, and highly prized by folks that are into it- sometimes with heavy gobs of melted ash on pots. That aesthetic is not for everyone, and I admit that some of it eludes me as well.

 

[Jags]

Very cool. I would bet that some frosty adult beverages would be in order during that process.

 

[fossil]

Well, that's just pretty dang cool, AP...thanks for the slide show. Rick

 

[smokinj]

same here thats awsome

 

[Adios Pantalones]

Thanks guys. That chimney is 15' tall, so the fire travels about 21' before blowing out the top another 2-3'. When you look into a side port and see these amazing swirling flames- it's like looking into hell. I hear those Tuvan throat singers chanting every time...

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Jags- a bit of that happens, ya! You have to be alert and awake though. You stoke at very specific times when the kiln tells you to- can't miss it or you lose temperature

 

[Tfin]

Very interesting AP. How long have you been at this and do you sell any of your pieces?

 

[Corey]

Neat kiln!! also...reminds me that I never get tired of seeing chicks in leather welding gloves! I am surprised to see so much actual fire going up the chimney, though. Maybe it's needed to draw in fresh air to bring up the temp - but wow! 1.5 cords is about 1/2 my heating needs for the entire year!

Throw up some pics of the aftermath if you have them.

 

[Adios Pantalones]

tfin- I don't, but I may start soon selling stuff. House fills up quick, and the hobby should be self supporting.

Cozy- you actually limit the fresh air coming in because it cools off the kiln and screws up some glazes too. If you think about a normal open fire being something like 800-900 F (am I close there?), and a woodstove being in the 500 F range- then you see that getting that big ware chamber in the first 2 pics- with the hard brick interior sucking heat, as well as the bricks, shelves, and pots loaded in there- to 2350F- you need the wood to blast out all its heat as quick as possible.

Some of the fire is created at the chimney- remember I said there was incomplete combustion on purpose? Well, the still combustible gases gather after the ware chamber and go up the chimney. Some air may be mixed in here from the passive dampers as well- so you have hot combustible gases mixed with air moving through a tube and bingo- you made yourself a giant blowtorch

 

[Tfin]

tfin- I don't, but I may start soon selling stuff. House fills up quick, and the hobby should be self supporting.

Sweet! Keep me updated if you do.

 

[ScottF]

That is very cool stuff, Thanks for sharing it with us and showing pictures. I love to see handcrafted items and lean how they were made. Thanks again. Very neat.

 

[ScottF]

I have heard of a phenomena called flash over, when everthing reaches its spontaneous combustion point and the flames just dance on the ceiling like angels. They say it is very mesmerizing. Is that what is happening in the kiln?

 

[Adios Pantalones]

I think flashover happens in houses etc- when the material that the room is made of hits a flash point- the ceiling/walls etc gasify. In the kiln- wood gas and flame etc are drawn through the kiln so it's different. However- the flame enters through the throat and much of the heat/flame rises. It has to pass by tightly stacked shelves of pots before making its way to the exit flue in the bottom of the back wall, so the currents and turbulence make the fire do some neat stuff. When in reduction- if you open a side port- air coming in allows the gases to combust and there's crazy fire streaking into the kiln. If there's backpressure- sooty flame comes out at you- sometimes with a "pop".

 

[tkirk22]

Cool Pics AP. Thanks for sharing.

So are you hiding a Bob Ross 'fro underneath that headware?

I just looked on youtube for any old clips of him. There were none to be found but the following clip made me lmao last night. My wife said 'I don't remember him looking like that'. I made a huge mistake and told her it was a parody.

http://www.youtube.com/watch?v=Cyli59EbOM4

I hope to paint like him one day. I think I'll be in a nursing home by that time though so my medium will be toothpaste and food.

BTW, For you younger folks, Bob Ross is the guy in AP's avatar.

Edit: Pasted wrong clip

 

[Adios Pantalones]

Opened the kiln

There's stuff from 6-7 of us in these shots

One of mine- the white texture is from attack by sodium in baking soda- too cool. We love this effect!

More of mine

Everything on the right board is mine- not sure whose butt that is though

The Octopot. Have to give it to an HP Lovecraft fan.

My new garlic keeper- need a big one kuzz I grow it.

 

[Jags]

Totally mega-cool. WOW. Some really - really nice work in there. Is it my imagination or does it look like some of the projects "melted"?

 

[Apprentice_GM]

AP, that is just terrific! Thanks for the pics and info, amazing.

What's the controlled cool down process? How long does it take? How do you do it?

How useful are novice helpers during the burn phase - like can anyone follow instructions whilst you sleep, or do you need to be awake and controlling the whole thing, or at least at the important stages?

That octopot is very cool. Congrats on some great pottery there!

 

[Tfin]

Very cool indeed! I love the pitchers and pots/containers! The "earthy/natural" look of these pieces is what does it for me. I could see items like these getting significant use at our place.

Well done! One other question........how often do you have these sessions? Couple times a year etc?

 

[Adios Pantalones]

Thanks guys!

There weren't any that melted per se, but a couple of platters that were on the bottom near the firebox were wet and exploded- ruining several pots. Another couple couldn't handle the extreme conditions and cracked- one actually ripped open in the strangest way (very thinly made pot).

The interior of the kiln is hard brick, so when we are done firing it retains heat and allows the kiln to cool slowly. At the end of the firing we sometimes add wood to the firebox and shut all ports. Smoke escapes where it can, and flames erupt, so I open the damper a bit to minimize fire hazard.

Novice helpers are great for most of the firing. Even those with some experience can be trouble if not careful- on this firing I awoke to find that they were psyched about the temp gain they had made, but had not put it into reduction when they should have. Oops. Oh well- this really was a very good firing, and the hippies were happy.

 

[Jags]

Nothing like the sight of happy hippies bouncing around. :lol:

 

[Adios Pantalones]

Nudity... Spontaneous drum circles...

During the firing a friend remarked that we had our own Burning Man festival

 

[potter]

Nice firing, AP. Shoji would approve. ;-)

Have you had a chance to do any workshops, Penland , Arrowmont etc.?