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.
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.
