dneese on fri 12 sep 03
Firing my Olsen 24 updraft for more than 12 years now I believe I know what
to expect from a cone 10 firing and load to match the areas in which certain
glazes work better than others. All we had in college were
Alpines even though the first hard brick kiln I built was a downdraft I
decided this time to put a kiln together and not have to stack up the door
too.
I normally set the alarm in the morning around 3 am. Turn on 8 burners on
the lowest setting with the damper and peeps fully open. Boost to 1 inch
pressure around 6 to 6:30 am. Ease gas pressure up slow through red heat and
reduction. Finish firing in the afternoon some times around 4 pm depending
on the weather. I am not in any hurry firing up or down.
In my Olsen the bottom fires out hotter than the top. I load all my
porcelains, celadon, plates and low items in the bottom third of the kiln.
These glazes look better with the extra heat. It is always cone 10 flat
probably cone 11 there. So I stack the most shelf mass, small kiln post
sized items in the bottom. Middle third is Shino and wood ash glazes. Some
blue glazes. Copper Reds in the very center of the stack. Usually 6 to 8
inch tall posts and pots there. I leave an inch or more space between the
pots and the next covering shelf. Top third is reserved for taller items
with 10 inch posts or higher. If I pack the top area near the flue the
bottom gets even hotter so I just leave plenty of head room in the arch area
not to restrict the path of the flame to the exit flue. I do not hang pots
out over the shelve edge in the flame path but still place pots with a
finger tip width apart sometimes closer in the stack. Use a mirror to check
distance it is so tight. There are a few places in the kiln in the earlier
firings where the glazes were not reduced seemed like. I was following Fred
Olsen's firing schedule for a while until I started turning on the middle
burners on low earlier in the firing than his recommended schedule. Seems to
have helped cure that problem with better heat and even reduction at 010-09.
Cone 010 drops over in the top first, easing in the damper at the top starts
reduction and moves the heat to the bottom area and the 010 cone there bends
shortly after the top. Hold damper and burner settings until cone 7 goes in
the bottom. Then it takes only a 1/4 inch adjustment in the damper to bring
a little more heat to the top still getting plenty of reduction. Close to
the end of the firing cone 10 in the bottom is halfway ahead of the top
cone. I ease out the damper a tich more an forget about the bottom cones and
watch until cone 10 is over in the top 10 to 20 minutes later. Soak for just
a very short time to clear up the atmosphere. Turn off the kiln and close it
up tight. Cover the top with extra insulation blanket over the flue area.
Drop my metal sides around the base to slow air filtration to the burner
ports. If I have some copper reds in the load and watch the color of the
cooling heat change I will stick in the peep a few strips of wood when the
pyrometer gets down around 1760 to 1750. Then forget it for 3 days. Unload
when you don't need gloves.
Dale Tex
"across the alley from the Alamo"
San Antonio, Texas USA
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