Hendrix, Taylor J. on tue 20 may 03
Howdy all:
Find below the details of my latest raku firings. It was an event.
This last weekend the wife's entire family came for a visit (15 humans
and 3 dogs in a 1400 square foot house--ouch) and on Saturday they had
the opportunity to glaze some raku pots and watch them fire. As Tony
would say, there were a few racers. And all were happy.
Although I have had several clayarters help me with my over long firing,
I decided to keep the firing pressure at 12psi for now. I dialed the
regulator to 12 and just used the needle valve for stepping up the
burner. I also left the burner port at its original configuration. I
did, however, cover half the 6" flu hole after the first 30 minutes of
firing or so, and that seems to be a big aid in cutting down the time
for second and subsequent firings. Because I was having too much fun
popping jiffy pop popcorn over the flu hole, our last firing of the
night was a long two hours and when we pulled the pots things were
almost white hot. May have shut down the flu too soon on the 4th firing
and that is the reason for the longer time. However, the end point was
probably the hottest we have seen in this kiln, so I am not sure what
was going on there.
I am confident that I can get the firing times below 1 hour for the 2
and third firings. =20
Can't wait to do it again.
I do hope to get some pictures of some pots. They left with the family,
but some of them have digital cameras.
1st firing 5-17-03
5:41 12 psi/ needle open to a fast yellow flame/ flu full
5:52 12 psi/ burner up a good 1/2 turn
6:14 12 psi/ burner up 1/4 turn
6:35 12 psi/ closed flu halfway
6:48 12 psi/ burner up 1/2 turn
7:00 12 psi/ old elements showing red
7:19 12 psi/ white crackle showing 'wet'
7:35 Pulled
2nd firing 5-17-03
7:40 Loaded second batch while burner candled. Barb didn't like that.
12 psi/ Needle opened to a strong yellow flame/ flu full
7:50 burner up 1/4 turn
8:03 burner up 1/2 turn/ closed flu halfway
8:12 old elements showing red
8:27 starting to melt. Red hot pots!
8:30 glossy
8:45 Pulled
3rd firing 5-17-03
8:55 New load/ burner at fast yellow flame/ flu full
9:10 burner up 1/2
9:27 burner up 3/4/ flu closed halfway
9:37 old elements red hot
9:55 looks white hot to me
10:00 burners turned down and Pulled pots
4th firing 5-17-03
10:07 burner at fast yellow flame/ flu full
10:18 burner up 1/4 turn/ flu half
10:25 jiffy pop failure--foil rupture!
10:30 2nd jiffy load
10:33 jiffy off/ burner up 1/4 turn
10:51 burner up 1/4
11:32 burner up 1/4
11:47 burner up ~1/4 but doesn't seem to be getting hotter
12:04 glaze bumpy?
12:10 Pulled--HOT/ felt kiln lid's wire handles through gloves. Kiln
interior white hot
william schran on wed 21 may 03
Taylor wrote about longish raku firings and what has been tried to
shorten the time. Has covered 1/2 of a 6"flue opening.
Measure your burner port opening, then make the flue opening 1 1/2 to
2 times that size.
12psi seems very excessive if you're using propane. We start our
first firings at 2 psi and never get above 3 1/2 - 4 psi. Our first
firing takes about an hour in a 4 cu. ft. kiln. Successive firings
get shorter until we're pulling every 1/2 hour.
Don't know how your burner is positioned, but if it's natural draft,
I'd keep at least a 1" space between it and the burner port.
Bill
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