19 May 2009

firing the new kiln

Sometimes I still find it surprising how little I know about firing a gas kiln...it's not that I've had loads of experience but somehow, i guess i thought after 10 years of potting and firing gas kilns here and there with others, that the baseline knowledge would have been in my psyche somewhere...not so.

i have now fired my new kiln 3 times and from each i have gathered a tremendous amount of information. probably the most from my may 5 firing.

I had more pots than the previous loads so the stacking was a bit tighter but still only about 3/4 full. it seems that i have been under the gun each firing and am also so excited to get after it, that i have yet to fill her up. previous stacking had been too heavy at the bottom and very loose towards the top. i believe this has contributed to my uneven temps.

i had just been in n.d. for a week with potter girlfriends and fired a big kiln with power burners (i have 4 venturis) and we had a discussion about reading reduction out of the bottom peep...i had been relying primarily on the top for backpressure. this firing, i tried my best to get back pressure out of my bottom peep to no avail. i was reducing like crazy...i could smell it and was getting about 10 inches out of the top. what i did not realize is that reducing can stall out the temp which it sure did. it took me hours to gain 50 degrees but i just kept tweaking and waiting so the time passed quickly. only after i reviewed my log did i realize how freakishly long it took. i mean...at 4am, when i finally shut her down, i knew it was wayyyy too long and especially when i checked my propane tank and found i had used around 100 gallons of propane (ugh).

soooo.....i added another 2+ feet to my stack (picture above) and next time will chill on the reduction a bit. i did get beautiful shinos and my celadon was lovely. i need to figure out my temp/reduction unevenness though from top to bottom.

i reread a section in Vince Pitelka's studio book and noted the following tips for the next firing:

-no big adjustments to primary air (on burners) ( i was tweaking them a lot)
-when turning up the burners, open the damper slightly to allow things to equalize and then slowly close it
-cool bottom.... try damper out
-cool top.....try damper in
- at least 10 minutes of oxidation cleanup/clearing at the end. ( i had some bubbling and only cleared it for a few minutes) (again.....4 a.m.)

i'll fire again in a couple of weeks and update after....

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