Donna Kat on sun 1 may 05
We have been having problems with our kilns but our last firing is the most
bizarre we have had to date. We fired 2 kilns starting at the same time
with the same ramping schedule. It is a modified version of MC6's posted
version
Segment Rate Temp Hold
1 100 220 0
2 350 2000 0
3 150 2180 25
4 500 1900 0
5 125 1400 0
Both kilns had comparable pots and the same glazes. Both showed the same
cone characteristics (top shelf cone 5 flat cone six tipping and the other
shelves show cone six past middle but not quite flat). #1 kiln took 18+
hours to fire and #5 kiln took about 14+ hours. The firing unless my math is
way off should have been about 13hours.
The glazes in kiln #1 were perfect though still overfired (a little pitting
on one piece). The glazes in kiln #5 were a disaster. A large percentage
of them had severe crawling. The glazes this showed up on are floating
blue, MC6 Spearmint, MC6 Bone, Raspberry - I think that is it. The other
issue that we saw was a pot cracking as if their was a glaze fit problem but
I think this is a different issue because I have been finding people
sneaking in non-studio underglazes and clays.
So... what are the thoughts on this?
Cindy in SD on sun 1 may 05
Dear Donna,
I'm not an expert on the glazes you mention, but I can't see anything
wrong with your firing schedule. Also, I wouldn't be concerned about my
kiln taking longer to fire than the program I set for it. Depending on
the condition of your elements, the distance from your electrical
service, the density of the pottery being fired, and probably other
factors I'm not thinking about, a kiln can take quite a bit longer or
shorter a time to fire than its neighbor.
I suspect that maybe the person or persons who applied the glazes in #5
kiln may have done so over dusty bisque ware. I have gotten crawling on
one occasion when refiring pots that had been the victims of an aborted
glaze firing, but if your glaze firing had been interrupted long enough
to cause this fault, the kiln would have aborted the firing and
displayed an err 1 or an err p message.
Good luck tracking down your troubles,
Cindy in SD
Jim Willett on mon 2 may 05
On Sun, 1 May 2005 11:28:57 -0400, Donna Kat wrote:
>We have been having problems with our kilns but our last firing is the
most
>bizarre we have had to date. We fired 2 kilns starting at the same time
>with the same ramping schedule. It is a modified version of MC6's posted
>version
>
>Segment Rate Temp Hold
>
>1 100 220 0
>2 350 2000 0
>3 150 2180 25
>4 500 1900 0
>5 125 1400 0
>
>Both kilns had comparable pots and the same glazes. Both showed the same
>cone characteristics (top shelf cone 5 flat cone six tipping and the
other
>shelves show cone six past middle but not quite flat). #1 kiln took 18+
>hours to fire and #5 kiln took about 14+ hours. The firing unless my math
is
>way off should have been about 13hours.
>
>The glazes in kiln #1 were perfect though still overfired (a little
pitting
>on one piece). The glazes in kiln #5 were a disaster. A large percentage
>of them had severe crawling. The glazes this showed up on are floating
>blue, MC6 Spearmint, MC6 Bone, Raspberry - I think that is it. The other
>issue that we saw was a pot cracking as if their was a glaze fit problem
but
>I think this is a different issue because I have been finding people
>sneaking in non-studio underglazes and clays.
>
>So... what are the thoughts on this?
>
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Donna,
We used to have unexplained crawing of some of our glazes and found
that to some extent it seemed to be related to how dry they were on the
ware and how fast we took them over the boiling point of water. We started
soaking them under 200 for a few hours and then ramping and have seen the
crawling problem disappear. We also ease our ware through the transition
stage of 900 to 1200 at 200 but that may be more a personal preference
thing than a requirement. After all these are just guidelines...not
rules. As to the different firing times on your kilns it could be
mechanical. We have found just when we think we know exactly how our kilns
will fire they manage to surprise us. We do know that firing times vary
depending on what time of day we fire. Seems to possibly be related to how
many other people in your part of the world are using electricity at the
same time. Daytime firings take longer than nightime firings here.
Hope this helps.
Jim and Cindy
Out of the Fire Studio
Edmonton, Alberta, Canada
http://www.outofthefirestudio.com
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