Nana on tue 4 may 04
Yesterday, during firing (electric, no computers), the power went out
for about three hours (the kiln had already been firing for 17 hours
at this point). After the outage, we (maybe foolishly) just let it
turn back on. It ran for another 7 hours, then the sitter cone did
its thing.
Everything is horribly underfired. Which is better than overfired.
But is that a reasonable reaction? It doesn't make sense to me. I
thought the heat soaking would have made the kiln overfire. What
gives?
Could it be the sitter cone doing strange things?
And for future reference, should we have just let it cool completely
and started over again next day?
I am baffled!
Nana Underhill
BobWicks@AOL.COM on tue 4 may 04
In a message dated 5/4/2004 10:10:54 PM Eastern Standard Time,
erthbubble@COMCAST.NET writes:
Nana
I think I may be able to give you some insight regarding the under firing of
your kiln. Just stop and think how a pyrometric cone functions. Not only is
it the temperature but also the soaking or time element. When you allowed the
kiln to go on, it was like starting the kiln fire from the beginning, however
the cone had already begun to bend, so it turned the kiln off before the
glaze had a chance to flow. I would wager that your next fire will be normal
(that is if you have no power loss).
Good Luck.
Bob Wicks, Prof Emeritus, Art & Photography
Harrisburg Area Community College
william schran on thu 6 may 04
Nana wrote:>Everything is horribly underfired. Which is better than overfired.
But is that a reasonable reaction? It doesn't make sense to me. I
thought the heat soaking would have made the kiln overfire. What
gives? Could it be the sitter cone doing strange things?<
Sometimes a longer firing at slightly lower than optimum cone
temperature may result in what appears to be a proper glaze melt. But
you can't rely on the kiln sitter to provide accurate information.
You should always fire with a set of witness cones for accurate
measure of heat work.
I'd check each piece for any crawling, etc. then refire, slowly at
first. But before that, check your elements if the firings are
getting progressively longer. May be time for a new set of elements.
Bill
Nana on mon 10 may 04
william schran writes:
> Nana wrote:>Everything is horribly underfired. Which is better than
> overfired.
>
> But is that a reasonable reaction? It doesn't make sense to me. I
> thought the heat soaking would have made the kiln overfire. What
> gives? Could it be the sitter cone doing strange things?<
>
> Sometimes a longer firing at slightly lower than optimum cone
> temperature may result in what appears to be a proper glaze melt. But
> you can't rely on the kiln sitter to provide accurate information.
> You should always fire with a set of witness cones for accurate
> measure of heat work.
>
> I'd check each piece for any crawling, etc. then refire, slowly at
> first. But before that, check your elements if the firings are
> getting progressively longer. May be time for a new set of elements.
>
> Bill
>
You're right, I should be using witness cones. Honest truth, I'm not
even qualified to be firing the kilns, but we don't have anyone
qualified to do it. (Studio of about 80 users, low budget.)
We are definitely in need of new elements - firings are getting longer
and longer, soon they will take longer than the timer has on it.
I've refired the pieces, in another kiln, and believe it or not they
are still underfired, but this is just a matter of calibration and a
mysterious cold spot.
Man, am I glad I don't run a studio for so many people. Seems like
kilns get used up faster than napkins.
Thank you for your response, it's been helpful.
Nana Underhill
william schran on tue 11 may 04
Nana wrote:>Man, am I glad I don't run a studio for so many people. Seems like
kilns get used up faster than napkins.<
Kilns, like any other machinery, have a "life" span of usefulness.
Abuse and carelessness result in a shortened life, a bit of care and
fixing the little things often result in a longer life. Depending on
number of firings, how high the firings, the length of firings and
how clean they are kept, the elements have various life spans. For
our kilns at school - 18 - 24 months is what we get out of a set of
elements before I change them out. As time goes on, the firings just
take longer & longer, until the point where the kilns are turned on
6am and don't finish until after 9pm, I'm ready to go home....ok,
change the elements.
Bill
Nana on thu 13 may 04
Thanks for the response. I thinks that's it, the elements are just
old, but the repairman says they're fine.
The kiln has no vent, we fire it twice a week to cone 8, and a firing
takes 21+ hours.
Anyway, the studio will be getting a Technical Director soon, so we'll
have someone who knows what they're doing. :)
Nana
william schran writes:
> Nana wrote:>Man, am I glad I don't run a studio for so many people.
> Seems like
>
> kilns get used up faster than napkins.<
>
> Kilns, like any other machinery, have a "life" span of usefulness.
> Abuse and carelessness result in a shortened life, a bit of care and
> fixing the little things often result in a longer life. Depending on
> number of firings, how high the firings, the length of firings and
> how clean they are kept, the elements have various life spans. For
> our kilns at school - 18 - 24 months is what we get out of a set of
> elements before I change them out. As time goes on, the firings just
> take longer & longer, until the point where the kilns are turned on
> 6am and don't finish until after 9pm, I'm ready to go home....ok,
> change the elements.
> Bill
>
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