Kristin on wed 18 dec 02
Hi all -
After learning that my tiny kiln works quite nicely, I
ventured into testing my big one. Okay, it's
medium-sized. It's a Cress; the size of your basic
Skutt 1027.
Followed the recommendations in RZ's "Electric Kiln
Ceramics," tried also to keep temperature rises to
within RR/JH's recommendations.
This failed miserably. A firing that should have taken
about 24 hours ended up taking less than 10. For
example, Richard recommends turning the kiln up to
"High" at 500 C, until you hit 1200 C many hours
later. RR/JH mention that slowing down the firing
close to 1200 C, which is necessary, is easy to do
because kilns generally have a hard time getting
there.
Um, she went from 500 C to 1200 C in Less Than Two
Hours.
So I've got some figuring to do, trying to get this
baby to slow down. A Lot. Anyone else have similar
learning pains? (From the very beginning, when I
turned all switches to Low, it went way too fast.)
The firing was pretty uneven. Cones at three different
levels showed that I way overfired on the middle and
bottom (looks like I got just past a ^7) but the top
shelf (only 3 inches or so from the roof) barely
started to bend the 6 cone. I have no computer
controller, just a pyrometer. I didn't use the cone
sitter.
I plan to just play with temperature settings until I
can figure out how to keep it slow and even -- turning
the top dial or two (there are 6, I believe) up higher
if need be. But is this incorrect? I don't have a vent
of any kind right now. It also cooled Very rapidly
(after I practiced soaking for a while, I just turned
it off). Could all of this be because it was empty
besides the cones?
Thanks to everyone for your continued advice. Can't
wait until I can share pictures of this adventure
(although I do use extruded handles so I’m nervous
about ever sharing photos now!).
- Kristin
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Sandy Cryer on thu 19 dec 02
In a message dated 12/18/2002 10:50:32 AM US Mountain Standard Time,
kschnelten@YAHOO.COM writes:
> ). Could all of this be because it was empty
> besides the cones?
>
>
an empty kiln will fire much faster than one filled with ware. The pottery
and shelves take a lot of time to absorb the heat, lengthening the firing
time. I have found with my old cress kiln: Low for 2-3 hr., med for 3-6
(depending on the thickness of the ware), then turn to high. This has taken
9 to 14 hrs depending on the age of my elements. A much long firing can be
achieved by using one dial at a time. For example: 1 dial on low for 1 hr, 2
dials low 1hr, 3 dials low 1 hr, 1 dial med 1 hr etc until all are on med.
then leave for 3 hrs, then all then 1 dial on high for 1 hr, etc. This method
can be varied to adjust firing speed. Also stagger the shelves and don't
stack any higher than 6" from top and only on one side. I use the kiln
sitter with a ^6 bar, when the flap falls and turns the kiln off, I lift the
flap back up, push in the button, then lower the flap very carefully so the
button doesn't pop out. Turn the dials to med. and set your oven timer (I
must do this, or I forget) for the soak time (I soak for 30-60). I get ^6
bent 1/2 to 3/4 (not quite touching) from bottom of the kiln to that top
shelf and ^6 just starting to bend on the top shelf. This works great for my
glazes. If you want ^6 touching I would put a ^7 mini cone in the sitter.
Hope this helps.
Sandy Cryer, leaving cold arizona for colder colorado today, but get to see
my grandbaby!!
Brad Sondahl on thu 19 dec 02
The real question is why you would want to fire so slowly? I don't know
the reference you're using, but there's no reason for an electric kiln
to take 24 hours for a firing--you're wasting a lot of energy to do so.
It's my experience that 6-8 hours for bisque (besides preheating time
for removing excess moisture) and 7-10 hours for glaze (even to cone 10)
are quite suitable. The only danger in going fast with a glaze firing is
the temperature of alpha-betz quartz inversion, which can cause some
cracking if rushed through. One of the beauties of an electric kiln is
that with good elements they can be fired on a 24 hour total schedule,
from start to unload, so that daily firings are possible.
Brad Sondahl
--
For original art, music, pottery, and literature, visit my homepage
http://sondahl.com
Pottery sales page http://sondahl.freeyellow.com
My music site at mp3.com http://www.mp3.com/sondahl
Ron Roy on fri 20 dec 02
Hi Kristin,
That is too fast - I am thinking something might be wrong - is the wiring
and voltage right? Maybe the kiln was empty except for the shelves?
Anyway - if you know how to soak it then you will know how to slow it down
- You need to use cones to find out how accurate your pyrometer is. If you
set the switches a little higher than the soak setting it will be a good
place to start.
If the middle is hot you may just find a slower rise will make a big
difference - heat radiation needs time - fast firing is a good way to get
uneven results.
RR
>The firing was pretty uneven. Cones at three different
>levels showed that I way overfired on the middle and
>bottom (looks like I got just past a ^7) but the top
>shelf (only 3 inches or so from the roof) barely
>started to bend the 6 cone. I have no computer
>controller, just a pyrometer. I didn't use the cone
>sitter.
>
>I plan to just play with temperature settings until I
>can figure out how to keep it slow and even -- turning
>the top dial or two (there are 6, I believe) up higher
>if need be. But is this incorrect? I don't have a vent
>of any kind right now. It also cooled Very rapidly
>(after I practiced soaking for a while, I just turned
>it off). Could all of this be because it was empty
>besides the cones?
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Ron Roy on fri 20 dec 02
I think 10 hours for a cone 6 firing is too fast for a number of reasons.
Giving the time for temperatures to even out in a kiln is a good way to cut
down on glaze defects like pin holing - we need to keep in mind - any
reduction of seconds more than pay for the extra firing costs - so firing
slower can actually result in savings.
I can't say what the optimum speed of firing is in terms of saving
electricity - it would be an interesting experiment - but there is an
efficiency ratio there.
I also think 25 hours is too slow - there is a point when longer firings
are not worth the cost - and can result in increased cristobalite
production under some circumstances.
My general rule is never go faster than 100C per hour - and that should be
slowed to 50C 100C before the end to give glazes and clay a good chance to
melt and combine properly as well as even out the temperature throughout
the kiln. That is at least 14 hours on the way up.
There can be a speed up at the beginning if the glazes are dry when stacked
so it is acceptable to go faster from beginning up to 600 - so maybe that
time could be reduced to 10 hours but I would not recommend lower than
that.
Firing slow during the quartz inversion is not necessary by the way - think
of how much raku goes through the inversion on the way up with no cracking.
The physics are quite different on the way up - rim gets bigger faster than
bottom - compression - not a cracking situation.
Cooling is different - rim gets smaller before the bottom - tension results
in bisque dunting.
RR
>The real question is why you would want to fire so slowly? I don't know
>the reference you're using, but there's no reason for an electric kiln
>to take 24 hours for a firing--you're wasting a lot of energy to do so.
>It's my experience that 6-8 hours for bisque (besides preheating time
>for removing excess moisture) and 7-10 hours for glaze (even to cone 10)
>are quite suitable. The only danger in going fast with a glaze firing is
>the temperature of alpha-betz quartz inversion, which can cause some
>cracking if rushed through. One of the beauties of an electric kiln is
>that with good elements they can be fired on a 24 hour total schedule,
>from start to unload, so that daily firings are possible.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Lois Ruben Aronow on sat 21 dec 02
Could there be an detrimental effect to the ware if the firing takes
less than 10 hours?
My firings always seem to be less than 10 hours. Used to be 8, but
now, with my tiring elements and higher top temp (2205 F) I am getting
to about 9 1/2 hours.
Most of my ware looks fully fired with few apparent glaze flaws, with
the exception of my purple beading glaze, with which I have terrible
terrible terrible terrible spitting problems (only happens with the
purple). =20
Do you have any suggestions as to the what an ideal rate of climb
should be? Is it really 100F per hour??
--------------------------------------------
Lois Ruben Aronow
gilois@bellatlantic.net
=46ine Craft Porcelain
http://www.loisaronow.com=20
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