The Slack-DeBrock Family on mon 21 jul 97
Greetings everyone. Lately i have been noticing more incidences of bloating
once a piece is fired- small bumps in the clay body only noticeable after
the glaze firing. This happens both in my wood-fired kiln as well as the
electric, and at a workshop with Jack Troy, he noted that soaking a bisque
firing when at temperature will burn out anything that needs to be and
solve the problem. Trouble is, I didn't ask enough questions, and am
wondering what others do for soaking. I have an L&L kiln with 4 rings and 4
switches, and I've just been guessing at the soak length and how many
switches to leave on for how long. So, if anyone can give me advice on the
fine points of a bisque soak I'd appreciate it. Do you leave all switches
on but set at low? Or just a couple of rings going? I do not use a kiln
sitter, just cone packs in there, and want to avoid spending money on more
equipment to measure temperature. I guess the big question is how long it
takes to burn out the bloating bugs and to do it but not overdo it. I'd
also be interested in hearing what people do when soaking a glaze firing-
again- how many switches, set where, and for how long, and what the
advantages are . i have heard glazes are "richer" and more beautiful whan
they are soaked, but wonder technically why and if people have found that
to be true. (Not talking about crystalline process) So thanks in advance
for any help out there!
Joan Slack-DeBrock/River Run Pottery
P.O.Box 95
McNaughton, WI 54543
715-277-2773
riverrun@newnorth.net
Karen Gringhuis on tue 22 jul 97
Joan - based on the advice of the Orton Fdtn & 2 faculty at Alfred
univ., from the time my bisque reaches 1000 F (roughly red heat), I
allow the temp to climb NO MORE THAN 100 per hour. When big C/06
goes over (this is my goal temp.), I shut off the kiln.
I would not fire without a digital pyrometer period. It has been
the best $250 approx. I have ever spent. I know right where I'm at,
I know in advance when my kiln elements are dying, I LOVE IT.
As for glaze, I hold the temp (or allow only 10 - 50 degrees
of drop) at top temp for at least 2 hours. Again, the pyrom.
tells me whether the kiln is climbing or holding -
it's essential. Then I SLOW COOL - in my elec. this means
I drop from 2300 to 2200 as fast as I want, then drop the
next 200 degrees at no faster than 1 degree per minute.
I watch the pyrometer & a digital clock w/ seconds on it.
I tallye the temp every 5 minutes & can control the drop
very well. (My dials are 1-12 settings.)
All of this results in no bloating from outgassing from
stuff not burned out in the bisque and also very very few pinholes
from glaze not healing over after firing. My results are
right on & selling (!glory be!) very well.
I understand not wanting to spend $$ but I think a DIGITAL
pyrometer is essential. I see no need to eternally fly by
the seat of our pants when we have new tools avail to us
which previous generations did not. I allow intuition &
serendipty into the rest of my process but IMHO they
have no place in elec. firing.
Hope this helps. Karen Gringhuis
PS Depending on your clay body, slow bisque may not even
burn out ALL the stuff which causes outgassing & bloating.
Richard Burkett has some thought on this.
Ron Roy on wed 23 jul 97
Hi Joan,
Soaking at the end of the bisque will not help. The problem accurs between
700C and 900C when carbon is released from the clay body. If there is not
extra oxygen around then the Carbon will take Oxygen from the iron in your
clay reducing it to FeO - a strong flux - this in turn over fluxes your
body during the glaze fire. Make sure you go slower between 700 and 900C
and make sure you are not in reduction during that stage of the bisque. You
can tell if there is free oxygen in a kiln by putting a piece of cardboard
or wood in a spy hole - if it burns inside there is free O - if not let
some in.
If there is no iron in your body then we have to look elsewhere for the problem.
>----------------------------Original message----------------------------
>Greetings everyone. Lately i have been noticing more incidences of bloating
>once a piece is fired- small bumps in the clay body only noticeable after
>the glaze firing. This happens both in my wood-fired kiln as well as the
>electric, and at a workshop with Jack Troy, he noted that soaking a bisque
>firing when at temperature will burn out anything that needs to be and
>solve the problem. Trouble is, I didn't ask enough questions, and am
>wondering what others do for soaking. I have an L&L kiln with 4 rings and 4
>switches, and I've just been guessing at the soak length and how many
>switches to leave on for how long. So, if anyone can give me advice on the
>fine points of a bisque soak I'd appreciate it. Do you leave all switches
>on but set at low? Or just a couple of rings going? I do not use a kiln
>sitter, just cone packs in there, and want to avoid spending money on more
>equipment to measure temperature. I guess the big question is how long it
>takes to burn out the bloating bugs and to do it but not overdo it. I'd
>also be interested in hearing what people do when soaking a glaze firing-
>again- how many switches, set where, and for how long, and what the
>advantages are . i have heard glazes are "richer" and more beautiful whan
>they are soaked, but wonder technically why and if people have found that
>to be true. (Not talking about crystalline process) So thanks in advance
>for any help out there!
Ron Roy
Toronto, Canada
Evenings, call 416 439 2621
Fax, 416 438 7849
Studio: 416-752-7862.
Email ronroy@astral.magic.ca
Home page http://digitalfire.com/education/people/ronroy.htm
James Dapogny on wed 23 jul 97
Dear Joan,
I can't tell you anything about soaking in an electric kiln since we fire
bisque in a gas kiln. But it might help to tell you that we soak in the
bisque firing for approximately an hour between 1450 and 1500. The ideal
temp is 1470 or so since this is when the carbon is burning out, as I
understand it. Anyway, I think that we accomplish something by holding at
this range. We do it in our gas kiln by turning back the gas and air to
the starting point (by this time, we have had 3-5 turnups, so we are
turning back the same number). Hope this is of some help.
--Gail Dapogny in Ann Arbor
stevemills on wed 23 jul 97
Dear Joan,
Here in the UK we have many clays which are pretty impure to say the
least. Our bisc regime is to fire slowly with the hole in the lid of the
Kiln(that's a UK modification) open right through the firing. With solid
lid Kilns I would leave the top spy hole open and fire very slowly. If
soaking; on a scale of 1-7 (7=high) on our Olympics I set the heat input
at 4.5 and soak for about 40 mins or until I can't smell the burn-off.
We do this by catching it at the finish, over-riding the Kiln- sitter,
and setting the limit timer for approx 40 mins.
Steve
In message , The Slack-DeBrock Family writes
>----------------------------Original message----------------------------
>Greetings everyone. Lately i have been noticing more incidences of bloating
>once a piece is fired- small bumps in the clay body only noticeable after
>the glaze firing. This happens both in my wood-fired kiln as well as the
>electric, and at a workshop with Jack Troy, he noted that soaking a bisque
>firing when at temperature will burn out anything that needs to be and
>solve the problem. Trouble is, I didn't ask enough questions, and am
>wondering what others do for soaking. I have an L&L kiln with 4 rings and 4
>switches, and I've just been guessing at the soak length and how many
>switches to leave on for how long. So, if anyone can give me advice on the
>fine points of a bisque soak I'd appreciate it. Do you leave all switches
>on but set at low? Or just a couple of rings going? I do not use a kiln
>sitter, just cone packs in there, and want to avoid spending money on more
>equipment to measure temperature. I guess the big question is how long it
>takes to burn out the bloating bugs and to do it but not overdo it. I'd
>also be interested in hearing what people do when soaking a glaze firing-
>again- how many switches, set where, and for how long, and what the
>advantages are . i have heard glazes are "richer" and more beautiful whan
>they are soaked, but wonder technically why and if people have found that
>to be true. (Not talking about crystalline process) So thanks in advance
>for any help out there!
>Joan Slack-DeBrock/River Run Pottery
>P.O.Box 95
>McNaughton, WI 54543
>715-277-2773
>riverrun@newnorth.net
>
--
Steve Mills
@Bath Potters Supplies
Dorset Close
Bath
BA2 3RF
UK
Tel:(44) (0)1225 337046
Fax:(44) (0)1225 462712
Carol Jackaway on thu 24 jul 97
Hi,
I have a Econo electric kiln my firing method is this: all switches on low
for 1 hour
All
switches on med. fro 1 hour
All
switches on high for 1 hour
The lid and spy holes are open till the last hour then i close up all put
the last spy hole and lid. Leave these open 1 more hour on high then close.
Now this is on my kiln and I beleive all jkilns are different. The best
thing to do is make a cone pack for each ring, fire the kiln, make sure your
bottom ring is reaching temp. as the top. If your cone packs are on target
then its just your soaking. I have also seen blistering due to impurities
and over firing.
CoilLady@aol.com
Carol
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