Lisa E on wed 6 dec 06
Hi There;
I thought that all water was burned off at 212F and I have been bringing the
temp up slowly until after that point, then I start to speed it up until
cone 06. After 212F, I close the lid and peep holes (2 of them, my kiln is
18" square inside).
What I noticed was between 900 - 1100F I see a lot of steam. I just found
out that that is when all the chemically bound water is released.
1) Should I have the top peep open to let the steam out at this point?
(Note all the pieces were dried for 3 or more weeks)
2) Should I slow down the temp between 900 - 1100F to not cause stress on
the ware?
3) As I am reaching temp, should I start to slow down the temp? I do this
with glaze firing but should I also do it when bisquing?
4) Once I reach temp and my cone bends and I turn off the kiln, should I
leave the peeps open or closed or does it matter? I lost my first piece
today (but it was huge and coil-built so I had my doubts) and I think I
heard it crack at the very end when I took the peep out. Could it be
because the cold air rushed in????
Thank you in advance!
--
Lisa E
Sunny Daze Design Pottery Studio
Squamish, BC
WJ Seidl on thu 7 dec 06
Lisa:
Go online and read about quartz inversion.
Best,
Wayne Seidl
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Lisa E
Sent: Thursday, December 07, 2006 12:19 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Bisque Fire Steam
Hi There;
I thought that all water was burned off at 212F and I have been bringing the
temp up slowly until after that point, then I start to speed it up until
cone 06. After 212F, I close the lid and peep holes (2 of them, my kiln is
18" square inside).
What I noticed was between 900 - 1100F I see a lot of steam. I just found
out that that is when all the chemically bound water is released.
1) Should I have the top peep open to let the steam out at this point?
(Note all the pieces were dried for 3 or more weeks)
2) Should I slow down the temp between 900 - 1100F to not cause stress on
the ware?
3) As I am reaching temp, should I start to slow down the temp? I do this
with glaze firing but should I also do it when bisquing?
4) Once I reach temp and my cone bends and I turn off the kiln, should I
leave the peeps open or closed or does it matter? I lost my first piece
today (but it was huge and coil-built so I had my doubts) and I think I
heard it crack at the very end when I took the peep out. Could it be
because the cold air rushed in????
Thank you in advance!
--
Lisa E
Sunny Daze Design Pottery Studio
Squamish, BC
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Taylor Hendrix on thu 7 dec 06
Lisa,
This is my opinion:
1) I have all peeps out and lid propped open as long as possible. For
me that is just about when I start to see color in the bottom peep.
Coinsides with my next to last turn up?
2) If you are not getting signs of stress from your bisque, no need to
change. My bisque is a standard Paragon bisque for three-way switches,
but I am going to be slowing down my bisque in the future. Slower
bisque, better bisque.
3) I do not attempt to slow down the last hundred or so deg in my
bisque. I do not see a need for it, but if this is how you want to
slow down your bisque, it might be fine. Again, slower bisque, better
bisque.
4) I close up all peeps once endpoint is reached. I do not want any
stray draft entering kiln and dinking my pots. I see no need to open
them up because I see no justifiable need to speed cool a bisque kiln.
Quartz dunting sucks.
I fire an electric, three-way switch, 7 cuft Paragon and have been
potting for aprox. 4 years. Thus ends the full disclosure.
Taylor, in Rockport TX
Bruce Girrell on thu 7 dec 06
Wayne, Lisa
Though the quartz inversion happens at a similar temperature, quartz
inversion does not release steam. The steam comes from dehydroxylation of
the clay, the removal of what is sometimes called "chemical water".
Bruce Girrell
Snail Scott on fri 8 dec 06
At 09:18 PM 12/6/2006 -0800, you wrote:
>What I noticed was between 900 - 1100F I see a lot of steam. I just found
>out that that is when all the chemically bound water is released.
>1) Should I have the top peep open to let the steam out at this point?
>(Note all the pieces were dried for 3 or more weeks)
I generally bisque with a peep open all the way
through the firing, since I have no kiln vent.
>2) Should I slow down the temp between 900 - 1100F to not cause stress on
>the ware?
I've never seen the need. Most electric kilns
just don't fire fast enough to be a problem.
>3) As I am reaching temp, should I start to slow down the temp? I do this
>with glaze firing but should I also do it when bisquing?
Slowing down for a glaze fire is to allow the
melted glaze minerals to blend and interact
more thoroughly. It's not necessary for a bisque,
since nothing is fluid and melted. It is good
to have a nice long bisque firing, though, so
if you get to peak temperature pretty fast,
soaking at the end will serve that purpose.
>4) Once I reach temp and my cone bends and I turn off the kiln, should I
>leave the peeps open or closed or does it matter?
It seldom matters, but putting it in is
best. (One out at the top is enough during a
bisque firing; you don't need all of them out.)
>...I lost my first piece
>today (but it was huge and coil-built so I had my doubts) and I think I
>heard it crack at the very end when I took the peep out. Could it be
>because the cold air rushed in????
Do you mean at the end after cooling, or
at the end of the heating process?
Bisque is usually not very vulnerable to
thermal shock, but if the piece had stresses
due to uneven drying, etc, that little
bit of added stress could have been the last
straw. If so, then it probably would have
cracked in the same place eventually anyway.
Most of my own work is huge and coil-built;
it needn't be a recipe for disaster at all.
Making sure your coils are well-joined is
important, though, and that they all go on
at the same level of moisture. If it cracked
along a joint line, that was likely the true
problem, and the cold air from the peep just
revealed the weakness. Better then, than
after you put a lot of work into glazing and
refiring!
Personally, I see very little evidence that
quartz inversion is a significant factor
in cracked bique.
-Snail
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