liz gowen on thu 12 nov 09
Chris I think you hit on the head one of the problems. The distance =3D
between
the shelves and the outside of my kiln is about 1 1/2 inches. I have =3D
been
unable to find in any of the books I had how much space was needed. I am
thinking for the next firing to make it only one shelf wide to see it =3D
that
lets the heat rise better. Can there be too much space?. I then may =3D
consider
having the shelves cut down to 10x20. I think the 12x24 are just too big =
=3D
for
this kiln. Other question how far from the flame do you put your first =3D
shelf
or how far from the bottom of the kiln. I raised it up 12 inches on one =3D
side
and 15 on the other to stagger the hieght and am hoping it could go =3D
lower
especially with the only 1 shelf wide.
As far as checking for leaks I did this last time and filled in a =3D
lot of
areas with fiber where needed. I may need to figure a way to do =3D
something to
the angle iron at the flue opening, maybe cover with carved out soft =3D
brick
to tighten it up but still be able to move the damper. Thanks for your
input. Gives me some ideas to try next....Liz
-----Original Message-----
From: Trabka, J Christian [mailto:Christian.Trabka@dematic.com]=3D20
Sent: Tuesday, November 10, 2009 8:22 AM
To: elgowen@verizon.net
Subject: 3rd copper red firing
Liz,=3D20
I've had 2 kilns a small updraft (12 cubic feet) and a larger downdraft =3D
(32
cubic feet - MFT). In looking at your blog. It appears that yours is =3D
like my
first kiln, a smaller updraft. I've only had 1 gas kiln (used for both =3D
the
bisque and glaze firing). Both kilns used venturi burners. I see in your
blog that the primary air intake is somewhat closed (I always allow as =3D
much
primary air into the burner as possible). I want the burner to always be =
=3D
as
efficient as possible; using gas pressure (or a damper) to switch =3D
between an
oxidation and reduction atmosphere. I look for a nice blue flame all the
time. With an empty kiln, the door open and dim light, light the =3D
burners.
Use the amount of gas that you would expect to use during the middle of =3D
the
firing. Look at the flame. The flame tip should look like a bunch of =3D
sharp
random height pencils - not like a candle flame.=3D20
My current kiln, a MFT, has 12 Geil natural gas burners. In the bisque
firing I always have an oxidation atmosphere (0.03 to 0.04 on my =3D
Oxyprobe).
The damper is set at 5-inches of opening and the gas is set at 2-inches =3D
of
water column. For my glaze firingsI have a reduction atmosphere (6.3 on =3D
my
Oxyprobe). The damper is set at 5-inches of opening and the gas is set =3D
at
3-inches of water column (depending on the weather and the loading of =3D
the
kiln I make minor adjustments on both the damper setting and the gas
pressure).
Over the years of firing both kilns I note that during an oxidation =3D
firing
the top of the kiln gets hot first and during a reduction firing the =3D
bottom
of the kiln gets hot first.=3D20
It is important in both firings (glaze and bisque) that there is space
between the kiln shelves and the side of the kiln for the heat, air, and
flame to move. You do not show the stacking of the kiln just before the
firing. In my current kiln there is 9-inches between the shelf and the =3D
side
of the kiln. How much room do you leave for the atmosphere to move =3D
inside
the kiln and across the shelves?
A suggestion for the next time you fire the kiln is to schedule the end =3D
of
the firing to be when it is dark outside. Look at the kiln and see where
heat is escaping (what parts of the fiber is red, are there long seams =3D
that
show a red tinge? Can you see flames leaking out of the kiln? What does =3D
the
flame look like coming out of the chimney (you can see mine on my =3D
facebook
page).
I hope that these thoughts help. It took me 2 years of trial and error =3D
(with
a detailed log book) to get my copper reds.
Chris=3D20
liz gowen on thu 12 nov 09
Bill, Thanks, went back to look at your site. I will try the shelf at =3D
the
top several inches from the exit flue. I did stagger the shelves hoping
this would improve heat flow but think I need more space betwwen the =3D
side
walls and the shelf. Currently there is only about and inch and a half. =3D
I am
having a hard time in my books finding how much space is needed , too =3D
much
,too little also the amount of space from the flame. I was thinking of
trying 1 shelf wide which will leave a lot of space for the next firing =3D
but
not sure if going to 10 by 20 shelves instead of 12 x 24 might =3D
eventually
work. You mention I think about 4 inches of space on the bottom is this =3D
four
from the floor or four from the flame ( a little nervous about melting
another shelf.) Is there a higher temp shelf I could use on the bottom =3D
than
the clay shelves? Liz,
Took a look at your blog and was going to ask about pictures of how the =3D
kiln
was stacked, then I looked down the page and realized this is an updraft
kiln, so you will have other issues to even out the heat than with a
downdraft kiln. And how you load this kiln may be very important.
You'll want tight load at bottom, lighter up top.
I would also suggest leaving a space between the two shelf stacks, like =3D
an
inch gap.
Stick with the lower gas pressure for the firings.
I'd also make marks for the damper 1/4" apart as just a little change =3D
can
make a big difference.
You may also find placing a piece of broken shelf, about same size as =3D
flue
opening, about 2" below the opening inside the kiln may help with some =3D
back
pressure to slow escaping gases and more even temperatures.
Read about what I had to do to get my updraft to even out on my web =3D
site.
Bill
--=3D20
William "Bill" Schran
wschran@cox.net
wschran@nvcc.edu
http://www.creativecreekartisans.com
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