Peter Jones on tue 29 sep 09
I am trying to locate info about building a gas fired, fiber, glaze-test
kiln. I already have a small fiber kiln which I love for doing small, qu=
=3D
ick
turnaround firings, but I am looking to build a mini-kiln just for glaze
tests. I've made some in the past from IFB but want to build a fiber one=
=3D
in
its place. My 15 cu ft fiber kiln goes from room temp to cone 10 in six
hours, making it a breeze to fire and very inexpensive on gas. A fiber
mini-kiln could be fired for practically nothing using a bunsen burner, a=
=3D
ll
of which I have on hand. I have a bunch of 10" x 15" x 1/4" silicon carb=
=3D
ide
shelves which I would use two of for stacking in the firing chamber. My
thought is to build a bent wire frame using hardware cloth (woven steel
mesh) as the outer structure for the kiln, line it with 2" of high temp
fiber and place a layer of fiber under the kiln shelves as well, creating=
=3D
a
total fiber box around the shelves. The question is the placing of the
single burner and the vent on the opposite side. Any suggestions on
positioning, location, staggering of the two shelves for gas flow, etc? =
=3D
Any
suggestions are greatly appreciated.
I realize that firing in a test kiln will not yield the same results as i=
=3D
n a
large downdraft kiln. However, I just had a dependable glaze go to hell =
=3D
in
a hand basket in my last firing. A good, dependable Chun based glaze wit=
=3D
h
cobalt carb and rutile that gave a nice textured blue color wound up comi=
=3D
ng
out black, and I do mean black. It's not the cobalt carb or the rutile a=
=3D
s
they have been with me for over a year with no problems. The one ingredi=
=3D
ent
which I think is the culprit is Gerstley Borate. GB has a long reputatio=
=3D
n
of being extremely variable from batch to batch (50 lb bag to 50 lb bag).=
=3D
=3D20
It's the only new bag of ingredients that I used in this batch of glaze.=3D=
20=3D
Why it should have turned the glaze black is beyond me as all it really
should have done would be to change the gloss or opacity of the glaze, no=
=3D
t
the color. The reason I want to build a small test kiln is that I don't
want to open up the next firing and find a whole kiln load of black pots
when they should be gorgeous copper reds, rutile blues and teal greens, a=
=3D
ll
of which also use GB in the formula, albeit slightly different from the C=
=3D
hun
base glaze that came out black. I also don't want to have to wait until
next month to find out if my new glaze tests work. My big kiln is a 100 =
=3D
cu
ft down draft and will hold a month's worth of labors in it.
Several years ago, I bought a 50 lb bag of dark rutile. What I found aft=
=3D
er
months of watching my rutile blue glaze get worse and worse to the point =
=3D
of
being completely unusable was that that bag of rutile ("welding rod
titanate") had a deflocculant added to it for some unknown reason. My mi=
=3D
xed
glazes would just sink to the bottom of the bucket after stirring
constantly. Dipping pots in the glaze required constantly turning them
around and around to keep the glaze from running off the pots. I tried
calcining the rutile to burn off the deflocculant which only made matters=
=3D
worse. It was enough to make me literally want to give up as a potter, t=
=3D
his
after 36 years at it!!! Needless to say, I don't want to go through that=
=3D
again due to one bad bag of ingredients. Alas, potters are the last stop=
=3D
on
the minerals delivery train and we get what the bigger industries scoff a=
=3D
t.
Caveat emptor/buyer beware....
Hope someone has some ideas of where the problem comes from in the glaze =
=3D
and
how to build a better test kiln/mouse trap.
Thanks,
Peter Jones
Mountain Street Pottery
Camden, Maine
pjcaver@gwi.net
douglas fur on wed 30 sep 09
, Peter Jones
"I am trying to locate info about building a gas fired, fiber, glaze-test
kiln.
1. using a bunsen burner I have on hand.
2. I have a bunch of 10" x 15" x 1/4" silicon carbide shelves
3. line it with 2" of high temp
4. placing the single burner and the vent on opposite sides. "
I re-arranged what you wrote- I think you have all the info you need.
Hank can tell a good story (In the archieves) about the danger of using mes=
h
enclosures for fiber kilns (with back-pressure, as when you're reducing, ho=
t
gasses can pass through the fiber burning you or...)
I made the shell of my test kiln with home-made castable (perlite, sand,
Portland Cement, fireclay approximately 4:2:1:1/2 parts by volume).
From my misadventure with my kiln trying to re-write history(making burners
and refractories that crack and fall apart) I can only say "keep it simple"
for the burner and flue. "burner and vent on opposite sides" says it. Wit=
h
more than one burner to keep it even, updraft is a clear choice. With one
burner I'd be tempted to try a down (cross) draft.
drb
Seattle
I think in brick modules so the shelves suggest to me an 18" cube
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