Lorraine Pierce on sat 6 oct 01
----- Original Message -----
From: mel jacobson
To: Lorraine Pierce
Sent: Saturday, October 06, 2001 1:16 PM
Subject: Re: Fw: Gas-electric kiln
> yes, you can send it.
>
>
> At 12:46 PM 10/6/2001 -0400, you wrote:
> >Mel if this is too long for the list, please advise...or if I should
phone
> >you? Thanks, Lori P.
> >----- Original Message -----
> >From: Lorraine Pierce
> >Sent: Saturday, October 06, 2001 12:24 PM
> >Subject: Gas-electric kiln
> >
> >
> > > Here we go Mel and Nils,
> > >
> > > and all those interested in gas-electric kiln conversions...I have
gone
> > > from shock, it seemed so bad when I first opened the kiln, to the
> > > realization that there is some great info there...I just have to learn
how
> > > to use it!
> > >
> > > My converted kiln is a Skutt 27 fired with electricity and a pipe
burner,
> > > hooked up to a propane tank. Two inch hole in double base for burner
port
> > > and the same in the lid for the soft brick damper. Burner head a scant
> >inch
> > > below the kiln base. A small cone 10 in the sitter (no computerized
> > > controll), and three large cone packs to monitor lowest shelf, center
and
> > > top heat. Reducing atmosphere was monitored visually by back pressure
at
> > > ports and later comparisons were made between the same glazes fired in
> > > different parts of the kiln. I also used a non-digital pyrometer
placed in
> > > the center peep hole. The half kiln shelves were staggered to create
> > > atmospheric turbulence as I understood from reading Clayart, the first
> >shelf
> > > on two inch postsfrom the kiln base, its 'other half' on four inch
posts
> > > repeated in varying heights til the kiln was loaded. No piece of shelf
,
> >or
> > > full shelf was placed above the burner port, thus no bag wall was
created
> > > and flame impinged on pots at the inner shelf edges, causing blackened
> > > bubbling of some glazes on the inner shelf sides.
> > >
> > > First, for anyone with experience in an average sized studio gas kiln
of
> > > hard brick vintage,(me), this experience is very different. I am sure
> >those
> > > firing a studio sized soft brick kiln in gas reduction would also find
the
> > > small poorly insulated electric kilns converted to gas-electric very
> > > different. So much is going on in a small space. In an effort to
learn as
> > > much as possible, from which commercial clay took reduction best ( to
my
> > > liking), to which glazes worked best for me in this situation, I had
an
> > > abundance of tests on each shelf. More than thirty mice in all, and
> >several
> > > pots dipped in each test glaze so that each glaze and clay body was
tested
> > > in each part of the firing.
> > >
> > > My conclusions are that the pipe burner has too large an orfice. (1/8
").
> > > When we first lit the burner for a test run, nothing in the kiln, 2
1/2"
> > > pressure, we had a bush of flame about 30''high by 24" wide coming
from
> >the
> > > top of the kiln. After loading and introducing the gas at 1650 F the
gas
> > > could not be cut back low enough to reduce the back pressure at the
ports
> > > below three-four inches. We had to maintain almost 1 psi to keep the
> >burner
> > > from going out.
> > >
> > > The kiln sitter popped off (small cone 10) with a pyrometer reading of
> > > 2100F. I thought it must be heatwork from the gas. Or a defective
> > > pyrometer. Large cone ten starting to bend in the top, nine full down.
I
> > > later found cone10 fully down on the bottom shelf tho not melted, and
the
> > > sitter cone 10 in a full U. The good reduction in the bottom section
> > > decreased to none on the top level even tho there had been about three
> > > inches of back pressure at the top port. The reduction was also spotty
> >even
> > > where some was good. Pete's Red was a grey bubbly mass with centers of
red
> > > in the broken bubbles and glaze 'blown off' the pots. Perhaps it is
not
> > > blown off but there are gaping holes in the glaze. For many glazes it
> >seems
> > > the kiln had cooled much too fast, leaving visual pinpricks on the
> > > surface,as well as some mat glazes not matured at all. I had opened
the
> > > peeps, lid hole and not covered the burner port, to 'leave it open to
> >clear'
> > > as Mel suggested, then at 1700 or so closed it up and turned the
electric
> > > back on Medium for an hour. Now I believe the directions meant 'fire
back
> > > up' to ^10, and I should have turned it to High and done so instead of
a
> > > belated soak.
> > >
> > > The firing was 7 1/2 hours til the sitter popped. Some of the old
reliable
> > > glazes were good, Mamo, Rhodes/Hopper 25, 1.2.3.4, Tenmoku, some
celadons,
> > > (the best red was from a pot dipped in Pete's Red that flashed onto a
> > > 1.2.3.4 celadon test!) Perhaps while learning my kiln I should test
with
> > > glazes that mature from ^8-10, or put a ^11 in the sitter. Some whites
as
> > > well as the red had trapped carbon, and were grey and ugly and lumpy.
> > >
> > > I think I need to slow my firing down and hold it to even out the heat
and
> > > atmosphere, therefor I will have my pipe burner drilled out and fitted
> >with
> > > changeable orfices. I need to check my pyrometer against a known
accurate
> > > one. I am tempted to use some glazes with a broader firing range, but
then
> >I
> > > would not get as clear a story as I will if I repeat the same glazes,
and
> > > change only the gas imput. And I wish I had a second lid to double the
top
> > > insulation as I did the bottom. Well, there we are. Mel, Nils, I
hope
> > > to hear from you and also from others who have converted kilns larger
than
> >a
> > > 181. I should sign myself, Newbie...Lori Pierce in New Port Richey,
Fl.
> > >
> > >
> > >
> > >
>
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