Geoffrey Barst on thu 1 dec 05
Recently I have been firing my trash can fiber lined raku kiln with
propane and preheat my pots in the kitchen oven. This is a very cumbersome
procedure and still doesn't address the thermal shock problem entirely as
some of the thicker pieces crack, almost certainly because my raku kiln is
too efficient and the temperature rises too fast. I have a venturi burner
and with the air totally shut down on the burner and the regulator (0-30)
psi just cracked open my pyrometer shows a temperature rise of 200 deg/min
or more. It takes 12-15 min to reach 1900 F with the air fully open on the
burner. Flames come out of the top of the kiln, which my reading has just
told me is wasteful of gas & indicates a much too high pressure setting on
the regulator.
Has anyone thought up a satisfactory preheating system for this type of
kiln? My initial low tech solution (yet to be tried) is a propane brazing
torch stuck through the burner port. Also do I need to buy a lower
pressure regulator and will it then require a different orifice in the
burner?
Geoff Barst
marvpots@juno.com on thu 1 dec 05
Geoff:
I would presume that you bisque your pots before raku firing; in that c=
ase you must have an electric kiln as well; thus, the simplest, and mos=
t effective way of preheating your raku pots is to place them in the el=
ectric kiln using a low temp cone in the cone sitter, and when your raku=
kiln is ready, simply taake the pots out of the electric kiln ( using g=
loves of course) and move the pots to the raku kiln. (some people pref=
er preheating by placing the "next" load on top of the raku kiln; this =
can and does work if you have enough space on top of the kiln and can ke=
ep the pieces away from the flu.)
This works smoothly, and you can set up a rythm: a load in the electric=
kiln; a load in the raku kiln; a load in the reduction can. This will=
keep you pretty busy but will get the job done without the problems you=
are presently encountering, hopefully.
All the best.
Marvin Flowerman,
marvpots@juno.com =
Taylor from Rockport on thu 1 dec 05
Hey Geoff:
I fired a raku conversion kiln with a weed burner several times. The
magic number seemed to be about 12psi for us and that seems high to others
who use venturi. Weed burner has a needle valve for flame control. I'm
not sure why you would need to change the orifice. It is fuel specific as
far as I know.
12 minutes is a pretty fast rocket but I've heard of others gettin' 'er
done that fast. Parhaps those first 500 degs should be taken a bit
slower. stretch it to 20 minutes.
What does the lid look like on your can? Look for flat, stable places
near the kiln (near burner port, flue) where you can set pots. We never
really warmed our pots (raku clay) and had no real problem with breakage.
We were cycling at 30 minutes, however. Does make a difference.
If you have the ability to pots pics, please post some to the web.
Clayart has a couple of people who have started foto logs. I miss my
raku. Someone want to come down to Rockport, bring some ceramic fiber and
help me convert my small Paragon Fastfire to raku? Oh yeah, bring a big
tank.
Taylor, in Rockport TX
http://www.wirerabbit.blogspot.com
http://www.wirerabbitpots.blogspot.com
http://www.clayartmugshots.blogspot.com
On Thu, 1 Dec 2005 16:02:44 -0500, Geoffrey Barst
wrote:
>Recently I have been firing my trash can fiber lined raku kiln with
>propane and preheat my pots in the kitchen oven. This is a very cumbersome
>procedure and still doesn't address the thermal shock problem entirely as
>some of the thicker pieces crack, almost certainly because my raku kiln is
>too efficient and the temperature rises too fast. I have a venturi burner
>and with the air totally shut down on the burner and the regulator (0-30)
>psi just cracked open my pyrometer shows a temperature rise of 200 deg/min
>or more. It takes 12-15 min to reach 1900 F with the air fully open on the
>burner. Flames come out of the top of the kiln, which my reading has just
>told me is wasteful of gas & indicates a much too high pressure setting on
>the regulator.
Andrew Niblett on thu 1 dec 05
hi
i think you need to buy a smaller burner when you reload the pieces after=
a firing let the kiln drop too 250 300degrees
and then place in a small piece of COLD kiln shelf then put the p[iece on=
top of that instead of the hot shelf
hope this helps
andrew niblett england
>-- Original Message --
>Date: Thu, 1 Dec 2005 16:02:44 -0500
>Reply-To: Clayart
>From: Geoffrey Barst
>Subject: Preheating pots for raku
>To: CLAYART@LSV.CERAMICS.ORG
>
>
>Recently I have been firing my trash can fiber lined raku kiln with
>propane and preheat my pots in the kitchen oven. This is a very cumberso=
me
>procedure and still doesn't address the thermal shock problem entirely a=
s
>some of the thicker pieces crack, almost certainly because my raku kiln
is
>too efficient and the temperature rises too fast. I have a venturi burne=
r
>and with the air totally shut down on the burner and the regulator (0-30=
)
>psi just cracked open my pyrometer shows a temperature rise of 200 deg/m=
in
>or more. It takes 12-15 min to reach 1900 F with the air fully open on t=
he
>burner. Flames come out of the top of the kiln, which my reading has jus=
t
>told me is wasteful of gas & indicates a much too high pressure setting
on
>the regulator.
>
>Has anyone thought up a satisfactory preheating system for this type of
>kiln? My initial low tech solution (yet to be tried) is a propane brazin=
g
>torch stuck through the burner port. Also do I need to buy a lower
>pressure regulator and will it then require a different orifice in the
>burner?
>
>Geoff Barst
>
>________________________________________________________________________=
______
>Send postings to clayart@lsv.ceramics.org
>
>You may look at the archives for the list or change your subscription
>settings from http://www.ceramics.org/clayart/
>
>Moderator of the list is Mel Jacobson who may be reached at melpots@pcli=
nk.com.
___________________________________________________________
Tiscali Broadband from 14.99 with free setup!
http://www.tiscali.co.uk/products/broadband/
Christmas gift ideas and festive features - visit the Tiscali Christmas m=
icrosite.
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Frank Colson on thu 1 dec 05
Geoff- I don't know if your raku kiln has a flue opening ontop? ROCKY
RAKU, who does have a 4" opening on top, likes to have as many as 3 or 4
pieces pre-heating around that flue hole, sitting on the lid, waiting their
turn to plunge into the fire chamber. But then, ROCKY goes to 1900 in less
then 30 seconds, so, top sitting pre-heating pieces tend to rotate a lot.
Frank Colson
www.R2D2u.com
----- Original Message -----
From: "Geoffrey Barst"
To:
Sent: Thursday, December 01, 2005 4:02 PM
Subject: Preheating pots for raku
> Recently I have been firing my trash can fiber lined raku kiln with
> propane and preheat my pots in the kitchen oven. This is a very cumbersome
> procedure and still doesn't address the thermal shock problem entirely as
> some of the thicker pieces crack, almost certainly because my raku kiln is
> too efficient and the temperature rises too fast. I have a venturi burner
> and with the air totally shut down on the burner and the regulator (0-30)
> psi just cracked open my pyrometer shows a temperature rise of 200 deg/min
> or more. It takes 12-15 min to reach 1900 F with the air fully open on the
> burner. Flames come out of the top of the kiln, which my reading has just
> told me is wasteful of gas & indicates a much too high pressure setting on
> the regulator.
>
> Has anyone thought up a satisfactory preheating system for this type of
> kiln? My initial low tech solution (yet to be tried) is a propane brazing
> torch stuck through the burner port. Also do I need to buy a lower
> pressure regulator and will it then require a different orifice in the
> burner?
>
> Geoff Barst
>
>
____________________________________________________________________________
__
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
Robert W. Anderson on thu 1 dec 05
Geoffrey,
I've got one of those missile launchers. Venturi burner with adjustable
forced air. Able to reach temp...1850...in about 7 min. That's two or
three pots the size of a beer can...no cracks!!! Was foolish...have since
changed my ways. Try preheating the pot in your kiln. Remove cover, use
very low heat...after 5 min or so replace cover and resume your normal
firing. Larger pots, longer preheat. Good luck.
Robert Anderson
rwanaa@charter.net
----- Original Message -----
From: "Geoffrey Barst"
To:
Sent: Thursday, December 01, 2005 3:02 PM
Subject: Preheating pots for raku
> Recently I have been firing my trash can fiber lined raku kiln with
> propane and preheat my pots in the kitchen oven. This is a very cumbersome
> procedure and still doesn't address the thermal shock problem entirely as
> some of the thicker pieces crack, almost certainly because my raku kiln is
> too efficient and the temperature rises too fast. I have a venturi burner
> and with the air totally shut down on the burner and the regulator (0-30)
> psi just cracked open my pyrometer shows a temperature rise of 200 deg/min
> or more. It takes 12-15 min to reach 1900 F with the air fully open on the
> burner. Flames come out of the top of the kiln, which my reading has just
> told me is wasteful of gas & indicates a much too high pressure setting on
> the regulator.
>
> Has anyone thought up a satisfactory preheating system for this type of
> kiln? My initial low tech solution (yet to be tried) is a propane brazing
> torch stuck through the burner port. Also do I need to buy a lower
> pressure regulator and will it then require a different orifice in the
> burner?
>
> Geoff Barst
>
>
____________________________________________________________________________
__
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
>
>
> --
> No virus found in this incoming message.
> Checked by AVG Free Edition.
> Version: 7.1.362 / Virus Database: 267.13.10/189 - Release Date:
11/30/2005
>
>
Marcia Selsor on thu 1 dec 05
Dear Geoffrey,
I don't preheat most of my raku nor the work of participants at
workshops in Montana. I make sure we glaze the day before.
For little things, I can set them on top of my hardware fabric fiber
kilns...but I usually don't bother. We lost one piece at Red lodge
this past summer at my annual workshop there and that was from a bead
rack breaking. For my big slabs, I let the kiln cool down a few
minutes before setting them on the shelf. Then I leave the chamber up
for a little while longer before bringing it down and turning on the
burners. I have 2 for my bigger raku kiln. I don't get what your
setting is..what is 0-30? And don't know what kind of burner you are
using.
I run on 2.5-3 psi. I don't use a lot of gas either. When I fired a
wood raku kiln, the pots were preheated on top of the fire box. We
split 2x4s into small pieces and stoked those.
Towards the end of the day, the firing would go really fast. One
batch went to melted glazes in three minutes...of course that was not
the case all day long, but a good bed of coals really made that kiln
fly. It was a 55 gallon fiber lined barrel on a pulley system. The
barrel sat on a brick beehive and the fire box was about three feet
long.. I have a drawing of it in Steve Branfman's Raku book, 2nd
edition. That was fired from 1975-1980 in Billings. Then we moved the
ceramics program and I had the raku kiln nearer to the building. We
eventually went to a gas hookup. I miss the fuel gathering trips and
the day long firings up on the hill. Outdoor firings are fun. In
Montana it was a Spring ritual!
Marcia Selsor...in cold snowy Montana
On Dec 1, 2005, at 2:02 PM, Geoffrey Barst wrote:
> Recently I have been firing my trash can fiber lined raku kiln with
> propane and preheat my pots in the kitchen oven. This is a very
> cumbersome
> procedure and still doesn't address the thermal shock problem
> entirely as
> some of the thicker pieces crack, almost certainly because my raku
> kiln is
> too efficient and the temperature rises too fast. I have a venturi
> burner
> and with the air totally shut down on the burner and the regulator
> (0-30)
> psi just cracked open my pyrometer shows a temperature rise of 200
> deg/min
> or more. It takes 12-15 min to reach 1900 F with the air fully open
> on the
> burner. Flames come out of the top of the kiln, which my reading
> has just
> told me is wasteful of gas & indicates a much too high pressure
> setting on
> the regulator.
>
> Has anyone thought up a satisfactory preheating system for this
> type of
> kiln? My initial low tech solution (yet to be tried) is a propane
> brazing
> torch stuck through the burner port. Also do I need to buy a lower
> pressure regulator and will it then require a different orifice in the
> burner?
>
> Geoff Barst
>
Michael Lancaster on sun 18 dec 05
Geoff,
There are a number of contributing factors for dunting (body cracks) =
which form in your Raku ware. Since you preheat in an oven, I might =
suggest you research your clay body a bit further. After years of my =
'own' clay body, I came across one comercial body I really like: Big =
White from Laguna. This body is so versatile that we have fired it in =
soda at cone 11-12. At Raku temps of 1800-2000, it is a white body. We =
have fired my wife's sculpture at 30"+ heights at thicknesses of 3/8" up =
to 3/4". =20
We do preheat on top of the kiln, but those 25" and up sculptures get =
preheated in the electric kiln. When we start 'cold', we ususally pull =
the burner back from the port and 'candle' the flame, often using bricks =
or adobes to keep the wind from the fire. Most good clay bodies should =
easily allow 15-20 minute firings. However, if it is sculpture, what's =
wrong with a crack? Commercially this may bother some galleries or =
collectors. If you watch the new movie out on Paul Soldner, he =
addresses that. We know we can't ship some large works that may break =
in transit or fall apart when the collector moves it, especially if they =
retail for more than $2,000!=20
There is one more aspect to consider: slow down. Put that work in the =
hot kiln - close it up (maybe leave the flu open), and wait. The heat =
of the shelf, the base bricks, etc.. will preheat your work. Good luck =
and enjoy the fire.
Michael Lancaster
Studio98B
info@studio98B.com
www.studio98B.com=20
Cerrillos, NM
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