search  current discussion  categories  kilns & firing - misc 

fast fire confusion

updated sat 8 oct 11


mel jacobson on wed 5 oct 11

i have been reading all the posts about firing
and it does seem that my early posts about
efficient firing has turned into `fast firing`.
there is a huge gap here.

because my small stoneware kiln fires in four and half to five
hours does not mean it is a `fast fire kiln`.
that is the time frame for a very efficient small kiln.
i could stretch that out to 8 hours and the pots would
be the same. the pots from that kiln made by dozens
of potters, with a huge variety of glazes are mostly
`RACERS` of the first order. you should have seen the
pots that david mcbeth from Tennessee took from that kiln.
temmoku with gold flecks that would stand with any pots
i have ever seen. fast fire....??? no...perfect fire.

my big kiln fires in 9-10 hours. it too is a very efficient
kiln. like ron roy, i have a rather low pressure system
of natural gas. it is, what it is.

the burners at the farm are nils lou, very, very powerful
propane burners. they are rockets. they fire half on when
used in the small kiln. at full the back pressure would
be twenty inches.

what i am proposing, over and over is very efficient use
of fuel, having an early infusion of power and energy in the
early stages of firing to save the insulating factor of your brick.

my biggest concern is long warm 8 hours of
pre/fire that wastes fuel and destroys the K factor of your brick.

how long any well made efficient kiln takes to fire has many
factors. type of ware, amount of shelves and posts, loading
of the kiln, stacking issues. and, of course `weather and wind`.

this does not have to morf into a great science discussion. it is
easy observation and knowledge of your kiln. it just makes sense
to get energy into the kiln in the early stages. build that energy
as fast and perfectly as you can. there is no logical reason to
nurse a fuel kiln. hours of warm up...slow increase in temp. it
is plain silly old time 1950's dogma on firing. it was wrong then,
and it is wrong now. i don't fast fire. i fire efficiently. each kiln
will have its own time frame for the cone you
select. some are made so poorly that they can
barely make cone 10. i have seen many of look and
i can say for sure....`this is a twenty hour kiln`...`hey mel, how
did you know?`
crap chimney with enough gaps that it will not pull anything.
a heat dam stack of brick in front of the burners. god, take that
bag wall out.
shelves stacked next to each other. no air spaces.
oversized shelves that almost touch the sidewalls of the kiln.
a kiln stacked so full of pots that no energy can flow through
the kiln.
burner placement that makes the energy flow right up the stack.
long slow start up.
in other words, the most inefficient kiln one can have.

and it always amazes me how folks can be `eco-FRIENDLY` and not have
a clue about the waste of fuel in their own kiln. `oh, that is ok,
i really like my 24 hour firing...and what i get for glazes.`
BS. they don't know how to fire a kiln. period.

it always amazes me that on one hand we have raku that is fired
as fast as can cracks, well made pots and no one blinks
at the time fired. ten minutes? it works fine.
and, we know the clay and glaze is made for raku, but why
do we have to nurse well made, bisque fired pots in a stoneware
firing???? makes no logical sense.
well, except that is how they learned to fire at college in 1966.

all my posts are about `EFFICIENT FIRING` in a well made, well
stacked, safe kiln.

learn your kiln through a variety of firing cycles. try things, make
changes and see what the kiln will do. many start firing one way
and that is it for twenty years. your kiln may be a trans am, and
you fire it like a model T.

from: minnetonka, mn
clayart link:

Ric Swenson on wed 5 oct 11


In grad school...with F C Ball and Fred Olsen...on Carleton's last day befo=
re 'RETIREMENT' from teaching at Univ. of Puget Sound in Tacoma....USC, Mi=
lls, Illinois, etc..... ( actually he taught for many years after that ) w=
e made four wood fired day..... that fired into a single stack/=
chimney. a trick brick at the base of each stack's chimney.........We fir=
ed all of the four 16 Cubic kilns within a day....wood fired ....and fast. =
we got to 4 hours and cone 10 in each kiln. Beautiful.

'Freddy fast-fire got to town...4 hours later cone 10 s down' I wrot=
e in 1976.

Timing of the stoking....small split wood from local plywood factories. Pa=

Champagne and salmon campfires probably helped with the fired produced w=
ares. Fred Olsen watched and directed the stoking from his lawn chair...alo=
ng with some scotch... The wood firing was the best I've seen in 40 years..=
many pieces I showed later in my solo show at the Anchorage Museum.

fast fire can work well. Efficient is fast too. Saves fuel.

We once -fired 10,00 pieces a week at Bennington Potters in fast fire tunne=
l ..propane.....all once bisque at all ....( 7 hours cold to co=
ld) for many years....learning curve was a bit long...but it worked...for t=
wenty years. Made millions in 1980-90s.

My own Olsen 24 kiln kit...which I built myself... over a 27 hour period in= still firing....for Kris Bliss in Anchorage...30 + some years l=
ater. soft brick...sprung arch..nat gas fired. Candle was pilot fire for =
a few hours...then 8 hours to cone 10...cooled another 8....or 10 hours....=
even....firings and as expected from the start.

see my CM article on "Selecting and Designing a Studio" which took me 3 yea=
rs to research and write. CM Jan.1981. which followed CM article Dec.1979=
article on kiln ventilation.
'An inexpensive studio sink trap'... Dec 1978 CM...and so on. 1,000 sq ft=
. I had a three car garage area ...big doors... nice individual space for =
ceramics and painting.

I have had several studios...the best was 1000 sq ft (three car size) stud=
io in Anchorage (ask for details of CM article off line) Chalked off spaces=
on the cement floor and designed the work spaces for drawing/ throwing/tri=

Did a lot of planning on paper...months...years....

Wish I had not moved to Vermont...Big mistake. My studio in Anchorage was =
my best....

"But ...never look back."... as Satchel Page said..."you never know what mi=
ght be gaining on you"....

I made all the wood work myself.....honed my wood working skills......mad=
e teak wood ribs.....made my own ball mill from the motor of an old washing=
machine....made batts for drying slurry.. ..Alaska water pipe heating in t=
he plaster. no need for a pug mill. Used an old roll-away bed into a glaz=
e station.

" invention is the mother.... " I mel has said....make it your=
self....learn from the making.

Now in China for 6 years...once firing bisque. Life is eas=
y here...60,000 potters work here...division of labor...this guy
is guy glazes...this guy fires. Pay a small fee. simple life. I do what I=
want to do myself and leave the rest to the other pros. Now I have 60 squ=
are meters space to myself...nice space....outfitted by the Korean Govt 10 =
years ago....and added to by me in the last 3 years... new wheels...shelves=

do as you need...and want to do...

Just had my solo show in JinagMen City. Very successful. The gallery owner=
paid all expenses...4 star, catalog, food, wonderful Canton=
ese.... fish, donkey, goat meat..unusual...but good stuff.

Life goes on...learn more...

good potting...


Richard H. ("Ric") Swenson, Teacher,
Office of International Cooperation and Exchange of Jingdezhen Ceramic Inst=
TaoYang Road, Eastern Suburb, Jingdezhen City.
JiangXi Province, P.R. of China.
Postal code 333001.

Mobile/cellular phone : 86 13767818872


> Date: Wed, 5 Oct 2011 06:39:52 -0500
> From: melpots2@VISI.COM
> Subject: fast fire confusion
> i have been reading all the posts about firing
> and it does seem that my early posts about
> efficient firing has turned into `fast firing`.
> there is a huge gap here.

Larry Kruzan on wed 5 oct 11

Hi Mel,

As you say the kiln is a system that must work as a system. Chamber, flue,
burners and fuel working together for maximum efficiency, like any other
machine. A car with a 400hp engine that is crippled with a 1" exhaust pipe
is going to run like crap. You have to be able to get the exhaust gases out
of the engine in order to make room for fresh, burnable air.

A 12cf kiln with a 9" square flue is not going to fire right, all the heat
is going to be sucked right up the flue. Likewise a 100cf kiln with a
4.5"x9" flue will be stagnant at much over bisque temps, but that's a
perfect size for my high efficiency 48cf kiln.

Is there a correct formula to address how big a flue should be for a given
size kiln? Just how big does the exhaust pipe need to be?

Best Always,
Larry Kruzan
Lost Creek Pottery

douglas fur on thu 6 oct 11

> "Is there a correct formula to address how big a flue should be for a giv=
> size kiln? Just how big does the exhaust pipe need to be?"
I wish some one would do the science on this one. The only thing I've seen
is drived from Matsubayashi's rule of thumb in Leach. (1/4 to 1/5 the kiln
diameter) This was for hard brick so if soft brick needs 5/8 the gas of har=
(per olsen) is the chimney for soft brick 62.5% the diameter or height or
both of a hard brick chimney?

We see plenty of posts which suggest it could be less but I haven't seen a
contemporary rule of thumb.

inquiring minds want to know

Seola creek

ivor and olive lewis on fri 7 oct 11

I think we are forgetting our roots.when it comes to kiln design and
construction. I suggest a little light reading and digestion of "Kilns" by
Daniel Rhodes and "The Kiln Book" by Frederick Olsen, leavened with
"Handbook for Australian Potters", De Boos, Harrison and Smith and "The
Artists Guide to Firing Kilns" by Harry Memmott. Otherwise its folk lore an=
rule of thumb.
We forget to distinguish between kilns that rely on natural draught for the
flow of air into the chamber or force draft to drive fuel. It seems to me
that a forced draft kiln will not require a stack to create a draft. All
that is necessary is ventilation to exhaust the hot flue gas out of the kil=
For a natural draft kiln, Mel's use of spiral steel tube used by domestic
heating engineers lined as he describes. is a good solution well worth
One factor which most authors seem to ignore is the combined area of Fire
Ports. This is the space into which the burner projects fuel. If the gap is
undersize there is always insufficient air flowing into the kiln. At low
flow rates this may not effect heating but it could lead to oxygen
starvation at high flow rates which wastes fuel and stalls temperature rise=
Conversely, if the Fire Ports are over size the kiln will admit an abundanc=
of cold air and it will be difficult to achieve high temperatures.
Looking through my notes I posted (dated 4-25-2000).instructions to Clayart
on developing a firing protocol for an untried kiln.