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wood kiln (long)

updated fri 31 mar 00


Karen Elkins on thu 30 mar 00


I have two more books you may find useful or just interesting, the first is
from the Foxfire series of books, which are an amazing social documentary.
Number 8 is devoted to Southern American Folk Pottery, "from pug mills
(donkey driven), ash glazes, and groundhog kilns..." the ISBN is
0-385-17741-0 (pbk) published by Anchor Books. It contains many detailed
series of photographs and transcribed interviews with Folk potters talking
about their work, including kiln building and firing.

The second is a book which I think may be out of print, 'Exploring Fire and
Clay' bu Arne Bjorn published by the Van Nostrand Reinhold Company, with
Library of Congress catalog card no. of 72-118559. This is a Danish book in
English translation and describes experiments at the Historical Archaeology
Experimental Center at Lejre, Denmark in the 1960's. The firings range from
an open-pit kiln, a Hasseris and a Glostrup kiln made of wicker and a brick
kiln called a St. Olias, all named after the places these kilns were
excavated. There are firing schedules for each in the book.

As for your firing schedule, I am not a hugely experienced kiln firer, I've
been at and helped fire kilns over the last 12 years maybe twice a year -
but my friend and I did have sole charge of the last kiln we fired, a two
firebox arched kiln (sorry I don't know the proper name for it) standing
about 5ft by 5ft across. The most important time we've found in firing is
the very beginning- the first 4-5 hours, it's crucial that you don't get
rushed by people saying that you're going too slow!

The fire boxes I've used all have iron bars halfway up them, like an oven
shelf, and we start the fire below this, in the dirt on the bottom, so the
heat takes longer to reach the kiln. Also, keep the fire at the front
opening of the fire box, don't let it get too far towards the body of the
kiln. After a few hours when the steam rising off the kiln has started to
fade back and the floor of the fire box is filling with ash and hot embers,
gradually move the fire back in the box, throw the wood further in, the
begin to place some of the wood higher up onto the iron bars.

Vary the size of the pieces of wood you use, through the firing, keep the
wood fairly chunky at the start, give the fire time to burn through it, it
doesn't give off as much heat. Also more ash is made from these bits at the
start, which you want to build up embers.

Let the fire begin to consume the piece you've put on before adding another,
don't get the box chocked up with unburnt wood, and don't be afraid to use a
riddling iron to pull the wood back out of the box if it starts going too
fast. Always err on the side of caution.

The ash and embers in the bottom of the box act as a baffle, slowing the
pull through of air, which is useful at the start, but the box may get too
stuffed with ash mid-way or three quarters of the way through, when you
might feel the kiln slow down, the gradual increase in tempo will stop and
you will feel it's a struggle to push it further. Then you can rake some of
the ash out to improve the flow of air. If you haven't been waiting for the
fire to begin to consume the last peice of wood you put on, the box will
choke up with un-burnt wood and too much ash as well. It begins to really
feel like you're feeding this fire in the truest sense, it gains a rhythm of
it's own.

Do you have spy holes? bricks placed end on that you can pull out and look
inside? You will know when you reach red hot heat that you're past the need
to take it slow and can begin to push the kiln higher to reach orange and
yellow to melt your glazes. Then you'll have trouble keeping up and will
want to have plenty of small kindling sized pieces of wood which will almost
vapourise as you throw them to the back of the fire box. If towards the end
you put too much timber on for the kiln to consume through the fire box, you
will see a cone of flame extend from the chimney, which is the kiln reaching
for extra air. This will cause reduction, or burning the kiln with no air
inside, and makes the pots nice and black (depending on your opinion). If
you don't want this, temper your feeding and pull back the wood you just put
on till the cone goes.

Soak the kiln by keeping it at the heat you need to melt the glaze with a
constant check on how the wood is added, just add enough, don't push higher
by feeding, perhaps add some slightly thicker pieces to give it something to
chew on. The ash and embers give you enough heat to be able to pause while
you look in the spy holes - make sure everyone knows not to add fresh wood
while you're looking in or you'll end up minus a eyebrow!

When you're sure you've finished, wait for the fire in the boxes to die down
a little, then block up the box with bricks and cover the chimney while the
embers are hot and nicely glowing, before cold air starts being drawn in to
crack the pots. We seal and cover our kilns with daub (mud, straw & dung
mixed) then leave for 2-3 days.

Overall, we've fired on a schedule of 4-5 hours creeping along, perhaps 8-9
hours mid tempo, and 3-4 hours of what we in the UK call 'welly' as in 'give
it some welly' a term related to labourer's wellington boots meaning
exerting extreme force! When we've fired a larger kiln taking 24 hours to
fire, we extend each of these periods to suit.

I hope I haven't taught you to suck eggs, and there's probably loads I've
skipped over, all that's really important is taking it slow at the start. In
all the firings I've been at, we've never had any breakages, although we did
melt the floor of the new kiln the first time we fired it and all the pots
got embedded in the bricks, but thats another story.

I owe all this experience to Jack (Pete Brown) and Comphrey (Anthony
Forsyth) from around Bath, England, and fired most of the kilns at Kentwell
Hall, Suffolk, England, as a living history volunteer.

I can almost smell the wood smoke....
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