Age Pottery Firing at Butser
This is a record of images from a workshop
Bill Crumbleholme ran at Butser Iron Age Farm in September
The photographs are a series of random shots taken
while constructing the kiln, firing and unloading the pots.
Many thanks to fellow Ancient Wessex Network
member, Mark, for his construction and fire tending. Thanks to Butser for
hosting the event and the good folk from the Chichester District Archaeology
Society for attending the pottery workshop during which these firings took
Initial simple bonfire with pots being dried out. Bill had pinched out and
decorated the shapes the week before and let them dry in the sun, but they
remain slightly damp and chemically combined water needs to be driven out by
The bonfire was first built in the middle, the pots were arranged around the
outside, but not on the downwind side (because sometimes gusts of wind can
sweep flames that way and overheat the pots). Then when burning well, sticks
were placed on it and when they were alight they were moved to around the
outside of the pots to form a burning ring. The fires were then kept stoked
gently to heat up the pots slowly. Care was taken to avoid flames licking
the pots, as that would result in spalling (see below). The pots dried out
and when tapped with a stick they would ring rather than have a dull thud
(as at the start of the firing). They were turned over a few times to even
out the heating.
Meanwhile Mark dug a hole and mixed up the clay-rich soil with water and
straw/hay (one day I'll remember the difference!) which was rolled into fat
coils and used to build up the walls. Turf was used to shore up the sides.
Rolled turves with branches inside were used to form rooves over the two
firebox entrances which had been excavated leading into the main chamber. A
small fire was built in each firebox and the chamber gently heated.
Pieces of broken fired pottery shards were laid out over the base of the
chamber, on which the pots were laid, upsidedown. The shards kept the pots
away from the cold damp base and encouraged the heat to circulate under
them. The bowls that had been pre-heated in the bonfire for a couple of
hours were transfered to the kiln.
The remaining jars were pushed into the middle of the bonfire. More branches
were placed around and top of them and left to blaze.
Sadly the noise of exploding pots started to be heard. It was then apparent
that they had not been sufficiently preheated for long enough at a high
enough temperature to dry them out. The initial drying opens up the pores
and allows steam to escape more easily as they get hotter and the chemically
combined water is released. If the steam cannot escape quickly the pressure
pops the outer skin of the pot off - which is known as spalling.
The bonfire was restoked a couple of times and the temperature built up
until the pots could be seen glowing red in the embers below the fire. After
about 45 minutes of heating the pots were dragged out of the embers to
reveal their state - sadly spalled badly. A plus was that when they were
washed the pots had turned ceramic throughout and did not turn back into mud
The bonfire was raked apart and bits of spalling picked out.
Meanwhile the bowls were being warmed by the occassional flames passing into
the chamber, but they were above the level of the pots, so the pots heated
Unfortunately, before they were dried out enough, a few gusts of wind blew
the flames into the chamber too fiercely and three of the pots spalled.
As time was running out we went for the burn! Branches were lowered into the
chamber from above to form a teepee shaped fire over the pots. They burnt
down to produce a bed of embers which just about covered the pots. The
fireboxes were kept stoked to introduce heated air into the chamber where it
helped the embers produce more heat.
The fire was stoked a couple more times to build up more heat.
Eventually we took the plunge and reached in with the tongs and pulled out
the spalled bowls from their nest of embers.
They were nice and black and took the shock of rapid cooling with water very
well. All completely ceramic.
After a bit longer the rest of the bowls were drawn out and cooled. These
had reoxidised somewhat and turned mottled rather than dark black from the
reduction and smoke. The ash had distressed the surface, but that would
clean off later with a bit of a scrubbing.
The bowls were fashioned in the style of Dorset Black Burnished Ware, with a
foot ring and latticed decoration. Others were inspired by Somerset's
Glastonbury Ware, with more rounded bases and decorated with more a Celtic
style of curved incisions.
A pleasing day's firing! We know where we went wrong with these activities
and learnt some new ideas. Mark's kiln was all the right dimensions and
aperture sizes to get a good heat generation and control.
The small jars were made with clay that did not have very much added to the
mix of "found" clay with some commercially prepared clay - more "inclusions"
would have opened up the body and allowed it to breath as it dried out. They
were also not preheated for long enough and a couple of times they cooled
down a bit rather than steadily got hotter - as the branches burned away and
were not replaced soon enough - trying to save fuel and just being
The bowls were made with more added grog - a variety of ground down fired
pot shards and a mix of reclaimed clays which had all been stored in a
dustbin from previously failed or dried out lumps of clay and mis-fired pot
The blackened pots were blacker than any others ever produced by Bill using
this sort of firing. Leaving the embers to build up without being disturbed
helped them to produce more heat over a longer time. Getting preheated air
flowing into the chamber through the fireboxes by keeping some fire burning
there helped and promoted a more reducing atmosphere in the chamber, which
promotes darkening. Some folk (not Bill!) think the iron oxide in the clay
turns much darker when it is heavily reduced by lack of oxygen. Drawing the
pots hot out of a nest of embers seems the trick. The carbon soot does not
have time to burn away and iron oxide does not reoxidise? Those left for
longer while the chamber cooled a bit had time to reoxidise as the nest of
embers was turning to ash and no longer kept the oxygen out.
Thanks again to everyone involved.
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