of Bronze Age Firing Techniques
There is a great deal of interest in how the Bronze
Age folk (and others) fired their pottery.
Bill has been investigating the possibilities
by trying various methods and gradually learning the pros and cons of
the different approaches.
This document sets out an overview of Bill's methods
of firing, explaining the basic techniques and what he has learnt. Some
of this may be useful to other people wishing to try their luck at ancient
Pit firings are a method of colouring pottery that
has been burnished, used by contemporary ceramicists to create interesting
flashes of colour. This is based on Iron Age technology - although those
folk were hoping for all over blackness. There is a
link to Bill's pit firings here.
Follow this link to an archive page with images and text explaining Bill's experimental firings at Out of Eden in Wales - using an open bonfire and a constructed simple kiln.
Follow this link to see attempts to make Black Burnished Ware, in the Iron Age and Roman styles, using similar technologies to the earlier periods.
this link to see the archive images and explanations of a firing using
a turf construction at Down Farm, Martin Green's farm at Sixpenny Handley.
This is the turf clamp kiln at Down Farm, beginning to warm up a bit!
this link to see details and a video of a firing session making replicas of the
Amesbury Archer Beakers.
Close up view of fired beakers
Description of Firing Experiments.
I used to follow the perceived wisdom that wares
should be dry before firing, but a couple of potters have shown that it
is not necessary if the clay is suitable (maybe a particular type or with
masses of inclusions like grog (crushed fired pots - recycling wasters)).
During a recent firing at Corfe Castle I successfully fired some pieces
made the day before which were still damp, they were heated very slowly
and so dried out before the flames got at them.
My early attempts involved building a small fire and putting the pots
in a ring around it, but the heat rises up in the middle and sucks in
fresh cold air from around the base - so the pots are cooled, not heated
by the passage of air.
I then modified that by having a fire in the middle, putting the pots
round it -
thus being able to position the pots in a ring, the diameter
of which depends on the number of pots. Then a ring of fire was built
around that - see more of the images here
One preferred method is to start with
double line of pots, rather than a ring. The pots are stacked bases outwards
and small pots can be put inside larger ones. With a circular formation
the centre does not get hot enough and any pots put there tend to suffer
spalling (see below). If it is windy the line is at right angles to the
wind, so the heat is carried more evenly towards the wares.
Urns fired in a double row - luckly it rained after they had cooled, so they got a wash.
More images of the firing at the Festival of History at this link
I position the pots on their sides, resting on greenwood twigs or willow
wands. These keep the pots off the damp cold ground and allow air to circulate
under them. These rests must be almost fireproof or at least burn by slow
smouldering, if they burst into flames too soon that will damage the pots.
I build small fires at least a foot away from the pots to start with,
to encircle the pots in a ring of fire (the "ring" may be rectangular).
The fire is kept slowly burning all the way round for 3 or 4 hours, gradually
moving closer in and turning the firewood over so that the radiant heat
from the glowing charcoal hits the pots.
The pots can cope with radiant heat but not direct flames licking over
their surfaces - a flame produces too high a temperature early on. If
the pot still contains water (either dampness or chemically combined water)
and is heated too high too quick, then the water turns to steam and that
sudden expansion blows the pot apart - often "spalling" which
is where the outer surface comes away. Heavy grogged clay is more porous
and allows the steam to escape, some ancient pots were tempered with organic
material - i.e. straw - which forms escape routes for the steam.
The pots turn colour as they get hotter and drier and slightly smoked.
Knowing when they are ready to be taken hotter is tricky. Often a gust
of wind will fan a flame over a pot and it will spall - so you know it
is not ready! On windy days a barrier up wind might be useful to control
the forced air (which could be directed onto the fire when it is at its
After 4 hours or so, the pots should be hot and dry enough for the fire
to be built up. Try moving the fire closer in one corner first and leave
it for a few minutes. If the pots do not spall then move the fire closer
all the way round, turning the wood round to face the glowing parts inwards.
Leave it for a while to let the heat get into the middle of the heap of
pots and to reach the small pots inside. At this stage the twigs under
the pots may start to burn, if possible stamp such fires out with a stick
(but this is a bit risky!)
After say half an hour the main ring of fire can be built up into a wall
- as high as the pots, this is where larger logs are useful to form a
stable structure which will not burn away too quickly. Then cover the
whole area with timber - trying not to rest heavy pieces onto a single
pot, but spreading the weight out and using the wall to support the ends.
English Heritage supplied cut logs some of which were selected as being
like shingles and they formed a fairly tight overlapping roof, which kept
the heat in better. Less authentically a closed boarded pallet or sheet of ply can be used as a temporary roof - which will hold the heat in until it burns away.
Small branches have lots of gaps between them and
so the heat can escape and they burn quicker. Fill in any large gaps that
appear as the fuel burns away.
If enough fuel is available it is best to put a second layer over, when
the first layer has partially burnt and turned to charcoal, that will
be trapped inside and will help raise the temperature. The aim is to get
the pots to glow red - which indicates they have reached about 800 degrees,
the temperature required to turn clay into ceramic.
Let the fire burn down naturally, it will turn to ash fairly quickly and
sink down to reveal the pots. Do not remove the pots from the fire too
soon, as the cooling may crack them. However to avoid patches of smoke
remaining on the pots where they rest in the ash and the carbon does not
burn away, they can be turned over (still in the firepit) - that carbon
should burn away if they are hot enough. Some people prefer the patterns
of carbon smoke on their pots, if so then keep them buried until cool.
I sometimes remove the turf and replace it afterwards for cosmetic reasons,
but I understand from archaeologists that sites were used repeatedly and
tended to form a shallow pit, sometimes several meters across, found by them as a burnt earth lining, often mixed with charcoal. These are very hard to prove to be pottery firing areas, but may have been used for metal working, cooking or charcoal production.
a pit may help protect from wind, which was certainly a favoured method by the iron age, but perhaps moving hurdles would be better - they can also be used as an umbrella if the weather turns damp.
Clamp firing is described on this
That was a lot of work and only worked partially as some of the pots were
underfired and many broke. It was performance art setting it up!
I have done pit firings - using a hole like a large grave - but we were
just smoking already biscuit fired pottery to get interesting patterns
and flashes from oxides and salts. That involved putting the pots in the
bottom of the pit on a bed of sawdust, covering with timber (offcuts from
the local timberyard) up to ground level and then covering with corrugated
iron roof, with gaps at the ends to light it from and let the air in and
smoke out. Light the blue touch paper and stand back as it conflagrates
in a couple of hours.
A large bonfire can be used (Nov.5th is useful!) - put the pots in metal
boxes packed with sawdust and close the lids, bury them in the centre
of the fire before it is set alight. Retrieve the next day. This can work
with raw unfired pots, as the sawdust insulates them from extreme heat
to start with and also the closed box traps the steam and they heat up
in a damp atmosphere, so the steam generated does not have the urge to
escape from the pots in the normal way. As the fire progresses the sawdust
turns to fine charcoal, but may not burn due to the lack of oxygen. If
the main fire is hot enough they will be cooked and turn ceramic.
There are many Health and Safety issues to consider when doing these firings.
I tend to risk only the health of myself and immediate family (my wife
is now chief stoker - as a Guide leader she misses camp fires, but enjoys
fire and smoke!). I exclude everyone else from the firing area, unless
they are sensible adults known to me as unlikely to sue!
I have lost some hair from my arms a couple of times, but with common
sense the risks can be minimised. Buckets of water and crowd barriers
This type of firing undoubtedly helps people to understand the processes
and is very valuable to bring history to life and to show simple technology.
The montage of images below was prepared for a
display, follow the links at each of the hotspots on the images.