Firing The Vindolanda Kiln

On May 31st I, with the help of two of the stalwart Vindolanda volunteers, fired the newly built replica Roman pottery kiln at the Vindolanda Museum: See my earlier post Roman Pottery Kiln and Workshops at Vindolanda.

44 pots of varying sizes were packed tightly into the chamber, tile/amphora sherds (actually roughly made curved slabs of fired clay) were then laid over the pack.  On top of this a very coarse mix of mud, gravel and organic material was spread and finally I plastered a mix of sand and clay over the surface, leaving three exit flues at the back of the kiln, through which hot gasses could escape.

I'd made the decision to attempt a black-burnished ware / greyware firing which involves starving the kiln of oxygen towards the end of the firing causing an intensely reducing atmosphere within the chamber.  This has the combined effect of pushing carbon deep into the pores of the clay and converting iron oxide within the clay body from its red Ferric form to black Ferrous oxide.  In the case of this firing this was achieved by closing down some of the exit flues for the last 200 degrees and, once we had reached the target temperature of 900 degrees, completely sealing the top of the kiln then stoking as much fuel as possible into the firebox and then sealing it closed.

The kiln was lit at 8:30am and we began sealing the kiln at 6pm giving a total firing time of nine and a half hours and an average temperature rise of 95 degrees per hour. Once begun, firing is a continuous process, even being distracted for a few moments can result in a temperature drop. As a 21st Century potter I have the advantage of an thermocouple and pyromenter (High temperature thermometer) my Roman predecessors would have had no such technology at their disposal.  Their temperature measuring techniques would have relied on their senses: in the early stages of firing a potter needs to take things very slowly, ensuring that trapped moisture in the clay doesn't blow his/her pots apart, a hand placed over the exit flue will give an indication of temperature and whether the gasses are moist or not; once the kiln is over 600 degrees C the colour of the pots in the chamber, seen through the exit flues will give the potter all the information they need.

I arrived to open the kiln at noon the following day and upon opening one of the exit flues was surprised to smell smoke, and by the level of heat emanating from the kiln. I realised that the fuel in the firebox had converted to charcoal and that, with the influx of oxygen caused by opening the seal, it was about to reignite.  We therefore opened the firebox and immediately raked out all the accessible fuel which did indeed immediately burst into flame. We then resealed the kiln because the pots were obviously too hot to unpack, unfortunately not having anticipated this turn of events, I had not brought the pyrometer with me and there fore while I knew it was hot, I didn't know how hot!  If fired pots are cooled through the 250 to 200 degrees stage too quickly they can crack, known as "dunting", this is caused by the fact that silica molecules within the clay rearrange themselves at 226 degrees, so it's safest to wait till the kiln is below 200 degrees to open it. After a trip to my workshop to collect the pyrometer, we returned to the kiln at 4pm by which time the temperature was 186 degrees  and the decision was taken to open it.

I think the results speak for themselves, everything was well coloured by the reduction, the variations from pale grey to black being very much in keeping with Roman originals.  If you'd like to own one of the pots from this firing watch the Vindolanda website and my Blog for news, or drop me an email and I'll let you know when they come up for sale.

Visit my website at www.pottedhistory.co.uk

Roman Pottery Kiln and Workshops at Vindolanda

I'm really excited about this new collaboration with Vindolanda Roman Fort near to Hadrians Wall, the first stage has been to create a reconstruction of a Roman pottery kiln as a permanent feature of the site. Built with the help of a very enthusiastic team of Vindolanda volunteers, the kiln is sited in the valley, beside the burn, near to the museum and visitor centre, so look out for it next time you're there.

This fully functional replica of a Roman up-draft pottery kiln, is based on information gained from the excavation of such kilns at archaeological sites across the North of England. The body of the kiln itself (1) is constructed entirely from a mixture of materials found on site, Clay, Earth and plant matter such as straw. The internal floor and central support, (2) also known as Kiln Furniture are made from specially selected clay which will survive repeated exposure to high temperatures.

While the kiln is cold, dry, raw pots are packed into the Ware Chamber (3) the top of the kiln is closed off with a temporary dome of clay and straw (4), leaving small holes as exit flues. A small fire is then lit in the Fire Box (5) allowing hot gasses and flames to pass through into the combustion chamber (6) then up through the ware chamber. Starting slowly and steadily building up the fire the the pots are brought up to a temperature of between 8000 and 10000 Centigrade.

The first firing took many hours of constant stoking as we not only needed to fire the pots, but to dry out the structure of the kiln itself. Nevertheless we achieved a temperature of between 700 & 800 degrees Centigrade, hot enough to fire the kiln load which included two amphorae.

This type of kiln would have been used by potters working in this region, to manufacture coarse wares such as Black Burnished Ware and Gray Ware cooking pots, indented bakers, plates, bowls, flagons and the like. While fine wares such as Samian Ware, Terra Sigillata and the Aphorae that carried produce around the empire would have been imported from production sites in Gaul and elsewhere in the Roman World.

The latest firing of this kiln is recorded here Firing the Vindolanda Kiln

From now on I will be running regular Roman pottery workshops at Vindolanda where you will be able to learn the techniques and skills that went into making the ceramics of the Roman Empire. Workshops and courses will include: Kiln Building & Firing; Samian Ware; Barbotine Ware; Black Burnished Ware; Lamps & Goddesses; The Potters' Wheel, Roman Head Pots. For more information on these workshops, follow me on Twitter @PottedHistory, visit the Vindolanda website or email me info@pottedhistory.co.uk.

Visit my website at www.pottedhistory.co.uk

Greek Pots for Dr Michael Scott

Having made the replicas used by Dr Michael Scott in his brilliant BBC2 TV series; "Who Were the Greeks", see my blog entry "TV Props, Greek Bronzes Made From Clay" , I was delighted when Dr Scott contacted me and commissioned some replicas to use in his teaching at Warwick University. Now I will say at this point, when Michael contacted me I had anticipated that I'd be making some fairly high status pieces but I wasn't quite prepared for the reference material that he eventually sent me. On a trip to the British Museum he'd taken some photographs of some of the most magnificent Greek pots that he could find: the Douris Cooler, the Berlin Krater, the Phrynos Kylix and the Sharpedon Kylix:

I've replicated Greek red and black figure pottery before but these pieces were the creme de la creme, they were high status when they were first created and they're still high status today. why? Well for the complexity of their manufacture, the refinement of their form and by no means least, the skill of the painter who decorated them. The pots shown here are my, or should I say our replicas not the originals. I made the pots, but my wife Lynda Taylor, a professional artist, decorated them, they required the best! 

The precision with which the pots are made, the perfect alignment of the stem of the kylix and the crispness of the foot, shoulder and rim of the krater, tell me not only that they were made by a highly skilled potter, but that the potters' wheel on which they were thrown was very stable indeed. This was no rough stone disk pivoted on a point of rock, it was a precise piece of machinery with smooth running bearings. The same is true of all of these pots and while the potters making cups and bowls for everyday use may well have made use of primitive wheels these craftsmen had access to the very best tools. They have used that technology to push the making process to new heights, creating forms that say "Look what I can do".

More to come later, watch this space.

Visit my website at www.pottedhistory.co.uk

Roman Pottery Kiln Progress

Installed the Ware chamber floor today and started applying the clay lining.  Unfortunately there won't be any further work on it until Monday at least.

Visit my website at www.pottedhistory.co.uk

Roman Sunken Kiln Under Construction

I can't believe that it has been so long since I've recorded my work here, it's been a very busy summer so there's lots of catching up to do, but I'll get to that over the winter.

 

Over the past couple of days I've been building a sunken type Roman kiln for my own use not far from my workshop.  The site was kindly offered by retired potter (I'm not sure that such a thing exists) Alastair Hardie & his wife Kate at Westfield Farm, Thropton Northumberland.  It is situated at the rear of the farm on a raised sand bank about two meters above the flood plain of the Wreigh Burn.  The ground consisted of about 50cm of compacted soil and building rubble, the residue of the concrete floor of an agricultural building which once stood on the site, over natural compacted sand.  This has proved to be an ideal situation, the compacted surface gives strength to the structure while the sand is relatively easy to work and provides a very well drained base for the kiln.

Although I was working alone, the digging of the ware chamber, stoking pit and fire box and the lining of the latter with ceramic brick took less than eight hours.  For the sake of speed I have used some recycled fire brick in the lining of the firebox.  This is the area of the kiln that most archaeologists would refer to as a flue, this is an incorrect use of the term, as the function of a flue is only to carry gasses from one part of a kiln or furnace to another, as in 'exit flue' which as the name suggests carries waste gasses out of the kiln.  The firebox by contrast is where the fuel is burned.  

Today I'll be setting the floor, again for the sake of speed, using modern refractory but I may replace this later for experimental purposes.  I'll report back later today.

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Ancient Firing Technology

Most books one reads talk about 'bonfire firing'; fast open firings using large quantities of wood and accepting a quite high percentage of loss. But it's my belief that large open outdoor fires would have been used only for very large pots and even then the fire would have been very carefully controlled. People in subsistence economies do not waste fuel resources or their own labour. Most beakers would have been made in the house while sitting around the fire, they would then have been placed on the perimeter of the hearth and left there for several days, turning them occasionally, until they were absolutely dry. The pot would then be moved closer to the fire to begin preheating. Fine pots like beakers require a relatively slow firing and the best way to start is to invert the pot with its rim on three small stones over a small amount of hot charcoal, replenishing this until the pot reached about 400C; with most natural clays this will be indicated by a visible darkening of the body. At this stage hot charcoal can be built up around the pot and after a further few minutes small kindling added and the pot fired up to red heat, best seen in the darkness of a hut interior.

Come along to one of my workshops and help make the magic happen.


Visit my website at www.pottedhistory.co.uk

TRIAL BY FIRE

With any ceramic piece the firing is always the most risky part of the making process but this is particularly the case with prehistoric, open fired pots.  This weekend has seen me firing a Neolithic bowl, beakers, food vessels, canopic jars and a 17th Century slipware wedding plate although this last item I have to confess is in the electric kiln.  It's needed for a wedding in a week's time and there's no margin for error

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Samian at Last

I have finally managed to find the time to fire the batch of Samian Ware that I made over a month ago! Much to the relief of some of my customers!

Visit my website at www.pottedhistory.co.uk

Mediaeval Pottery Kiln at Shotton

A few days ago I was invited to visit the archaeological excavation of a pottery production site at Shotton, to the north of Newcastle upon Tyne. This site is sceduled for surface coal extraction by Banks Development and has been excaveted in advance of this by Tyne and Wear Museums. What they have found is a small medieval settlement with evidence of pottery production including a kiln and clay extraction pits. The whole site is on solid clay a fact that has made the conditions in the trenches less than pleasant. As you can see in this photograph of the kiln mud and ice were the order of the day but they were kind enough to remove the ice and pump out the water so that I could inspect it. These conditions suggest that some of the post holes around the kiln must surely have been supports for a roof, otherwise the kiln would have been inoperable during most of the year.

I have taken clay samples from the site with the intention of firing them under an assortment of different firing conditions so that they can be compared with the potsherds from the excavation.