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Lossenham Pottery Project 2024 II - more clays, new kiln

The new kiln was located not far from the priory church site, on the bank above a recently re-excavated pond and looking down to the River Rother. The main innovation in terms of design was the use of two fireboxes ('flues') feeding into a central firing chamber. This type of design was becoming more common in England, particularly in southern and eastern areas, at around the time the priory was built. Aside from the increased combustion area, there may be have been other advantages, such as maintaining a steadier temperature as fires were stoked or raked out, and possibly less effect of wind direction.  As with the first kiln, our design was based on general principles from a number of kilns of the period, rather than specifically trying to recreate one particular example.

 

We used the same building materials as for the first kiln - clay cob (clay soil mixed with sand, hay and water), but took advantage of a little non-medieval mechanical assistance for digging the below ground parts (thanks Nick!).

Digging the base holes of the kiln

 

This time the internal structure was made entirely of cob, building up three flat-topped arches the tops of which formed a flat floor to the firing chamber. The firebox roofs were built over a green willow framework, which was left in place to burn out when the kiln was fired. The chamber itself was more vertical sided than previously (and, we hoped, easier to pack as a consequence), tapering in slightly at the top. The build took place over about a week.

Below-ground parts of the kiln under construction

 

Starting construction of the chamber walls

 

The finished kiln was left to dry, then we experimented with firing (to low temperatures) to get some idea how the airflow worked through the chamber, and help finish the drying process.

 

Packing the kiln this time was more complicated than previously, as many items were glazed, so it was more critical how and where things touched each other. It was also not helped by the range of sizes and shapes of pots we had made - all very well in terms of exploring the diversity of medieval pottery, but tricky to fit together.  We also had various pieces by volunteers who has used Lossenham clay to make their own pots and sculptures and were willing to trust them to the vagaries of wood firing in an untested kiln. The top of the packed kiln was overed with a layer of broken (previously fired) pottery.

Pots - glazed and unglazed - waiting to be packed into the kiln

 

The kiln firing presented some of the same challenges as before, in particular maintaining a steady low temperature for the initial period where the pots are vulnerable to steam fractures - of which we had a few - not helped by the sudden combustion of the willow arches all burning out at the same time. We had a better selection of wood types than previously, which made controlling combustion easier, and the two, and larger, fireboxes were much less prone to getting clogged with ash. Again it became evident that the pyrometer readings were underestimating the temperature in some other parts of the kiln, but we also had potter's cones in strategic locations to provide a second temperature guide. After a little over 14 hours the final cone bent over indicating a temperature of about 1060 °C - the top of what we had hoped to achieve - and the kiln was closed up to cool over the next couple of days.

The kiln firing, at dusk - at a temperature of about 850°C

 

The final cone bending - at about 1060°C 

 

The unpacking produced some very successful pots, some failures, and some problems to puzzle over. Some clays, in some parts of the kiln, had fired very well, with the simple, lead-based, glaze we had used maturing to a good, uncrazed, transparent finish, and the pottery itself having a nice dense earthenware weight and good ring.

In other parts of the kiln - in particular where direct flame contact had been perhaps intense on one side of the pot, had cracked, or in the case of one particular clay, softened to the point of starting to collapse. This clay presented a particular puzzle as test pieces had fired fairly well in the electric kiln. We suspect the problem may be that at least for some of the firing there seems to have been a fairly intense reduction atmosphere in the kiln, and this can alter the way the clay fluxes and vitrifies.

 

We have to remind ourselves that medieval potters still had many 'wasters' - as evidenced by the remains from archaeological investigations of kiln sites - and the benefit of much hard-won experience with their particular kiln and clay. Whilst there is clearly more work to do to understand the best way to pack and fire this kiln, and how different clays perform in it, this first firing certainly demonstrated that it is capable of successfully reaching good earthenware temperatures sufficient to mature both the clays we have on the farm, and simple lead-based glazes not dissimilar to those a medieval potter might have had.

 

We hoped to complete a second firing of the kiln in 2024, but the weather declined and the kiln site became difficult to work in, so the kiln was made secure and weather proof for the winter, with the hope that it might be re-used in subsequent years.

 

Although the focus of the wood-firing was on the medieval pottery (and the pieces contributed by volunteers - which all came through unscathed!), Russell's series of pots exploring the historical aspects of the landscape from other perspectives, including the presence of the Carmelite community, were not trusted to the medieval kiln, but fired separately to produce a memorable series of vessels, and a different testament to the clay beneath our feet.

Russell Burden (2024) - lake bed clay and iron oxide

 

As noted previously, a fuller visual record of the 2024 project, including images of all the pieces from Russell's collection, can be found here.