Introduction

In April 2007 a small group of volunteer (and mainly first-time) potters, led by archaeologist Stephen Harrison and professional potter Andrew Appleby, began a three-year experimental research project into the making of Neolithic pottery (for background, see Reference HodgeHodge 2007: 47-51). The project, based at Fursbreck Pottery, Harray, Orkney, aims to come to some potential understanding of the processes involved in the manufacture and firing of prehistoric ceramics and their use during the third and early second millennia BC within a specifically Orcadian context. This broad aim subsumes a number of key objectives: to replicate a range of Neolithic ceramic styles experimentally; to explore the techniques needed for the manufacture of these types of pottery; to come to some assessment of the working properties of locally-derived raw materials; to study the effects of adding tempering agents to the raw materials used; to undertake a range of firing experiments; to experiment with the use of vessels; to assess weathering on vessels and sherds placed in a range of different environmental settings; and to create a body of experience that will be of use in the interpretation of Neolithic pottery from the regional archaeological record. All aspects of the experiment are being recorded in a range of media: detailed written notes, audio recordings, still photography and film.

The purpose of this short paper is to report on the first experimental firing, held at Fursbreck Pottery in August 2007.

The pottery

Figure 1.

A selection of Grooved Ware vessels (photograph: Stephen Harrison).

One hundred handmade vessels of the Later Neolithic Orcadian Grooved Ware type were made using two very different locally derived clays; first from the aptly named Clay Loan in Kirkwall and second from a coastal deposit at Stackle Brae on the island of Eday. The clays, kept separate, were soaked and then the larger rock inclusions (15-20mm >) were removed by hand. Vessels were tempered with chopped organic material, with added small rock inclusions, mostly sedimentary sandstones but with occasional metamorphic pieces, or with beach sand; some examples received no temper other than that which remained in the raw material after initial sorting. Pots were made using a coil and pinch technique, and constructed in a range of sizes: small cups, through small and medium sized tubs, to a small number of very large vessels (broadly, between c. 2000 and 35 000cc). Decoration, based on the archaeologically recognised repertoire of locally used motifs, was applied and/or impressed. Most vessels were finished by the addition of an applied slipped surface and, once leather hard, by burnishing. Others were left coarse.

The kiln

How to fire the pottery — surface bonfire, pit or kiln — proved something of a dilemma. No Neolithic pottery kiln has so far been unequivocally recognised in the British archaeological record. However, a Neolithic structure found at the Knowes of Trotty, Harray, in 2006 has been interpreted by its excavators as a probable pottery kiln (Card et al. 2006: 24-5). A literature search by this author also revealed two possible kiln sites of similar age at Allt Chrisal, on the Outer Hebridean island of Barra, excavated in the 1980s (Branigan & Foster 1995: 85-8). All these features appear to have had turf superstructures. Using the very limited evidence from these sites, a circular, turf-walled kiln was built. This structure, constructed on a level surface cleared of c. 0.2m of topsoil, was 1m in internal diameter at the base and 1m in height, with walls c. 0.6m wide at the base tapering to 0.3m at the top. The upper layers of turf were slightly corbelled, giving the firing chamber an internal diameter of c. 0.8m at the top. Hollow ceramic tubes were built into the turf wall at two locations around the circuit, one 0.18m and the other 0.5m above the base of the firing chamber, to allow for the insertion of thermocouples during firing. The turves, cut in square and rectangular blocks (c. 0.3 x 0.3m and 0.6m x 0.3m) to an approximate standard thickness of 0.15m, were dug from a loamy soil, and loosely laid in a version of English bond. Approximately 20m² of turf was used to construct the kiln. Rough flagstone blocks were occasionally added to the wall circuit to give added strength and stability and to level up individual layers of turf. In terms of labour investment, one person took three-and-a-half hours to cut the turf, whilst two people took four hours to build the kiln.

Figure 2.

The kiln (photograph: Stephen Harrison).

The firing

At 0845 on Saturday 25 August 2007 a wood fire was started on the base of the firing chamber. Within 30 minutes this had reached a maximum temperature of 835°C; thereafter, it was allowed to die down. The glowing embers were then spread evenly across the floor of the kiln and covered with a layer of crumbly peat. Three tiers of vessels were introduced next, each separated by a layer of peat mixed with chicken manure and dried cattle dung. A peat dome was then constructed, standing c. 0.4m above the top of the kiln. Finally, the dome was sealed with a thick layer of damp seaweed. In total, c. 450kg of fuel was used.

Two thermocouples were used to monitor temperatures at regular intervals. Firing was long and slow: altogether, some 40 hours passed between loading the kiln and removing the last vessels. Fifteen hours after firing began the lower thermocouple recorded a temperature of 322°C, the upper 406°C. Thereafter a steady rise took place, until at 0930 on the Sunday morning a maximum temperature of 1031°C was obtained. It was only in the latter stages that the peat actively ignited and burned; prior to this it smouldered.

Figure 3.

Glowing embers from the preheating wood fire (photograph: Stephen Harrison).

Figure 4.

Loading vessels (photograph: Stephen Harrison).

Figure 5.

The loaded and firing kiln (photograph: Stephen Harrison).

No uniform temperature was recorded across the fuel mass at any time during the firing. Instead, the fuel was characterised by intensely hot through cool to cold pockets. In other words, the heat migrated around the kiln, with hotspots here and there, which then cooled down as the heat transferred to adjacent areas. Another interesting dynamic was that the heat worked around the outer edges of the fuel from the base upwards, with the central mass being the last to burn.

Figure 6.

The fired kiln in process of unloading (photograph: Stephen Harrison).

Results

The firing was successful, and a range of very passable Grooved Ware vessels produced. The survival rate of the pottery was high, with 70% of vessels remaining intact; overall, pots with the most coarsely tempered fabric (sandstones with occasional metamorphic pieces) survived the best, presumably because of the bulk of the inclusions rather than any particular efficacy on the part of this type of inclusion. Interestingly, those vessels manufactured from the Stackle Brae clay were the ones that consistently failed, a result of the high sand content found in the clay in its natural state. When additional temper in the form of organic material was added to this clay, pots survived well.

Conclusions

As a result of the outcome of this firing, further experimental work is planned to assess the minimum quantities of a variety of inclusions that can be successfully fired by this method, and to compare these with archaeologically attested Neolithic fabrics. A survey of local clay resources is also ongoing with a view to isolating more precisely the origins of those ceramic fabrics found across the archipelago, and this collection of clays is being integrated with the experimental firing work.