EXPERIMENTS WITH EARLY MEDIEVAL POTTERY

Arcadia 4-6th October 1997
Peter Beatson NVG Mikligard

INTRODUCTION

In Viking age North-western Europe ceramics were mostly made for local use, with only a few centres (notably in the Rhineland and England) producing high quality wares for export, though in many cases the export was incidental, as containers for trade goods such as wine. As a result there was much regional specificity in the shapes and quality of pottery. As an example, take Scandinavia, and the most common pottery vessel, the cooking pot. In Jutland the standard form was hemispherical, with the rim usually turned inwards (Fig. 1-a), a form existing prior to the Viking period. At the trading ports Hedeby and Ribe, and a few other West Jutish sites globular pots ('kugeltopf') with turned-out rims are found (Fig. 1-b), this is the characteristic 'North Sea' form originating in the Frisian area. Flat bottomed vessels (Fig. 1-c) predominated on the Danish islands, and in Skåne and Sweden proper, probably inspired by the much more accomplished Slav pottery, which was commonly imported into the region until 1200AD. This evolved into a ware of improved quality, the so-called 'Baltic ware' (Fig.1-d). Pottery was rarely used in Norway, where soapstone and iron pots were preferred.

The forms reproduced in the experiments were three Jutland hemispheric pots (like Fig. 2-a), two flat bottomed beakers (East Danish: like Fig. 2-b), and Anglo-Saxon lamps- four pedestal and four hanging lamps (like Fig. 2-c: also known from Lund, Skåne). All pieces were hand-built (ie. without a wheel), as was much pottery throughout the period and region. There is evidence that Danish and English pots were made by coiling (Roesdahl 1982; Vince 1991). The wheel does not appear to have produced a 'pottery revolution', the Slavic wheel products actually differed little in shape from earlier hand made pots (Fig. 3). When the wheel was reintroduced into England during the mid-late Saxon period, it failed to completely displace the hand made pottery industry, in some areas it even disappeared again in the decades before the Norman conquest (Vince 1991). In Saxon London surfaces were smoothed simply by burnishing the leather-hard pots with the palm of a hand, or 'self-slipping'- rubbing over with a wet hand, which causes coarse particles to sink beneath the surface. Glazing was not practised in Scandinavia, though lead-based glazes were used on the highest quality English (Stamford ware) and Rhenish ceramics during the period.

CONSTRUCTION

The terms and techniques mentioned below are fully explained in the technical references. Tempering (addition of grit) helps the clay resist shrinkage and thermal stresses during drying and firing. In the early medieval period local clays were tempered with chaff, crushed shell, sand (often quite coarse) or crushed limestone. Experiments were conducted with terracotta earthenware clay (PS2000: Northcote Pottery P/L 85A Clive St. Thornbury VIC 3071) tempered with 1:10 shell grit [1] (budgie cage stuff), or 1:5 mixed grade river sand (by weight, dry temper added to moist clay). The temper and a little water was added during wedging, about 1.5kg of clay was prepared at a time, sufficent for a modest sized cooking pot. The tempered clay was kneaded before use.

Building was by 'pinching' for smaller forms (lamps). The flat-bottomed beakers were made by coiling, with shape checked using a template, the coils were smoothed into each other by hand. When the beaker had firmed slightly the inturned rim was shaped, then the exterior was smoothed and the rim, shoulder and base edges were defined by light paddling (see below).

Hemispheric pots were built by coiling a rough bowl shape using thick ropes of clay roughly smeared together. The pot was then firmly paddled using a flat wooden spoon over a smooth hard round 'anvil' (in this case a small pot made earlier, but a large stone, or a sock firmly packed with sand will suffice). The pot is supported with the anvil inside, while the exterior is smacked firmly with the paddle, welding the coils into a single mass while stretching and thinning the walls[2]. It is best to work systematically around the pot, paddling from the base towards the rim. Avoid overworking the very bottom or the rim, as this could cause tearing. If the pot becomes 'floppy', its best to leave it (supported inside a soup bowl or something) for half an hour or so to firm up (but do not allow it to dry out, keep out of sun and drafts, wrap in plastic if necessary), before continuing work. The result was thick-lipped and roughly hemispherical. The rim was then paddled gently over a smaller anvil to shrink the opening, finishing by patting it gently down to form the inturned rim, with final shaping by hand. Pieces were aired in a shady airy place for at least one week before firing, with regular turning to avoid uneven drying. The drier the pieces are, the better.

PIT FIRING

Although quite developed kilns have been excavated in some places, most local ware was fired at low temperatures, in a bonfire, pit, or clamp kiln. The firing temperatures have been estimated to be between 600°C (the minimum to transform clay to ceramic) and 850°C, the temperature at which carbonate inclusions (such as shells and limestone) begin to decompose. By contrast, modern ceramics are routinely fired to 1000°C or more. Therefore almost all medieval pottery is 'earthenware', quite porous and not watertight.

A pit was prepared, about 0.8m square and 0.4m deep, cut into the side of a bank that protected it from prevailing winds. A small fire was laid to dry and warm the walls of the pit, as well as to give a final drying to the pots, which were placed about the edge and turned regularly over the course of the morning. The fire was allowed to die out, then a layer of pine bark chips (50 litres, landscaping grade) was placed in the bottom of the pit. The wares were grouped in the centre on top of this layer, with small pieces inside larger ones. Careful and compact placement is required to promote uniform heating and minimise shifting as the fuel burns away, which could crush the ware. More pinebark was used to fill the pots, a layer of kindling were packed them, then pine bark (75-100 litres) was heaped over them until the pit was filled (Fig. 4).

A substantial fire was set over the top of the pit, which was ignited at about 4PM Saturday. The fire was continuously fed with wrist-thick branches for about four hours, producing a hot blaze. Heavy logs should be avoided as they may crush the pots. The surface fire was then allowed to die out naturally. The pine bark burned downwards over the course of the next day and a half, slowly and gently heating the pots[3]. Slow warming is essential as chemically-bound water is driven out of the clay minerals, otherwise the violent escape of steam will cause pots to explode. The wares should reach clear red heat, although this could not be verified as they were still hidden beneath a layer of bark. The bark burned away naturally to the level of the pots, in the final stages it was gradually and carefully cleared away. In any case, don't remove the pots from the pit until well and truly cooled, or they will crack.

RESULTS

The pots were removed on Monday morning. All thirteen pieces survived firing (Fig. 5). When flicked with a fingernail they 'rang', indicating firing had been succesful. Shrinkage of the pieces was about 10% after drying and firing. Their surfaces were mottled reddish and black to various degrees. These colours depend on iron content. Where iron in the clay can react with atmospheric oxygen, it turns the pot surface tan to reddish-orange. In the absence of air, the iron will be chemically reduced, producing a grey to black finish[4]. Mottling indicates that circulation of air within the pit was uneven. In the shell-tempered pieces (the pedestal lamps only, sand was used for all others) the shell did not decompose, indicating that the final temperature reached was relatively low. Two terracotta pots and a white stoneware pot which had already been bisque-fired in an electric kiln (they were made earlier in a pottery class), plus a commercially bought earthenware Lebanese jug were included in the same firing. They also all survived, and showed similar mottling to the other pieces, except the stoneware pot which was made of an iron-free clay, and turned out whitish.

CONCLUSIONS

Ceramics in the medieval style can be produced without the use of expensive materials and equipment (total costs < $50: clay $12; fuel $30; other $5), and the use of replicas should be encouraged to replace the less satisfactory bowls and jugs purchased commercially. Their functionality and durability [5] remains to be assessed, however this should be determined in the next few months of use.

NOTES

  1. Shell grit was not suitable where a lot of stretching of the clay occurs, eg. paddling, and sometimes pinching (eg. flared lamp bowls), as the large shell pieces formed weak spots leading to tearing. Possibly finer crushing would improve it.
  2. It is not known to me whether paddling was a technique used in medieval Europe, although it is widespead among indigenous peoples today. It gives a smooth, almost burnished surface, though the slightly facetted appearance it produces has not been noted by archaeologists.
  3. Apparently globular forms survive pit firing best. The worst are flat plates.
  4. To produce a completely reduced (black) pot is simple. When the initial fire dies down, cover pit with a blanket of finely divided fuel (powdered dung is ideal, perhaps sawdust), then a layer of earth. The excess fuel will quickly consume all available oxygen. The pit is left to cool completely as before, and the pots are dug out. Completely oxidised wares are a little harder to make, penetration of air must be maximised. The pots could be fired above ground, and exposed while cooling (but avoid drafts). Both colorations (and mixtures) were common, it makes little difference to the functionality of the pots.
  5. A natural method of waterproofing earthenware is to fill it with milk, then allow it to sour for about four days. Regular use in cooking will also quickly 'seal' pots, though minimal use of detergents is probably best in this case. Soak pots in water before each use. Never place an empty pot on the fire, adding food or liquid to a hot pot could crack it.

REFERENCES-ARCHAEOLOGICAL

  1. C.J. Becker, L.B. Jørgensen, S. Hvass, L.C. Nielsen, T. Skov and I. Stoumann. Viking age settlements in western and central Jutland: recent excavations. Acta Archaeologica 50, 1979.
  2. T. Ramskou, Viking age cremation graves in Denmark: a survey. Acta Archaeologica 21, 1950.
  3. E. Roesdahl, Viking age Denmark. British Museum Publications: London 1982.
  4. L. Stenholm, Hushållskärl av aldre svartgods. In: A.W. Mårtensson (Ed.) Uppgrävt förflutet för PKbanken i Lund (Archaeologica Lundensia VII). Kulturhistoriska Museet: Lund 1976.
  5. M.W. Thompson, Novgorod the Great: excavations at the medieval city directed by A.V. Artsikhovsky and B.A. Kolchin. Evelyn, Adams and MacKay: London 1967.
  6. A. Vince, Aspects of Saxo-Norman London II: Finds and environmental evidence. London and Middlesex Archaeological Society: London 1991.

REFERENCES-TECHNICAL

  1. L.I. Nigrosh, Low fire: Other ways to work in clay. Davis Publications: Worcester (Massachusets) 1980.
  2. L. Primmer, Pottery made simple. W.H. Allen: London 1974.
  3. H. Reigger, Primitive pottery. Van Nostrand Reinhold Co.: New York 1974.

FIGURES

Figure 1: Cooking pots from Viking age Denmark, (ref. Roesdahl 1982): A. Jutland hemispheric vessel, Arhus; B. East Danish flat bottomed vessel, Trelleborg; C. globular pot, Hedeby; D. 'Baltic ware' vessel, Lund. Scale about 2:7.
Figure 2: Forms reproduced in experiments: A. Jutland hemispheric pot, Trajberg Denmark (ref. Becker et al. 1979), scale 1:4; B. flat bottomed beaker, Bregninge Denmark (ref. Ramskou 1950), scale 2:3; C. pedestal and suspension lamps, London England (ref. Vince 1991), scale 1:4.
Figure 3: Slavic cooking pots from 10th century Novgorod, all wheel thrown except 1, hand made. The flaring shape with pronounced shoulder and upright rim is characteristic of the Ladoga- Novgorod region of Rus'. The wheel was introduced here in the mid-tenth century. The same form was produced until the 13th century (ref. Thompson 1967).
Figure 4: Schematic cross section through the pit, ready to begin firing. Not to scale.
Figure 5: The pots in the pit after firing. The largest vessel is about 24cm diam.
quarfwa@firstnet.com.au