Fire-cracked stones and ceramic production  

The second part of my paper will hopefully throw new light on a previously long established assumption that Bronze Age Trevisker-ware pottery was made of gabbroic clay from the Lizard peninsular.   Michael Parker-Pearson in his paper for Cornish archaeology (1990: 5-32) says: 


'The Cornish Trevisker series, originating from the gabbroic Collard urns and Food vessels, was predominately made of gabbroic clay, also the restricted location of gabbro and serpentine to the Lizard peninsular... and ... the large rock inclusions in many of the vessels made such identifications relatively simple.' 

There is no doubt that gabbroic inclusions are found in the Trevisker series vessels; it is how they came to be inclusions that is the basis of my research for this paper. The Lizard peninsular is 60 kilometres overland from the Trevisker area on the north coast of Cornwall. There would have been no road systems at this time and the topography would have been difficult to traverse with many densely wooded valleys and hills. The alternative route could have been by sea around the Land's End peninsular and up the north coast, a distance of approx. 160 kilometres. Ceramic manufacture throughout the ages is usually found at the source of the raw material. Transporting wet clay for pottery manufacture is not a task endured unless absolutely essential.  


Colin Renfrew (1977: 71-90) suggested that the ceramics were made at the clay source. He says: 'whether they were produced by specialised potters living on the clay source or by potters coming seasonally from different settlements in the Cornish peninsular is not known. The high ratios of gabbroic pottery in settlements assemblages many miles away in north Cornwall indicates that substantial quantities were moved long distances.'  


In order to find these gabbroic ceramic manufacturing sites The Lizard Project landscape survey was undertaken between 1978 and 1983 by members of the local archaeological society. Contrary to expectations, instead of finding large quantities of gabbroic pottery, ceramic manufacturing centres, or the remains of wasters from kilns, no production sites were found from this extensive survey and very little gabbroic pottery shards also. Smith (1987:13-68), who wrote the report, said that 'despite the fact that the original aim of the project was to locate the source of gabbroic pottery production, the survey produced only small quantities of such pottery'.  


Consequently it was suggested that perhaps the plastic quality of the gabbroic clay was so good that small quantities of the clay could have been transported to other areas where it could be mixed with local, less plastic clays, to produce a clay adequate for ceramic production. ApSimon and Greenfield (1972: 355-6) suggested that additional minerals found in Trevisker ceramics were evidence of local inclusions from the Trevisker area with the gabbroic clay, which they suggest was collected in periodic and seasonal visits to the Lizard peninsular.  

It is also suggested by Blackmore and Peacock. 'the transport of raw clay over many miles is documented ethnographically and it is not impossible that inhabitants of settlements such as Trevisker and Gwithian might travel the 30 to 50 km by land, or even sail around Land's End, to collect raw clay'.

All these suppositions are feasible only if the local clays in the Trevisker area were unsuitable on their own to manufacture ceramics. During the last few months I have conducted an extensive survey of local clay sources in the Trevisker area with astounding results. I consulted local farmers in this survey in order to find these clay sources. The farmers that I spoke to were amazed that I thought I might have difficulty in finding clay in their area as they have so much clay it has hampered their farming practices quite considerably. They informed me that the entire landscape is so clay rich that for generations their families had added tons of sand and lime to try to break it up in order to grow crops. This has had little affect and the farmers must content themselves with stock farming only. The clay that I found in the stream banks in this area is of astonishingly high plasticity; it is not only possible to roll and bend this clay with ones fingers straight from the stream bank, but to be able to make a spring coil. This clay is also totally free of inclusions. Finding this highly plastic ceramic-quality clay in the Trevisker area makes it inconceivable that Bronze Age settlers would want the gabbroic clay mixed with this clay (as it is of higher quality than the gabbroic).


Ap Simon and Greenfield's (1972:355-6) analysis of the Trevisker wares show that there were local clays in it from the Trevisker area. So how is it that the large, easily identifiable gabbroic particles came to be found in the ceramics? I believe I have a possible solution to this question. Over the years, I have acquired an expertise in the use of igneous stones in cooking practices in prehistoric times. The use of firestones for cooking in hunting camps is known as fulata fiad in Ireland, and is well documented and identified in the archaeology as piles of fire-cracked stones or burnt mounds. A survey of the longevity of stones used in this practice was conducted by Victor Buckley (1990: 170-172), who says: 'Whereas many types of stones can be used for this purpose it was found that gabbroic stones were by far the best and can be used more than 25 times before they begin to crack'. The use of cooking and heating water with hot stones would have been an important part of daily life in prehistory. Fires were always alight in pits in dwellings, and stones in the fires required no more wood to keep hot, yet when plunged into water they heat water quicker than the electric kettles we use today. However these stones do eventually crack and break and become too small to use and are discarded. I have found during my researches of smelting that these stones, crushed and added as a filler or 'grog' to clay, make excellent crucibles to be used in the smelting process.


It occurred to me that a solution to the gabbroic clay Trevisker-ware anomaly could have its source in the cooking practices used during this period. Let's look at the broader picture. In the Trevisker area the soil is so clay rich that it is almost impossible today to grow crops in it. So how did the many settlements in this area acquire the grain found at excavated sites? As they had the clay, it is conceivable that they used this bountiful resource to produce ceramics to trade for their grain. Trevisker pottery is found at sites all around the coastal area from the Lizard peninsular, Land's End, and up the north coast to Trevisker. It is possible that trading ships started from the Falmouth area and picked up ballast for their boats in the form of gabbroic stones (for cooking), as a secondary trading commodity. As they travelled around the coast they could have picked up grain to trade with the ceramic producers of Trevisker. The gabbroic firestone ballast (an extra trading commodity for the grain) would then be offloaded. There would be no need for ballast on the return journey because of the weight of the finished ceramics.


After the stones had become too small to use, they could have been crushed and added as a 'filler' to the fine plastic clay of the area, and the pots would then appear to have been made of gabbroic clay because of the large particles of gabbroic stone found as inclusions. (There are fine grains as well as larger particles when crushed.)

When gabbroic clay is wet sieved, there are 25% inclusions in it, but half of these inclusions are fine grained. When crushing a gabbroic stone lightly the same proportion of fine grains are produced.


To test this hypothesis it was necessary to manufacture one of the large Trevisker vessels, using the Trevisker clay and crushed gabbroic firestones. However in the Cornish archaeology there has yet to be discovered any evidence of ceramic firing techniques from the Bronze Age, therefore after manufacturing my replica funerary urn, I decided to fire it in the simplest way possible, which was also a way that would leave no traces in the archaeology. I laid the urn on its side on a flat area in the middle of a grassy field. I had thought carefully about the type of fuel to use and felt that dried Blackthorn (Prunus spinosa) would be ideal for this purpose. This hardwood shrub is very prolific in Cornwall in general and the pollen is found in Bronze Age levels in the county. I chose a windless day for this firing and lit a small fire of the dried Blackthorn just to the side of the urn. As the fire intensified, I gradually covered the urn with the blackthorn sticks until it was engulfed completely in the flames. I intended to continue to feed the fire for at least two or three hours, but after one hour exactly, a stick fell onto the urn and the resounding ring indicated that the pot was, indeed, already ceramic. So I stopped feeding the fire and left it to burn itself out. When I examined the urn later I found it to be perfectly fired, displaying on the side that had been lying on the grass a large black scorch mark, exactly mirroring the ones exhibited in the local museum. It is astonishing that the firing of such a large vessel should be so very easy and use so little fuel in the process.  I have found over the years of conducting experiments in many fields of experimental archaeology that this is usually the case.  We tend to visualize in our minds that all these processes must be very complicated, yet in practice I have found that it is just the opposite.  It is experimental archaeology that is now pushing open new doors in our understanding of just how efficient , yet simple, the daily chores of prehistory were.