Sampling strategy

The material from each site was assessed following the guidance provided in Bayley et al. (2001) and Paynter (2011). As the slag from all of the sites was in unwashed condition it was cleaned with cold water and toothbrush to remove adhering soil to reveal the full morphology of the pieces for

assessment. The masses of the metallurgical material were then recorded to allow an indication of activity level per phase of occupation to be identified. Prior to any sampling the pieces were photographed to record their original state post-excavation. This was done to mitigate any damage caused during sampling, as slag is a heterogeneous material there is no certainty that a piece will survive sampling comparably intact. This way, even if a piece suffered catastrophic fracture due to heterogeneity a record of the original appearance is preserved allowing for a fuller interpretation of the origin and conditions the piece experienced. The pieces selected for sampling were chosen based upon their morphology, colour and density. These characteristics are the most important in terms of preliminary identification of metallurgical material.

The use of perceived mass – how heavy the piece appears in comparison to its size, referred to as density here for simplicity, as a criterion for sample selection is particularly important in the case of this assemblage where a large proportion of the material originated from smithing processes. In the case of iron slags the density is derived from the quantity of high iron content phases present. It is for this reason that smelting slags which contain significantly more wüstite and metallic iron are

possessed of higher density. This directly impacts upon the colour of the slag as well, with higher wüstite content resulting in a darker slag.

146 By cutting on the diamond saw to obtain analytical samples the damage caused to the slag pieces, whether intact or previously broken, was kept to a minimum. The orientation of the cut was selected based upon how stable the piece was held in the grip of the saw to prevent damage to the saw blade during use. Samples of a thickness not in excess of 1cm were taken so that further analyses could be conducted in future without requiring further sampling of the original material.

Pieces that were not cut using the saw were ground using p220 silicon carbide paper prior to

mounting. This produced a flatter surface on the sample which reduced the time required for grinding and polishing.

The larger pieces were sampled using a hammer and chisel to break a piece off the main body of the artefact. As some of the larger pieces were too large for the saw this was the only means available, which unfortunately does cause more damage to the piece. These samples were ground on p220 paper to flatten the surface prior to mounting to reduce the amount of preparation required before analysis. Each site had its own individual considerations when selecting samples, which are detailed below.

East Yorkshire

All of the material from the sites in the Foulness Valley and Hull Valley is unstratified surface collection finds. The lack of later smelting in the same areas limits the origin of the slag to the Iron Age as a working hypothesis. Representative pieces from each site were selected in order to produce micro-assemblages which could be analysed efficiently.

Caistor

The Caistor assemblage is dominated by smithing slag with a small quantity of unstratified evidence for smelting. These pieces were preferentially selected first in order to include primary production evidence.

Quarrington

The material from Quarrington had previously been examined and so the initial report was taken as guidance for this study. Where stratified material was examined first as this was previously reported in Taylor et al. (2003). The majority of the slag exhibited a flowed appearance with a dark surface which is diagnostic of tap slag. Other pieces which were possessed of high density were placed to one side for consideration as possible furnace slags.

147 The unstratified material was examined as this would provide further evidence of activity on the site as no other ironworking evidence had been recovered from the site except that of Early Saxon date. The two largest pieces of unstratified slag were broken on an anvil using hammer and chisel. This was done to reveal their internal structures to further clarify their nature and origin. One was a smithing hearth bottom, with a light grey interior and the other was a far darker grey synonymous with iron smelting. This characteristic colour combined with the high density lead to the interpretation of this piece being either a small furnace bottom or a large piece of furnace slag. The piece removed from the large smelting slag body was then cut on a rotary diamond saw for analysis.

Within the assemblage there were also two pieces of red stained stone. These may have been ore bearing rock, however the quantity of the red probable ore material remaining made it unlikely that a suitable sample could be taken for analysis without causing significant damage to the pieces. Their presence was recorded and then they were discounted from the pool of desirable analytical material. Flixborough

The quantity of material taken in preliminary selection was limited by my ability to carry the box on public transport. This restricted the size of pieces and overall mass of material I could select, however it did ensure that many of the pieces were of diagnostic nature, rather than non-diagnostic meaning that they were directly suitable for sampling and analysis.

A second selection of material was conducted in order to ensure that material from both periods of iron production were included. This was done in the hope of identifying any changes in phosphorus content in the material over time, which may be indicative of different ore exploitation strategies between periods.