The iron bars from the ‘Gresham Ship’: employing multivariate statistics to further slag inclusion analysis of ferrous objects.

An assemblage of post-medieval iron bars was found with the Princes Channel wreck, salvaged from the Thames Estuary in 2003. They were recorded and studied, with a focus on metallography and slag inclusion analysis. The investigation provided an opportunity to explore the use of multivariate statistical techniques to analyse slag inclusion data. Cluster analysis supplemented by principal components analysis revealed two groups of iron, probably originating from different smelting systems, which were compared to those observed macroscopically and through metallography. The analyses reveal that the bars were formed from raw blooms, and all were made with iron produced by the direct process. The outward uniformity of the bars is at odds with the variable quality of iron displayed within and between bars.