FACTORS AFFECTING THE SURVIVAL OF METAL PLOUGHSOIL ASSEMBLAGES: AN ASSESSMENT OF LEAD BULLETS FROM 17TH-CENTURY FIELDS OF CONFLICT

All archaeological buried assemblages are subject to deterioration.Research has focused on the decay of artefacts in stratified contexts from excavations, with less consideration given to the objects from the ploughsoil. In recent years, the acceleration of metal artefact decay has been witnessed, with increases in soil acidification, pollution and the intensification of agricultural practices being identified as key factors in this process. This project examines the various factors which contribute to the decay of metallic archaeological materials in topsoils. The study seeks to identify associations between the decay of materials and their burial environments in order to identify the principal factors influencing deterioration. This will assist in the prediction of site condition and enable the design of mitigation strategies to aid preservation and conservation, highlighting the importance of ploughsoil assemblages as a significant part of our cultural heritage.

This research explores the threats artefacts face in unstratified contexts by designing and applying a condition assessment and mapping the condition of artefacts across landscapes. 17th-century British Civil War sites of conflict, including both battlefields and siege sites,are used as case studies for this research, with lead bullets as the object type examined. Battlefields were chosen for study because they are particularly vulnerable to loss of data as the majority of evidence survives in the form of scatters of lead projectiles and other artefacts in the topsoil.

Three main parameters affect the survival of metal in the ground: soil chemistry and superficial geology, the historic land use of sites, and the chemical composition of artefacts. These factors have been addressed in turn for each case study, in an attempt to identify which parameter has the most impact on the condition and preservation state of lead bullets.

This study has revealed the condition of artefacts can vary greatly in ploughsoil environments. Analysis has shown that a soil’s pH and texture have a significant effect on the preservation of lead bullets. Tin content of the bullets has a slightly negative impact on their preservation. An important discovery has been that probably the most significant aspect of the burial environment is land use history. Bullets were in consistently better condition in permanent pasture fields, overriding the significance of soil chemical attributes, revealing the impact of arable farming has had on the preservation of buried metallic artefacts. It appears the most effective conservation strategy in future would be to retain land under pasture or convert arable land to pasture in order to preserve buried assemblages for the long term.