Shining a light on marine archaeological iron: understanding the kinetics and mechanisms of degradation to inform future conservation strategies

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The conservation of large scale heritage structures, such as buildings and ships present particular challenges for conservation scientists. The scale and complexity of materials, their unique histories, and the difficulties of studying the systems means that the underlying mechanisms of ongoing degradation are poorly understood - which in turn results in non-optimum conservation choices. The conservation of archaeological iron from marine environments is complicated by the ingress of Cl ions whilst in the burial environment from seawater. Despite extensive washing, residual Cl typically remains bound in these structures and this can rapidly react with iron on drying to form expansive corrosion products - potentially completely destroying precious items of cultural heritage. This project will focus on archaeological iron from the Mary Rose: Henry VIII's Flagship. Previous X-ray analysis, investigations of a set of iron cannonballs, which have been subjected to different conservation treatments, has informed us on the efficacy of previous treatments, both retrospectively and in real-time experiments, in terms of corrosion products formed. The next step is to develop an understanding of the reaction pathways to the products formed and to investigate the kinetics of these mechanisms as a function of the various conservation parameters (e.g. such as soaking solution, temperature and relative humidity). In addition to individual objects (such as cannonballs), we will investigate how iron deposits in wood behave, with the overarching aim to find viable solutions for conserving notoriously difficult composite artefacts, defined as a mixture of both organic and inorganic materials e.g. an iron fixture in a wooden artefact. To achieve this in-situ cells will be developed so that the corrosion can be monitored in real-time using spectroscopic and scattering techniques. The results will inform future conservation strategies not only for the Mary Rose project, but other heritage project conserving both marine archaeological iron and composite objects