Dr Melanie Rimmer
Evidence-Based Condition-Monitoring Strategy for Preservation of Heritage Iron (AHRC/EPSRC Science and Heritage Large Research Grant)
Brunel’s ss Great Britain in dry dock in Bristol. Iron forms the fabric of this award-winning museum.
From archaeological iron through to ships, iron is a ubiquitous heritage metal. Iron objects are susceptible to contamination by corrosion-accelerating chloride ions from burial or marine contexts, leading to rapid corrosion during storage and display and the eventual destruction of the object. Desiccation below 15% relative humidity (RH) or de-oxygenation can stop corrosion, but mechanical desiccation is energy-hungry and expensive, while passive use of desiccants to control small spaces is difficult to maintain long-term. There is currently no established understanding of the relationships between chloride content, corrosion rate, RH and object lifespan, leading to considerable uncertainty regarding the most effective strategy for maintaining iron in a world of limited resources.
This research will identify and test new ideas for managing the preservation of iron via the concept of ‘corrosion control’ rather than ‘corrosion prevention’. Experimental work will quantitatively examine long-term corrosion rates of up to 300 samples of archaeological iron and relate to relative humidity, chloride content and physical condition of the samples. These results will underpin subsequent field-testing of heritage iron objects, the development of corrosion sensors and improved management guidelines for the preservation of chloride-contaminated iron.
Investigating the treatment of chloride-infested archaeological iron objects (PhD research)
Archaeological iron objects become infested with chloride ions during burial. Controlling chloride-induced corrosion requires <15% relative humidity (RH); this is difficult to achieve and maintain in practice. This leads to iron objects remaining at significant risk of corrosion when storage mechanisms fail.
This AHRC-funded doctoral award (No. 2007/136517), in collaboration with The British Museum, investigated the effectiveness of chloride removal from archaeological iron using alkaline deoxygenated desalination treatments, and evaluated the benefits and associated risks. A large programme of experimental work was carried out using quantitative techniques to measure chloride extraction, alongside an evaluation of long-term corrosion behaviour, risks from treatment residues and damage to information-carrying corrosion layers during treatment. The data will aid decision-making in the conservation and management of large museum collections of archaeological iron.
The Geoarchaeology of Silbury Hill, Wiltshire: an analysis of buried soil materials and organic preservation (MSc dissertation research)
Silbury Hill, the large Neolithic mound near Avebury in Wiltshire, displays a high degree of preservation of organic remains in the buried soil and central portion of the mound. Excavations at the mound in 2007 by English Heritage provided a unique opportunity to study the soil materials, alteration processes and preservation conditions through a range of analytical techniques. A combination of soil analysis, elemental profiling with portable X-ray fluorescence and thin-section micromorphology was used to study the buried soil and compare it to modern soil profiles in the surrounding area. Alteration processes including the compression of the soil profile and the movement of iron and manganese under the mound were studied and their possible contribution to organic preservation identified. The research was able to answer questions about the origin, alteration and preservation of the buried soil and organic materials under Silbury Hill as part of the wider programme of study of this unique monument.