Saving heritage ironwork from the ravages of rust
Studying effective corrosion cures to help our museums preserve ironwork for posterity.
Most museums in Britain house collections of archaeological and heritage iron objects that are rapidly rusting away due to an absence of evidence-based management strategies for their display and storage.
Without intervention, iconic attractions such as ss Great Britain in Bristol will be significantly damaged by corrosion in a matter of decades. In 1999 a report identified that ongoing corrosion of the ship meant that its estimated life span was 25 years.
By determining the effect of low relative humidity storage on the corrosion rates of iron and chloride bearing corrosion products, our experts identified that desiccation was the most predictable way to control corrosion of the chloride infested hull. Quantifying and scaling the effectiveness of desiccation as a treatment delivered a management tool for preserving the hull.
First, it informed the engineers and architects designing the humidity control system as to how dry the environment around the hull must be to prevent corrosion.
Second, it offered a choice to those managing the survival of the ship; either prevent corrosion by generating a very low humidity in return for high financial and energy outlay or accept a degree of corrosion by maintaining a higher humidity but with lower running costs.
The cost benefit decision is to maintain a controlled relative humidity of 20% within the space around the ship. While this does not prevent corrosion entirely, it is reduced to a negligible rate to vastly extend the life of the ship.
ss Great Britain
Isambard Kingdom Brunel's ss Great Britain is a museum ship and former passenger steamship, with advanced design features that heralded modern ship design. She was the first ocean-going, iron-hulled ship and the longest passenger ship in the world from 1845 to 1854.
Outputs from the research have established storage guidelines for archaeological and heritage iron that have been adopted by English Heritage, the British Museum and the Museum of London, amongst other institutions.
This research into low humidity corrosion ensured the survival of the ss Great Britain, allowing it to produce considerable social and economic benefits for the city of Bristol where it is its number one visitor attraction. Additionally, it introduced and established evidence-based management protocols capable of providing cost benefit analyses for ongoing preservation of chloride contaminated heritage iron.