The applicability of subcritical fluids to the conservation of actively corroding iron artifacts of cultural significance

Since 2003, over 150 experiments using subcritical fluids for the stabilization of metallic cultural heritage have been carried out using 2 reactors at the Warren Lasch Conservation Center (WLCC) in Charleston, South Carolina. The results of the testing have been particularly encouraging for samples and artifacts made of iron and its alloys. The most recent work has entailed desalination of multiple artifacts within one batch, such as wrought iron ballast blocks from the submarine H.L. Hunley (1864), and miscellaneous artifacts of varying composition, context and state of preservation from the National Park Service (NPS) collection. It is suggested, that subcritical conditions significantly enhance the characteristics of a desalination solution through the decrease of viscosity, density and surface tension, thus resulting in improved diffusion constants of the anionic exchange of chloride and hydroxide ions. In addition, long-term stability appears to be enhanced by transformation of corrosion products into more stable forms.