Eleanor J. Schofield

Strain development in nanoporous metallic foils formed by dealloying

Nanoporous Au foils were formed by dealloying a Ag–Au alloy in concentrated HNO3. The resultant foils, which have a “spongelike” morphology with interconnecting ligaments, were studied using synchrotron-based diffraction. A three-dimensional visualization of the nanostructure is generated from small angle experiments and the lattice parameter is derived from diffraction. The data show the development of two interspersed nanoscale strained regions within the material: one in significant tension and one in compression. We interpret this by considering regions of high positive and negative curvatures in the material; this curvature decreases with increasing pore size resulting in a relaxation in lattice strain.

Nanoparticle De-Acidification of the Mary Rose

The preservation of waterlogged archaeological wooden finds, such as Henry VIIIs flagship the Mary Rose 1 , 2 , 3 , is complicated by the biological, chemical, and mechanical changes induced from prolonged exposure to a marine environment. Of particular concern are sulfur species that form acidic compounds that attack wood 4 . Here we show that different sulfur compounds do not form acids at the same rate or pathway and propose a preservation strategy of applying SrCO3 nanoparticles. These nanoparticles not only neutralize problematic sulfuric acid, but also reduced sulfur compounds, such as sulfur and pyrite, which pose a long term threat. This is the first treatment that eliminates acidification at the root. Although this strategy was devised for the Mary Rose, it could be employed to preserve any archaeological organic artifact rich in problematic sulfur, from sunken ships 5 , 6 and silk tapestries 7 to ancient texts 8 and parchments 9 .

XAS studies of the effectiveness of iron chelating treatments of Mary Rose timbers

The oxidation of sulfur in marine archaeological timbers under museum storage conditions is a recently identified problem, particularly for major artefacts such as historic ships excavated from the seabed. Recent work on the Vasa has stressed the role of iron in catalysing the oxidative degradation of the wood cellulose and the polyethylene glycols used to restore mechanical integrity to the timbers. In developing new treatment protocols for the long term preservation of Henry VIII of Englands flagship, the Mary Rose, we are investigating the potential of chelating agents to neutralise and remove the iron products from the ships timbers. We have explored the use of aqueous solutions of chelating agents of calcium phytate, ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA) and ammonium citrate to extract the iron compounds. All of these solutions exhibit some level of iron removal; however the key is to find the most effective concentration at pH of around 7 of the reagent solution, to minimise the treatment time and find the most cost-effective treatment for the whole of the Mary Rose hull. Fe K-edge XAFS data from samples of Mary Rose timbers, before and after treatment by the chelating agents mentioned has been collected. The data collected provide valuable insights into the effectiveness of the treatment solutions.

Application of Microfocus X-Ray Beams from Synchrotrons in Heritage Conservation

Synchrotron-based techniques are becoming increasingly important in heritage science and the aim of this article is to describe how recently developed microfocus methods can probe the elemental composition, speciation and structure at the micron level in samples from structures. Firstly an outline is given of the major techniques that are used, namely x-ray fluorescence, diffraction and absorption spectroscopy, and the information that they can provide. This is followed by a description of the experimental set-up and procedures. The application of the methods is exemplified by case studies of the degradation of three types of historic structural materials; marble, glass and ship timbers. The results of the studies and their role in developing conservation strategies are described.

The Effects of Mary Rose Conservation Treatment on Iron Oxidation Processes and Microbial Communities Contributing to Acid Production in Marine Archaeological Timbers

The Tudor warship the Mary Rose has reached an important transition point in her conservation. The 19 year long process of spraying with polyethylene glycol (PEG) has been completed (April 29th 2013) and the hull is air drying under tightly controlled conditions. Acidophilic bacteria capable of oxidising iron and sulfur have been previously identified and enriched from unpreserved timbers of the Mary Rose, demonstrating that biological pathways of iron and sulfur oxidization existed potentially in this wood, before preservation with PEG. This study was designed to establish if the recycled PEG spray system was a reservoir of microorganisms capable of iron and sulfur oxidization during preservation of the Mary Rose. Microbial enrichments derived from PEG impregnated biofilm collected from underneath the Mary Rose hull, were examined to better understand the processes of cycling of iron. X-ray absorption spectroscopy was utilised to demonstrate the biological contribution to production of sulfuric acid in the wood. Using molecular microbiological techniques to examine these enrichment cultures, PEG was found to mediate a shift in the microbial community from a co-culture of Stenotrophomonas and Brevunidimonas sp, to a co-culture of Stenotrophomonas and the iron oxidising Alicyclobacillus sp. Evidence is presented that PEG is not an inert substance in relation to the redox cycling of iron. This is the first demonstration that solutions of PEG used in the conservation of the Mary Rose are promoting the oxidation of ferrous iron in acidic solutions, in which spontaneous abiotic oxidation does not occur in water. Critically, these results suggest PEG mediated redox cycling of iron between valence states in solutions of 75% PEG 200 and 50% PEG 2000 (v/v) at pH 3.0, with serious implications for the future use of PEG as a conservation material of iron rich wooden archaeological artefacts.

Illuminating the past: X-ray analysis of our cultural heritage

To protect our cultural heritage, it is essential that we understand the material properties of artefacts. Detailed information can be obtained on complex and often highly degraded materials using synchrotron X-ray analysis, aiding our ability to design effective stabilization and remediation strategies.