Sara Goldman SULI Summer Internship August 12, 2010

The sulfur problem Sulfuric acid is appearing on museum artifacts These pieces have already been extensively treated to preserve them Widespread issue in the archaeological community

The sample Sample from the stem post timber Mary Rose, warship of King Henry VIII Sank in 1545, excavated 1981

What are we looking for? What types (species) of sulfur are in the wood? Which species are becoming acidic? Where is it coming from? Can we stop it?

X-ray Absorption Spectroscopy Bohr model of the atom X-ray bombardment Each electron shell requires a very specific energy

XAS graphical results Spectrum Tall peak, “edge” Additional structure, “near edge” Edge jump

Advantages of XAS XAS is a very sensitive detector, it can find small amounts of specific items It can detect differences in oxidation state and structure

Identifying species with XAS Your unknown contents are like a finger print You must compare them to prints that are already on file to identify what you have

The spectra Previous studies have shown uniform sulfur content Our 15 positions on the same piece differ wildly

Observing total sulfur and sulfate content Edge jumps indicated some locations had up to x3 as much total sulfur as their neighbors The amount of oxidized sulfur differed dramatically

Oxidized sulfur The flatter lines indicate aqueous sulfate The distinct features indicate an ordered molecule

Fitting the data A library of sulfur standards was created to fit our sample spectra Left is most reduced Right is most oxidized

Sample fit All 15 spectra were fit to the sulfur standards This sample contains at least 5 sulfur types Missing information on additional structure.

Information from the fits There is a correlation between the amount of total sulfur, and the amount of oxidized sulfur

How does elemental sulfur get into the wood? Anaerobic bacteria

Focus for future efforts Acknowledge the wide variation in sulfur content for treatment purposes Focus on the species that have the potential to become acidic

Acknowledgements Mentor Apurva Mehta Riti Sarangi SULI & SLAC