Degradation of marine archaeological wood through

acidification

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

SpectrumTall 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 reducedRight 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

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.80

1

2

3

4

5

6

7

8

9

10

sulfate/reduced sulfur vs total amount

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 SarangiSULI & SLAC