Sulfur and iron in shipwrecks cause conservation concerns

Area of Science:

• Materials Science
• Archaeological Science
• Chemistry

Background:

• Marine-archaeological wood, like that from the Vasa and Mary Rose shipwrecks, accumulates significant organosulfur, pyrite, and iron(II) sulfides when preserved in seawater.
• In museum environments, the oxidation of these sulfur compounds, particularly in the presence of iron ions, leads to severe acidity within the moist wood.
• This acidity poses a significant threat to the long-term preservation of these invaluable historical artifacts.

Purpose of the Study:

• To review and discuss advancements in conservation methodologies for marine-archaeological wood.
• To address the challenges posed by acid and iron accumulation and sulfur compound degradation.
• To provide insights into the analysis and stabilization techniques for sulfur compounds in waterlogged wood.

Main Methods:

• Synchrotron-based sulfur X-ray absorption spectroscopy was employed to identify and quantify sulfur species.
• Analysis of organosulfur compounds, pyrite, and iron(II) sulfides in archaeological wood samples.
• Review of existing and emerging conservation treatments for acid and iron removal.

Main Results:

• Demonstrated considerable accumulation of organosulfur (e.g., thiols), pyrite, and iron(II) sulfides in marine-archaeological wood.
• Identified the potential for severe acidity generation due to sulfur compound oxidation in museum conditions.
• Highlighted the critical role of iron ions in exacerbating the degradation process.

Conclusions:

• Effective conservation strategies must address the removal of both acid and iron from degraded archaeological wood.
• Analysis and stabilization of sulfur compounds are crucial for preventing further deterioration.
• Understanding sulfur chemistry is key to preserving submerged wooden heritage.