Characterisation of the polyethylene glycol impregnation of the Swedish warship Vasa and one of the Danish Skuldelev Viking ships

Abstract

The Swedish 17th century warship Vasa and the Danish Skuldelev Viking ships from the 11th century were impregnated with polyethylene glycol (PEG) in the 1960s. The molecular weight, amount and integrity of this PEG were investigated at a range of depths below the wood surface. Large amounts of PEG could be extracted from degraded parts of the ships but hardly any from sound parts. Mass spectrometry showed that PEG 4000 is present only in the surface layers of the wood, PEG 1500 and PEG 600 are present at all depths of the wood that has been treated with it. Low molecular weight PEG was detected in one of the Skuldelev ships by mass spectrometry and Size Exclusion Chromatography (SEC), it is argued that this is due to degradation of PEG 4000. SEC also showed that PEG 600 is the major PEG component in the Vasa which makes this particular object sensitive to changes in air humidity since PEG 600 is hygroscopic.