To main content

Alum-treated wood: characterization using infrared spectroscopy and solid state 1h and 13C NMR


The Oseberg find contains a large proportion of hardwoods that had been treated about 100 years ago with hot solutions of alum salts (potassium aluminum sulfate dodecahydrate, KAl(SO4)2 . 12H2O). Today, the wood is characterized by a high acidity (pH 1) and is structurally highly degraded. The observed deterioration is also active. The ‘alum treatment’ was a method of choice for the conservation of highly deteriorated waterlogged archaeological wood found from 1850 – 1950 and has since been replaced by treatment with polyethylene glycols (PEG). The alum treatment has been mainly used in Scandinavia but also in the USA, Japan and other European countries.
Attempts to chemically characterize the alum-treated wood from the Oseberg find is one phase in the research currently being undertaken at the Museum of Cultural History as a part of the Alum Research Project. The ultimate aim of this project is to design conservation re-treatments which will stabilize and strengthen the wood. So far, we have focussed on non-destructive analytical techniques using ATR-FTIR and solid state NMR. Further chemical analyses are planned, using destructive techniques.
Analyses using infrared spectroscopy and solid state 1H and 13C NMR were undertaken on selected alum-treated samples and compared with fresh woods as well as archaeological woods from the same find not treated with alum. The advantages of these analytical techniques lie in the fact that sample preparation is minimal prior to measurement – highly deteriorated wood can be greatly modified by standard sample preparation procedures. These techniques, when used together, give an acceptable level of qualitative structural information regarding the state of the remaining polymers.
Analytical results demonstrated that all alum-treated samples are highly degraded relative to archaeological wood from the same find not treated with alum salts. The non-alum-treated archaeological wood has carbohydrates left, which are highly reduced in the alum-treated wood. 13C NMR can distinguish different lignin types, and has shown that syringyl lignin is more deteriorated than guaiacyl lignin in the most deteriorated alum-treated samples. NMR and FTIR-ATR results also show that remaining polymers in the alum-treated wood, dominated by lignins, are highly oxidized and contain carboxylic groups. This shows that the alum-treatment has caused extensive chemical changes in the wood, resulting in wood with a powdery consistency with almost no structural integrity relative to samples from Oseberg not treated with alum.


Academic lecture




  • Susan Braovac
  • Hartmut Kutzke
  • Sissel Jørgensen
  • Aud Mjærum Bouzga
  • Bjørnar Arstad
  • Eddy Walther Hansen


  • University of Oslo
  • SINTEF Industry / Process Technology

Presented at

Shiprecks 2011




18.10.2011 - 21.10.2011



View this publication at Cristin