Protective effect of linseed oil varnish on archaeological wood treated with alum

This unusual pattern of wood degradation was not mirrored by the inorganic components: alum was found to be more abundant at the surface of the fragment than at depth, as would be expected, but no decomposition products were found. However, the alum appeared to mainly consist of ammonium salt, rather than the potassium alum documented as the treatment material for the Oseberg artefacts.