The Bremen Cog of thirteenhundredandeightyen1380 - an electron microscopic study of its degraded wood before and after stabilization with polyethylene glycoöenPEG

The Bremen Cog is a big ship built AD 1380 from oak wood. After its recovery from the river Weser, the waterlogged ship’s timbers were successfully stabilized using a novel two-step polyethylene glycol (PEG) treatment. An electron microscopic study of the patterns of degradation and of the distribution of PEG within the Cog wood is described. Descriptions like these do not exist for many well known archaeological objects. SEM revealed that in areas with extensive degradation, wood cell walls are thinned and cells have a distorted appearance. TEM provided evidence that the wood has been degraded primarily by erosion bacteria. The stabilization treatment involved impregnation first with PEG 200 and then with PEG 3000. The SEM observations of PEG-impregnated wood revealed that in degraded tissues all cell types are well filled with PEG 3000. Non-degraded tissues are impermeable to PEG 3000 and are impregnated only with PEG 200. SEM confirmed earlier fluorescence microscopic evidence, that PEG 200 is absorbed by the cell walls.