Chemical characterisation of degraded wood in ships discovered in a recent excavation of the Etruscan and Roman harbour of Pisa

Abstract

The discovery of several shipwrecks during a recent excavation of the Etruscan and Roman harbour of Pisa (Tuscany) gives a rare opportunity to investigate archaeological woods buried for centuries under wet and anoxic sediments. Botanical analysis shows evidence of a variety of species of wood that were used in these ships with respect to others reported in literature. Chemical analysis was performed on wood of two ships, C and L (I cent. A.D. and II cent. B.C., respectively), using the international standard methods of wood analysis TAPPI and other instrumental methods such as XRD, GC–MS, FT-IR. Comparison with recently cut reference wood species points to drastic degradation since the holocellulose contents are reduced to very low values and lignin contents exhibit consequently marked increases. Crystallinity evaluation of residual cellulose shows that its degradation has occurred with an ordinate mechanism. Inorganic content is very high with respect to literature: the most abundant elements are Ca, and Fe, mostly associated with sulphates; Fe is also present as amorphous oxides. Organic extractive composition and cation exchange capacity measurements give evidence of oxidative degradation of lignin. From chemical composition of wood of ships C and L, it can be inferred that the Pisan ships are degraded to a greater extent than others like the Hanse Coge, the Mayence Roman Ship and the Mary Rose reported in the literature. The collected data are also useful for the choice of consolidation and stabilisation methodologies of wet wood.