Investigations into the Efflorescence of the Treated Wood of the Iulia Felix Roman Wreck and Effects of Environmental Conditions on Its State

The Iulia Felix is a 2nd century AD Roman wreck discovered on the seabed off Grado in 1986. After being recovered, the hull was dismantled and its components were treated with PEG 4000 at high concentrations and temperatures. The treatment and drying pro-cess were completed in 2003. While awaiting exhibition, the wreck elements were stored in a stockroom, where they were preserved for over 20 years. However, this prolonged storage has introduced new variables. In particular, salt efflorescence has appeared on the surfac-es of some elements, raising concerns about potential further degradation. This made in-vestigating this efflorescence and studying how environmental conditions may affect the state of the treated wood particularly pertinent. The efflorescence was analysed using mi-croanalysis performed with a scanning electron microscope equipped with an energy dis-persive spectroscopy probe (EDS), X-ray powder diffraction (XRPD), and Fourier transform infrared (FTIR) spectroscopy. To verify the effect of climate on the treated material, some samples were exposed to severe but realistic humidity levels of 35% and 85% for an ex-tended period until equilibrium was reached. Analysis of the efflorescence revealed the presence of iron- and sulphur-based com-pounds, namely hydrated ferrous sulphates, calcium sulphate and hydrated iron oxides. This indicates that the ship’s elements had been affected by a corrosion process typically associated with the degradation of metal components. This process begins in a maritime environment and is completed in a humid, oxidative environment following artefact re-covery. Moreover, the presence of PEG in the efflorescence indicates that the artefact un-derwent unforeseen conditions after treatment that caused PEG to migrate to the surface over time. Environmental tests showed that using PEG 4000 for treatment significantly slowed down hygrometric exchange with the environment. However, exposure to a dry climate resulted in limited deformation due to minimal mass change (less than 1% for both mass and surface area), whereas prolonged exposure to a humid environment caused an 11% mass increase (due to water vapour absorption), resulting in a ca. 5% increase in sur-face area. This phenomenon was accompanied by the onset of minor cracks. In some cases, however, the samples fractured. Overall, this work contributes to the ongoing under-standing of the preservation challenges faced by underwater archaeological finds, partic-ularly with regard to treatment with high molecular weight PEG. It highlights the need for continuous monitoring to address degradation and its impact on the structural integrity of the wrecks, and provides a basis for future conservation strategies in museums.