Integrated approach to the characterization and conservation of artefacts of the Brazilian colonial period

Several common-use artifacts (coins, faience, cult objects, etc.) coming from two excavations sites near Rio de Janeiro, two sugar farms Historico do Rochedo and Cruzeiro, have been the subject of this investigation, which aimed to integrate physico-chemical characterizations with the identification of degradation mechanisms, and the proposal of innovative conservation methods, such as PECVD deposition of SiO2-like films for protection of metallic artifacts. For the microchemical, micromorphological and microstructural analysis, optical microscopy-OM, X-ray diffraction XRD, X-ray fluorescence-XRF, and scanning electron microscopy equipped with electron microprobe-SEM + EDS have been employed. A cleaning step followed by a consolidation step has been carried out on glassy artefacts, while on metallic artefacts the mechanical cleaning has been followed by a stabilization treatment when necessary. For long-term protection the deposition by PECVD of SiO 2-like films has been performed on a series of copper-based alloys in a home made reactor fed with an tetraethoxysilane-oxygenargon mixture. The coatings show a good barrier effect against the diffusion of water and oxygen from the environment to the metal surface, that increases with increasing the oxygen to monomer ratio in the feeding gas mixture and the input power density. Moreover, the coating adhesion increases if the deposition process is performed after a hydrogen plasma treatment.