Laboratory tests addressed to realize customized restoration procedures of underwater archaeological ceramic finds

Abstract

The present contribution is part of a biennial research project funded by the Italian Ministry of Education, Universities and Research (MIUR). This study, currently in progress, deals with innovative experimental approaches applied to the chemical, mineralogical and physical transformations occurring during the prolonged permanence of archaeological ceramic finds in seawater environments as well as to restoration and conservation issues of the same underwater artifacts. The experimental approach used in this research consisted in the manufacture of ceramic test-pieces (briquettes) and their successive placing in underwater environment. This work aims at assessing how textural and compositional parameters along with firing temperatures of a ceramic paste could affect total porosity, pore size distribution and kinetics of capillary water absorption. A further purpose is concerned with the study of the potential modification of porosity and pore size distribution in the same ceramic bodies after immersion in seawater (3 and 6 months). The study was carried out using a multi-technique approach including investigations through polarized light microscopy (PLM), capillary water absorption test, mercury intrusion porosimetry (MIP) analyses and theoretical calculation of salt crystallization pressures. The obtained results show a different behavior of the six experimental pastes as a function of their compositional and textural features as well as pore size distribution and firing temperatures. These parameters, in various extents, have been found significantly influencing the kinetics of water absorption and the susceptibility of ceramic artifacts to salt crystallization processes, with important implications on conservation procedures needed before the musealization.