Degrado e problematiche conservative di un dipinto ad olio su pietra a Malta

Abstract

This article provides a sumtnary of the diagnostic study undertaken on an oil-based painting on a dome of a church in Malta. Painted in 1903 and extensively restored in 1963, this mural is now found to be in an appalling condition. To investigate causes and processes of deterioration, a multidisciplinary approach was followed. This included historical research, non-invasive examination, sampling and analysis, and environmental monitoring. Soluble salts, mainly gypsum and minor amounts of halite, were found to be the main causes of deterioration. Salt crystallization cycles were triggered by recurrent and prolonged rainwater infiltrations, whilst solar radiation may have played a role by increasing the number of crystallization cycles. Deterioration was also favoured by intrinsic factors. Oil-based paintings applied to porous materials, in this case a very porous limestone, create a barrier to the passage of water, and favour the formation of an interface between the wall and the paint layer, under which salts may crystallize. In this case, the artist applied his painted strata over pre-existing paint layers making the painting's structure even more prone to delamination. The limestone over which the painting was applied was found of bad quality and susceptible to salt decay. The difficult issues in relation to the preservation of this painting are referred to and are open for discussion.