Analysis of marble statues from the San Bruno Church (Serra San Bruno, Southern Italy): provenance and degradation

Abstract

This paper illustrates the results of a multidisciplinary study on two white marble statues placed in the San Bruno Church (Calabria—Southern Italy): the ‘Madonna con Bambino’ and ‘San Bruno’ statues. The study, performed by combining different analytical techniques (LA-ICP-MS, CL, SEM-EDS, OM, FT-IR, isotopic ratios of ¹⁸O/¹⁶O and ¹³C/¹²C by mass spectrometry), aims to give information on the provenance of the marble, the kinds and causes of decay forms that affect the surface of the statues, and the materials used during some undated renovation works. As regards the “San Bruno” statue, three past undocumented restoration samples were analysed. Two of these samples were made with a mixture of gypsum and white pigments, while the other one is a mixture of lime mortar and white pigments, with the addition of diatomaceous earth. A comparison of the obtained data with bibliographic studies concerning pigments allowed the formulation of some hypotheses about the renovation works: they were probably carried out after the early 800s. For both statues several analyses were carried out to characterise some yellow–brown patinas present on their bases. Wax and calcium oxalate are the main components of the patinas on the statues: the former attributable to the use of wax candles, the latter, probably due to the alteration of organic matter, which may have been used during previous restoration phases. The Mn content, the maximum grain size (MGS) of calcite crystals and the isotopic analyses (δ ¹³C, δ ¹⁸O) confirmed that Carrara white marble was used to sculpt the two statues and their bases.