Petrographic, biological and chemical techniques used to characterize two tombs in the Protestant Cemetery of Rome (Italy)

In this multidisciplinary contribution, several diagnostic tests were carried out in order to characterize the stone materials, forms of alteration, and protective products applied in the past to two monumental tombs located in the Protestant Cemetery of Rome (Italy). The Protestant Cemetery is a very important historic site, and has been included in the List of 100 Most Endangered Sites in the World since 2005. In this work, two of its tombs were studied: those of Karl (or Charles) Brjullov, a Russian painter who lived in the first half of the nineteenth century, and of Lady Elisa Temple, wife of the artist Sir Grenville Temple. The tombs are both made of white marble and travertine, and the same forms of alteration and degradation, such as blackish biological patinas, black crusts, and chromatic alterations, were found on both monuments. Petrographic analysis of the different lithotypes made it possible to determine textural characteristics, evaluate the state of preservation, and formulate some hypotheses about their provenance by means of oxygen and carbon isotopic ratios, and evaluation of maximum grain size (MGS) and shape preferred orientation (SPO) of calcite grains. Laboratory culture analysis identified autotrophic species and, in some cases, black patinas caused by fungal species were found. Lastly, Fourier transform infrared spectroscopy (FT-IR) revealed that some synthetic protective products had been used in previous, undocumented restoration processes on some portions of both graves.