Biodeterioration of Pompeian mural paintings: fungal colonization favoured by the presence of volcanic material residues

Abstract

This work was focused on the study of the biodegradation processes jeopardizing a mural painting conserved in the basement of Ariadne House (archaeological site of Pompeii, Italy). The fresco stood out for its peculiar state of preservation: the upper part, recovered in 1988, was just barely colonized by microorganisms. On the contrary, the lower part (excavated in 2005) was almost completely covered by extensive biological patinas. The genomic characterization carried out by polymerase chain reaction (PCR) highlighted the presence of seven different fungi strains on the mural surface. Beside, in situ and laboratory analyses were performed with the purpose of identifying the causes of the heterogeneous spatial distribution of the biopatinas. The in situ Raman spectroscopy and energy dispersive X-ray fluorescence (ED-XRF) spectroscopy measurements excluded any link between the heterogeneous colonization and the original materials present in the wall. On the other side, X-ray diffraction (XRD) and scanning electron microscopy (SEM) on microsamples proved the presence of a thin volcanic material layer overlying the lower part of the fresco. Considering that most of the biofilms of the studied mural painting only growth over these residues, it was confirmed the role of volcanic material as a suitable support for biological colonization. Thanks to the obtained results, this research helped to understand more in depth an important degradation pathway threatening the artworks from one of the most important archaeological sites in the world.

Elucidation of the Chemical Role of the Pyroclastic Materials on the State of Conservation of Mural Paintings from Pompeii

“…The possible risks associated to such pyroclastic deposits have not been studied in depth. However, some recent results suggest that they may also represent a risk that endangers the state of conservation of the wall paintings (namely, possibly acting as nutrient for the proliferation of microorganisms) [2, 3] …”

Understanding the degradation of the blue colour in the wall paintings of Ariadne's house (Pompeii, Italy) by non‐destructive techniques

“…For instance, some rooms show clear evidences of damages provoked by biological colonization (macro and micro) and soluble salts formation (water infiltration, moisture and rain). [ 1,5,7 ] In a few areas (e.g., Rooms 25 and 28), the damages are so critical as to cause the total loss of vast portions of mural paintings. In the case of Room 22 (also called blue room ; Figure 1), these problems are strongly changing the aspect of blue decorations (III style; Figure 2), causing colour variation in some areas (in comparison with the background colour), crystallization of salts as efflorescence and micro‐detachments of painting layers.…”

In-situ multi-analytical characterization of original and decay materials from unique wall mirrors in the House of Gilded Cupids, Pompeii

“…Although volcanic materials from Vesuvius were frequently used in Pompeii (e.g., as aggregate in mortars to improve their mechanical properties [17]), previous studies prove that obsidian can be only formed by the rapid cooling of rhyolitic lava streams, whose typical SiO 2 concentration exceeds 70 wt% [40]. In 2008, Cioni et al [41] presented an interesting study in which the physical and compositional parameters of Vesuvius volcanic materials from recent and ancient times (up to 10,000 years ago) were investigated.…”

“…In this context, the IBeA research group from the University of the Basque Country (UPV/EHU) [11] collaborated with the Archaeological Park of Pompeii, within the Analitica Pompeiana Universitatis Vasconicae (APUV) project [12] by performing research aimed at deepening the understanding of Pompeian remains and providing important guidelines to plan future conservation works. In the past decade, the APUV project has focused efforts for the scientific analysis of artworks preserved in some of the most important residences of the city, such as the House of Marcus Lucretius (IX 3,5/24) [6,[13][14][15][16], the House of Ariadne (VII 4,31/51) [17,18] and the House of the Gilded Cupids (VI. 16.7, 38) [19].…”