A role for microbial selection in frescoes’ deterioration in Tomba degli Scudi in Tarquinia, Italy

Abstract

Mural paintings in the hypogeal environment of the Tomba degli Scudi in Tarquinia, Italy, show a quite dramatic condition: the plaster mortar lost his cohesion and a white layer coating is spread over almost all the wall surfaces. The aim of this research is to verify if the activity of microorganisms could be one of the main causes of deterioration and if the adopted countermeasures (conventional biocide treatments) are sufficient to stop it. A biocide treatment of the whole environment has been carried out before the conservative intervention and the tomb has been closed for one month. When the tomb was opened again, we sampled the microorganisms present on the frescoes and we identified four Bacillus species and one mould survived to the biocide treatment. These organisms are able to produce spores, a highly resistant biological form, which has permitted the survival despite the biocide treatment. We show that these Bacillus strains are able to produce calcium carbonate and could be responsible for the white deposition that was damaging and covering the entire surface of the frescoes. Our results confirm that the sanitation intervention is non always resolutive and could even be deleterious in selecting harmful microbial communities.

Calcite moonmilk of microbial origin in the Etruscan Tomba degli Scudi in Tarquinia, Italy

“…This observation fits perfectly with the description of moonmilk, indicating that moonmilk was present at the time of tomb discovery and suggesting that the equilibrium of the chemical-physical conditions and the presence of microorganisms in the tomb resulted in the production of moonmilk. Nevertheless, when the atrium chamber was restored, we did not identify moonmilk, but rather a calcite deposit with spheroidal CaCO 3 , on the frescoes 4 . The only exception was the presence of moonmilk in the corner of the western wall in the atrium chamber; in this wall, a window is open to the burial chamber (Fig.…”

“…From June-October 2016 and March-December 2017, the periods of restoration of the central atrium frescoes, we visualized the white deposit on the walls in the Stanza degli Scudi directly with a video microscope (Fig. 2 ) to assess the frescoes; the pictures revealed a white, fluffy deposit with a consistency that differed from that on the central atrium frescoes 4 . This soft deposit was noted in the atrium chamber only in the left corner of the western wall frescoes and on the ceiling.…”

“…The patina is spread over the entire surface on the pictorial layer, and its variable thickness bears no relation to the underlying pigments. By this general assessment, we found that the patina in the Stanza degli Scudi was distinct from the patina that was removed from the atrium chamber frescoes 4 ; this difference prompted the decision to investigate samples from the burial chamber with scanning electron microscopy (SEM). Figure 3 shows pictures of samples taken in March 2017 from the western wall (Fig.…”

“…1b ). In the central atrium, important inscriptions are painted, primarily referring to the great power of the Tarquinian gens Velcha 4 . Moreover, in the same atrium and in the burial chamber, other inscriptions are traced which bear the names of clan members, suggesting family ties and the exact place where the individuals were buried.…”

“…White layers of different consistency were present on the surface of the frescoes; there was a soft deposit (present on the frescoes only in the left corner of the western wall) and a thick and hard layer, which was more difficult to remove. The cleaning of the frescoes was performed using chemical (ionic exchange resins in cationic form, used at pH 5,5 to 6) and mechanical techniques (soft bristle brushes, fibreglass pen and scalpel) 4 .

Figure 1 Etruscan Tomba degli Scudi , Tarquinia, Italy.

…”