Monuments as sampling surfaces of recent traffic pollution

Onsite advanced biocleaning system for historical wall paintings using new agar-gauze bacteria gel

AIMS

This study reports the results of the application of a new agar-gauze biogel system activated with viable bacterial cells to altered wall paintings.

METHODS AND RESULTS

Biocleaning using agar biogel and agar-gauze biogel systems was performed onsite by direct application to altered wall painting surfaces (25-1000 cm² ). The treatments were performed for the restoration of two original Italian sites: (i) at the Vatican Museums, Cristo che salva Pietro dalle acque-La Navicella, a wall painting by Giovanni Lanfranco (1627-1628) and (ii) at Pisa Cathedral Cupola, Incarnato, a wall painting by Orazio Riminaldi (1593-1630) and his brother Girolamo Riminaldi. The novelty of this study is the use of viable Pseudomonas stutzeri A29 cells in an advanced agar-gauze biogel system and the short bio-application contact times of between 3 and 12 h. The historical artworks were altered by lipid and protein residues from past restoration, as confirmed by Py-gas chromatography-mass spectrometry and FT-IR data. The effectiveness of the biological treatment was assessed, and general considerations were discussed.

CONCLUSIONS

The short bio-application contact time of advanced agar-gauze gel activated with viable P. stutzeri cells makes this biotechnology promising as an alternative method to the traditional onsite cleaning techniques currently in use for altered historical wall paintings.

SIGNIFICANCE AND IMPACT OF THE STUDY

In this study, we report for the first time the biocleaning of altered materials located in vertical and vaulted areas using agar-gauze biogel with short application times. These findings are of great significance for future restoration activities and are crucial for determining the best preservation strategies in this field.

Chemically and size-resolved particulate matter dry deposition on stone and surrogate surfaces inside and outside the low emission zone of Milan: application of a newly developed "Deposition Box"

The collection of atmospheric particles on not-filtering substrates via dry deposition, and the subsequent study of the particle-induced material decay, is trivial due to the high number of variables simultaneously acting on the investigated surface. This work reports seasonally resolved data of chemical composition and size distribution of particulate matter deposed on stone and surrogate surfaces obtained using a new method, especially developed at this purpose. A "Deposition Box" was designed allowing the particulate matter dry deposition to occur selectively removing, at the same time, variables that can mask the effect of airborne particles on material decay. A pitched roof avoided rainfall and wind variability; a standardised gentle air exchange rate ensured a continuous "sampling" of ambient air leaving unchanged the sampled particle size distribution and, at the same time, leaving quite calm condition inside the box, allowing the deposition to occur. Thus, the "Deposition Box" represents an affordable tool that can be used complementary to traditional exposure systems. With this system, several exposure campaigns, involving investigated stone materials (ISMs) (Carrara Marble, Botticino limestone, Noto calcarenite and Granite) and surrogate (Quartz, PTFE, and Aluminium) substrates, have been performed in two different sites placed in Milan (Italy) inside and outside the low emission zone. Deposition rates (30-90 μg cm^-2 month^-1) showed significant differences between sites and seasons, becoming less evident considering long-period exposures due to a positive feedback on the deposition induced by the deposited particles. Similarly, different stone substrates influenced the deposition rates too. The collected deposits have been observed with optical and scanning electron microscopes and analysed by ion chromatography. Ion deposition rates were similar in the two sites during winter, whereas it was greater outside the low emission zone during summer and considering the long-period exposure. The dimensional distribution of the collected deposits showed a significant presence of fine particles in agreement with deposition rate of the ionic fraction. The obtained results allowed to point out the role of the fine particles fraction and the importance of making seasonal studies.

A cheap protocol for colour measure and for diagnostic in planning a cultural heritage restoration. Case study: main façade of Palazzo Governi (Cagliari, Sardinia, Italy)

Due to the bad state of conservation, "Palazzo Governi", a seventeenth-century building located in the old town district of "Stampace" in Cagliari (Sardinia, Italy), was subjected to restoration. Thus, according to the Italian Law n. 1089, the main façade colour must be reproduced, and therefore, its identification was required. The available samples looked fairly degraded, in particular as an easy plaster to crumble; so, some other analyses able to identify the degradation cause were performed. Two different approaches were adopted to attain the first goal, the visual colour assessment by a sensory panel (subjective) and the instrumental measurement by colorimetry (objective). Ion chromatography and inductively coupled plasma-optical emission spectroscopy analyses, as well as conductivity and pH measurements, were performed to evaluate the presence of water-soluble salts inside the plaster, as possible cause of degradation; the binder/aggregate ratio was also evaluated. A full mineralogical and petrographic characterisation of the materials constituting the samples, as well as the identification of their stratigraphy and some other morphologic and structural features suitable to highlight eventual forms of degradation, were performed by optical microscopy. Scanning electron microscopy coupled to X-ray microanalysis was been also used in order to confirm and/or to integrate data obtained by optical microscopy. The samples have been compared with two samples coming from two other buildings, also located in Sardinia, that looked in good conservation state. The results evidenced that the causes of degradation come from a high salt (especially sulphate) content and a scarce presence of binder in the plaster that can be imputed to a wrong initial composition and/ or to a leaching by acidic rain.