Giuseppe Sabatini

Determination of damage thresholds to prevent side effects in laser cleaning of pliocene sandstone of Siena

Abstract The present work reports a basic investigation aimed at optimizing laser cleaning interventions on pliocene sandstone of Siena. Irradiation trials were performed with a short free running Nd:YAG laser, on quarry samples and on samples from Palazzo Spannocchi presenting black crust. The physical parameterization associated with a detailed petrographic and mineralogic diagnostics of the induced effects, allowed the irradiation thresholds for damage phenomena to be derived and their nature understood. The experimental results reported here allow the definition of the best irradiation conditions and the laser parameter ranges for a safe and controlled black crust removal from pliocene sandstone.

Laser cleaning methodologies for stone façades and monuments: laboratory analyses on lithotypes of Siena architecture

Abstract The present study was conceived for an evaluation of the effectiveness of laser cleaning techniques applied to samples collected from numerous monumental buildings in the city of Siena (Palazzo Pubblico, Cappella di Piazza, Baptistery, Logge del Papa and Palazzo Spannocchi). All the characteristic lithotypes of Sienese architecture are represented: Montagnola Senese marble, Cavernous limestone, Pliocene sandstone and Red Ammonitic limestone. The tests were devised so as to have the widest variability of situations in relation to the colour and composition of the lithotypes, the state of deterioration of the samples and the level at which to stop the cleaning. The tests were preceded and followed by detailed petrographic analyses. In the introduction to the work, we underline the importance of an accurate reconstruction of the stratigraphy of the external horizon of deterioration of the stone for an appropriate choice of the cleaning intervention; the potential advantages of laser techniques are consequently further emphasized.

Environmental geochemical maps of Italy from the FOREGS database

The Geochemical Atlas of Italy addresses the need for geochemical mapping of the country, based on FOREGS procedures. Data from samples of Italian topsoil, subsoil, stream water, stream sediment and floodplain sediment have been extracted from the FOREGS database and supplemented with data from eight new sample sites. In total 360 geochemical maps have been produced and spatial correlations have been found between the underlying geology and element abundances in the sampled media. The aim of the Geochemical Atlas of Italy is to document background/baseline chemical element variation at the national scale. It is found to be a suitable tool to support government decision-makers to assess trigger and action limits at the local scale, when considered in the light of the complex spatial variability of Italian geology. Maps presented here demonstrate that low density geochemical mapping is a viable tool to obtain an impression of natural element variation at the country scale and to identify areas where more detailed sampling is advisable.

Does salt water intrusion constitute a mercury contamination risk for coastal fresh water aquifers

Four different sampling surveys were carried out in 1998 to evaluate the possible causes of severe mercury contamination involving many wells spread over a vast territory along the coast of southern Tuscany (Italy). Several samples of groundwater and coastal sea water were collected to determine the Hg, Cl, Ar, He and N contents. Anthropogenic or deep-seated sources of the Hg involved in the contamination event can be excluded. The observed coupling of Hg pollution with progressive salt water intrusion along the coastal aquifer indicates a close causal relation between these two phenomena.

Application of a new laser cleaning procedure to the mausoleum of Theodoric

Abstract Within the conservation programme of the mausoleum of Theodoric, located in Ravenna, Italy, we applied a new cleaning procedure based on the use of a recently developed Nd:YAG laser system, suitably equipped in this case with long optical fibre cables for the transmission of laser radiation to work sites on the facade. The intervention of the laser technique was required to complete the cleaning of a decoration surrounding the monolithic dome, after conventional cleaning methods had been applied with unsatisfactory results. Preliminary laboratory analyses on stone samples collected from the dome and subjected to laser treatment indicated that this technique was effective and could fully preserve the lime–Ca oxalate film existing below the thick layer of black crusts. Before starting the operative phase on the mausoleum, it was necessary to solve the practical problem of keeping free access to the monument during cleaning operations, which hindered the location of the laser in close proximity to the sites to be cleaned. This was achieved by preparing long fibre cables (up to 50 m) which permitted the successful completion of the cleaning while leaving the laser body far away from the dome.

Traces of Ancient Treatments on the Stone Materials of the Main Façade of the Siena Cathedral: Glazings (Calcium Oxalate Films s.s.) and Other Finishes

The results of previous works have shown that a decisive contribution to an appropriate resolution of the long-debated topic of so-called “calcium oxalate films” can derive primarily from very detailed studies of extensive and architectonically varied surfaces, such as entire monumental facades. This approach, already successfully utilized for Sienese palaces made mainly of bricks (Giamello et al. 2005; Droghini et al. 2009), is applied here to the facade of the main cathedral in Siena, entirely made with natural stone materials.

The Colour of the Façades in Siena’s Historical Centre: Calcium Oxalate Films on Brickwork of the Fifteenth to Sixteenth Century Palaces

For the last 10 years, we have carried out numerous detailed studies on entire facades of palaces from Siena’s historical centre as scientific support for restoration works. The studies of entire brick facades of thirteenth and fourteenth century palaces in Siena have revealed traces of ancient treatments of the surfaces for aesthetic purposes (Droghini et al. 2005; Nardelli 2005). It was also possible to date these treatments, today appearing as calcium oxalate films, to the time when the facades were built (Giamello et al. 2005).

Advanced information system for the investigation of the deterioration of the floor in the Cathedral of Siena

The preservation and recovery of monuments are hotly debated topics in the field of cultural heritage conservation. In the early 1990s, our group in Siena started a study of the stone materials used in the architecture of Siena. The data were then processed by a GIS (Geographic Information System), which allows one to perform a series of interactive data analyses. An important example of the application of this methodology is the marble floor of the cathedral of Siena, consisting of 58 main scenes framed by decorations, for a total of 2500 m2. The analysis involved: a petrographic study of the main lithotypes used in the scenes and of the various types of deterioration detected; realization of a full digital photo-image and of digital models for the reliefs; identification of anomalies beneath the floor by means of geo-radar and geo-electric instruments; monitoring of thermohygrometric conditions; mapping of the 22 stone varieties employed, their state of preservation (33 types of deterioration) and the previous restoration interventions.