Giovanni Guasparri

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.