Surface Stratigraphy on Limestone of Venetian Palaces

The surfaces of Venetian palaces are a testimony to a long history of maintenance. Documents from nineteenth century restoration projects assign dates and reveal some reasons for treatments explaining, for example, the use of aggressive cleaning and then the addition of pigments so that the newly restored façade did not appear ‘too white’. Restoration during the 21st century has presented the opportunity to study the stone surface of three palaces and their stratigraphy. Three types of layers were identified (pollution deposit, silica/wax treatment and corrosion) which overlay the original stone and show distinct elemental signatures. The texture of the outermost deposit showed that the particle size was greatest when it was derived from areas of greatest exposure to the wind compared with calmer sheltered parts. Waxy treatment layers contained strata that probably derived from the brush used to apply the treatment. These treatment layers were warmer in tone than the superficial deposit or underlying stone. Improved understanding of the stratigraphy can inform decisions as to what layers should be protected during restoration.

Figure 4 Ca¢ Rezzonico, Canal Grande, Venice.

Figure 6 Cross-section from Procuratie Nuove sample pp53 with a diagonal orientation with the outside of the stone in the upper right. (a) Scanning electron micrograph showing the presence of a large compact layer on the top of the stone. (b) Mapping of sulfur X-ray intensity from pp53 showing the presence of a thin sulfur-rich corrosion layer beneath the treatment. (c) Mapping of iron X-ray intensity from pp53 showing the borders to the presence of silicon (from the silica treatment). The iron shows the distribution of iron pigment (in this case hematite) in the treatment layer, while the silica borderlines mark the layer of treatment.

Manuela Sgobbi, PhD

Manuela Sgobbi is a researcher in the Department of Environmental Science at the University Ca' Foscari of Venice. Her PhD research focused on the chemical characterization and historical documentation of historic surfaces. She is currently working on a project to remove oil spills from historical surfaces using ‘green’ products.

Peter Brimblecombe, PhD

Dr Brimblecombe is the senior editor of Atmospheric Environment and Professor of Atmospheric Chemistry at the School of Environmental Sciences, University of East Anglia, UK. His main area of interest is atmospheric chemistry, particularly long-term changes in urban air pollution and its effects on health and buildings.

Carlota Sampedro Grossi, PhD

Carlota Sampedro Grossi is a Senior Research Associate at the School of Environmental Sciences, University of East Anglia, UK. Her main area of expertise is petrology, particularly sedimentary petrology and petrophysics. She is researching historic stone decay and the effects of pollution, stone conservation and cleaning treatments, the aesthetics of soiling, and the effect of climate change on buildings and cultural heritage.

Guido Biscontin, PhD

Guido Biscontin is Professor of Chemistry for Restoration, Theory and Techniques for Restoration and head of the Laboratory of Restoration at the University Ca' Foscari of Venice. His research relates to the application of chemistry to cultural heritage, both for diagnosis and the development of new products to protect buildings from decay after cleaning.

Elisabetta Zendri, PhD

Elisabetta Zendri is Professor of Chemistry for Cultural Heritage and Materials for Contemporary Arts at the University Ca' Foscari of Venice. Her main area of interest is the characterization of materials and paths of decay in contemporary art. Her research is focused on the analysis of the materials used by artists and in the restoration of works of art.

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Donhead Publishing 2012