The colour of the facades in Siena’s historical centre: I. Glazings (calcium oxalate films s.s.) and other finishes on the stone materials of the Cathedral’s main facade

This paper focuses on the long-debated topic of the so-called calcium oxalate films: their origin and meaning but also their age and original appearance. The restoration of the main facade of the Siena Cathedral provided a unique opportunity to this end, thanks to the possibility of an extensive and detailed sampling and (as rarely happens) a sufficiently accurate historical knowledge of the construction vicissitudes. This work, mainly based on a polarising microscopy study (coupled with X-ray diffraction and SEM-EDS analyses) of over a thousand thin and ultra-thin sections of 400 microsamples, demonstrates that the current relicts of films are the result of alteration and decay of ancient treatments. In most cases, these were linseed oil-based glazings (the use of this substance is confirmed by historical documents) and pigments. Their role was essentially aesthetic; their use dates the beginning of the fourteenth century and continued at least until the eighteenth century.

Espace,temps et cognition

Revue de Synthèse - La cognition humaine paraît étroitement liée à la structure de l'espace et du temps relativement auxquels le corps, le geste,...     

Effects of Confidentiality-Preserving Geo-Masking on the Estimation of Semivariogram and of the Kriging Variance

Geostatistical methods, such as semivariograms and kriging are well-known spatial tools commonly employed in many disciplines such as health, mining, forestry, meteorology to name only few. They are based essentially on point-referenced data on a continuous space and on the calculation of distances between them. In many practical instances, however, the exact point location, even if exactly known, is geo-masked to preserve confidentiality. This typically happens when dealing with confidential data related to individuals-health and their biometric parameters. In these situations, the estimation of the semivariogram and, hence, the spatial prediction can become biased and highly inefficient. This paper examines the extent of the bias in the particular case when the geo-masking mechanism is known (called “intentional locational error”) and lays the ground to a full understanding of the phenomenon in more general cases. We also examine how the geo-masking affects the estimation of the kriging variance thus reducing the efficiency of spatial prediction. We pursue our aims by developing some theoretical results and by making use of simulated and real data analysis.     

Selinunte (Sicily) and its productive context: the clayey raw materials applied in a long-lived ceramic production (seventh to third century BCE)

The westernmost of the Greek-Sicilian towns, Selinunte, founded in western Sicily during the second half of the seventh century BCE, gives amazing evidences of a historic activity of ceramic production (seventh to third century BCE). The present study aims to identify the raw materials available in the vicinity of the archaeological site of Selinunte, which were possibly used by the ancient potters, and to characterise them by means of petrographic and chemical techniques. A sampling campaign of clays and sands for tempering was undertaken in the archaeological site and the adjacent area. Moreover, locally produced archaeological bricks and tiles were considered helpful for comparison regarding the definition of local ceramic macro- and micro-fabrics and were analysed as well. The comparison between textural, mineralogical and chemical data allowed us to highlight a good similarity between the clayey materials available in the area and the local ancient bricks and tiles. Their compositional resemblance suggests the hypothesis of a systematic use of the studied clays for ceramic productions from the Archaic to the Hellenistic period. The preliminary archaeometric results obtained so far could enhance the distinction between local manufactures and imports and may well lead to the identification of ceramic artefacts produced by the Archaic-Hellenistic workshops of Selinunte at various consumption sites.     

The Enlightenment and the church in the work of Franco Venturi: the fertile legacy of a civil religion

The first part of this essay examines the reasons why the relationship between Enlightenment and religion was central to Franco Venturi's studies on the eighteenth century. In part this came from his own strong secular convictions and from the tradition of secular utopian thought in which Venturi came to intellectual maturity in Turin in the first half of the century, but whose origins lay in the eighteenth century. The essay then explores how these interests guided Venturi's choice to themes and topics, and how his understanding of the relationship changed in the course of his life and writings. The second part of the essay considers Venturi's legacy specifically in relation to this central theme, and discusses the works of subsequent scholars (including the author) whose work has most directly taken up and developed Venturi's own concern to explore the origins of different forms of secular religion in the age of the Enlightenment.     

Historical mortars dating from OSL signals of fine grain fraction enriched in quartz

In the last years the mortar dating through Optically Stimulated Luminescence (OSL) techniques has become a viable support for chronological estimations (date of construction or restoration episodes) of historical buildings. However, the dating of mortar has still open issues mainly regarding the assessment of the bleaching degree of quartz, the analysis of the OSL processes for this type of samples and the need to do appropriate tests for the most correct evaluation of the equivalent dose. This paper discusses the results obtained by OSL dating (blue diode stimulation) on the polymineral fine grain phase, enriched in quartz, extracted from lime mortar samples collected from different sites. Thermal transfer effects, through the behaviour of Equivalent Dose (ED) and recovery tests, degree and time of bleaching were studied. For each mortar sample the adjacent brick was collected; in some cases, sampling of the bricks bracketing a mortar layer was a possibility, thus obtaining a direct comparison with the standard thermoluminescence (TL) dating on the bricks. The results obtained show, for this set of samples, the possibility of dating the mortars through the use of the fine grain fraction provided of a suitable chemical-physical preparation procedure and the verification of the bleaching conditions.