Painting Layers on Stone: Study of an Early Middle Ages High-relief

Examples of painted layers on statues, bas-reliefs and other architectural elements have been discovered in the course of conservation works in last decades. In most of the cases painting layers are in the state of remnants because of decay mechanisms, soiling, and invasive cleaning. Nevertheless, these colour relics witness ancient pictorial techniques, and contribute to define a symbology, an iconography, and the importance of stone elements in a complex building. An important high relief representing the figure of St. Siro, who is traditionally said to have been the first bishop of Pavia during the 1 century, but probably lived during 4 century, is conserved in Sts. Gervasius and Protasius Church in Pavia. The high-relief, a limestone slab of about 116 x 49 cm, was covered by a lime wash light-brownish in colour, probably imitating other stone elements in the Church façade, at the center of which the sculpted slab was embedded in the masonry till 1861. After then the slab was recovered in an inner chapel where conservation works were recently carried out, taking the staring point for an analytical survey. A careful cleaning, carried out with distilled water heated up to 30 °C, highlighted the presence of polychrome surfaces, which have been analysed by means of optical microscopy, SEM-EDS, and Micro-Raman (μRaman) techniques with the aim to characterise both pigments and grounds. Moreover, a petrographic characterisation allowed to identify the nature of the stone substrate. The data obtained will be used by archeologists and art historians to understand better the provenance of the San Siro high-relief. Actually, it could be hypothesized that it comes from late Roman period, having been reused during early middle ages centuries, when it was partially re-sculpted and painted. INTRODUCTION A high-relief representing the figure of St. Siro, located in a chapel dedicated to this saint in the church of Sts. Gervasio and Protasio in Pavia (in Lombardy region – Italy), has been recently subjected to a careful restoration intervention. The high-relief, consisting of a single piece of stone, which is 116 cm high, 49 wide and 20 cm deep including 3 cm of a background slab, was covered with light-brownish lime wash layer that hampered the legibility of the artwork. This layer was removed by gentle swabbing with the tepid water (30 °C). The restoration revealed an almost integral polychromy applied on the stone elements. San Siro is depicted here wearing a tunic of orange, red and green tones, with a crosier in the right hand and a prayer book in the left hand (Fig. 1). The importance of systematic studies on polychrome stone works has been already pointed out in some papers dealing with decorated architectural elements and bas-reliefs all over Europe and especially in France [2, 14, 15] and Italy [11, 13]. Recently polychrome remnants has been recovered and studied in the basilica of St. Ambrogio in Milan [4], which is very close to the town of Pavia. The two Saints Ambrogio and Siro are linked by common historical events, through the Saints Gervasio and Protasio, who is dedicated the church in which the bas-relief is conserved. 9th International Conference on NDT of Art, Jerusalem Israel, 25-30 May 2008 For more papers of this publication click: www.ndt.net/search/docs.php3?MainSource=65