La Natività, un rilievo ligneo in Valtellina. Storia, restauro, analisi diagnostiche

The Nativity, a wooden relief in Valtellina. History, restoration, diagnostic analysis. The polychromatic and gilt wooden relief representing the Nativity is part of a dismembered altarpiece, datable to the beginning of the 16th century. The restoration work retrieved an elegant gouache gilding as well as the original shades of colour, that were covered by a thick layer of repaint. The intervention was completed by restoring the wooden base. The restoration work was continually monitored through macrophotographs taken by digital microscopy. According to the rules UNI 11118 (2004), the wood species identification was achieved through the anatomical characterization of the cellular elements. Small fragments of wood were taken from hidden parts of the altar, then moistened and cut into the typical directions: the cross, longitudinal radial and longitudinal tangential direction. All samples were found to belong to one species, Scotch pine (Pinus cembra L.), except for one identified as walnut wood (Juglans regia L.). The analyzes carried out mostly by non-invasive protocols, which provided for the succession of optical analysis, diffuse reflectance (FORS) and X-ray fluorescence (XRF), have allowed us to obtain information on the sequence of the restoration works carried out, highlighting, for example, the use of ultramarine Chilean blue on layer originally accomplished with azurite and smalt as glazing.