The stucco decorations from St. Lorenzo in Laino (Como, Italy): The materials and the techniques employed by the “Magistri Comacini”

The paper reports a cross-cutting and systematic approach to the analytical study of Baroque stucco decorations by Italian artists known as “Magistri Comacini”. Samples from the Church of St. Lorenzo in Laino (Como, Italy) were analysed using chemical and mineralogical techniques and the results interpreted with the help of art historians in order to enlighten the artistic techniques. The characterisation of the binder, aggregate and organic fractions was carried out through optical microscopy, scanning electron microscopy with microprobe, X-ray powder diffraction, Fourier transform infrared spectroscopy, gas chromatography-mass spectrometry and laser ablation mass spectrometry equipped with plasma source spectrometry. The results on major, minor and trace components ascertained various recipes. In particular, the investigation of the finishing layers corroborated hypotheses of attribution and chronology and stressed the different skills of the artists working in the building, shedding a light on details of the decoration technique.