The great throughput and sensitivity of the HERA IPERSPETTRALE hyperspectral cameras are extremely useful in the study of works of art, cultural artifacts and cultural heritage, where low-illuminance conditions are mandatory in order not to damage the samples. In this field, the camera has already been used to investigate the attribution and the dating of paintings, to monitor their state of conservation and to assess their authenticity with a non invasive technique.
HERA was employed to analyze a stained glass window. Plates typically exhibit strong absorption bands located at well-defined wavelengths. Since window glass manufacturing has changed throughout time, spectral characterization is a means to determine the composition of glasses and of their coloring agents, to assess the authenticity of ancient windows.
Here a portion of an artistic glass window at Santo Spirito Church in Milan (Italy) was back-illuminated by natural sunlight, and the camera recorded the transmitted light. We observed that blue tiles exhibit different transmission spectra and can be separated into 5 classes. In particular, we identified two blue tiles with negligible infrared transmission.
As another example, we report in the following the results obtained on the “Viterbo Crucifixion”, a 16th century panel oil painting exposed in the Museum of Colle del Duomo in Viterbo (Italy), and whose attribution is still under debate. These measurements have been performed in collaboration with the University of Tuscia, the CNR (Consiglio Nazionale delle Ricerche), and Politecnico di Milano University.
In Figure 1, the colour image of the painting is reported for reference, together with the reflectance spectra of the selected areas. In such applications, the capability to measure the spectra of such a richness of colours makes the HSI technique a powerful method to gather precious details on the pigments employed by the painter, thus providing valuable insights for conservation and dating science. In this case, the reflectance data reveal the presence of precious ultramarine blue and vermillion pigments, attesting the importance of the committer.
Figure 1: Colour image of the painting with reflectance spectra of selected areas, revealing ultramarine blue and vermillion pigments.
One of the most fascinating features of this painting is related to the figure of St. John, whose face is reported in the figures below. In fact, one can clearly notice that it has a female aspect when observed in the red-near infrared region (e.g. at 650 nm, see below), but it assumes more masculine traits and a hollowed aspect when observed in the UV-blue region (e.g. at 450 nm, see below). This behavior, which seems to be intentional as it occurs only in the face of St. John, represents one of the key elements to attribute the painting to Michelangelo.
C. Pelosi et al., “Beyond the visible: The Viterbo Crucifixion panel painting attributed to Michelangelo Buonarroti”, Microchemical Journal, Volume 154 (2020)
