Unveiling the Invisible in Uffizi Gallery’s Drawing 8P by Leonardo with Non-Invasive Optical Techniques

A Performance Comparison of 3D Survey Instruments for Their Application in the Cultural Heritage Field

Thanks to the recent development of innovative instruments and software with high accuracy and resolution, 3D modelling provides useful insights in several sectors (from industrial metrology to cultural heritage). Moreover, the 3D reconstruction of objects of artistic interest is becoming mandatory, not only because of the risks to which works of art are increasingly exposed (e.g., wars and climatic disasters) but also because of the leading role that the virtual fruition of art is taking. In this work, we compared the performance of four 3D instruments based on different working principles and techniques (laser micro-profilometry, structured-light topography and the phase-shifting method) by measuring four samples of different sizes, dimensions and surface characteristics. We aimed to assess the capabilities and limitations of these instruments to verify their accuracy and the technical specifications given in the suppliers' data sheets. To this end, we calculated the point densities and extracted several profiles from the models to evaluate both their lateral (XY) and axial (Z) resolution. A comparison between the nominal resolution values and those calculated on samples representative of cultural artefacts was used to predict the performance of the instruments in real case studies. Overall, the purpose of this comparison is to provide a quantitative assessment of the performance of the instruments that allows for their correct application to works of art according to their specific characteristics.

Non-invasive contactless analysis of an early drawing by Raffaello Sanzio by means of optical methods

Studying highly valuable and fragile Renaissance drawings requires a non-invasive contactless analytical approach. In this work, we study an early drawing by Raffaello Sanzio, one of the most important artists of the Italian Renaissance, realized during his stay in Florence (1504–1508). Our analyses aimed to reveal the features of the paper support significant for its dating, identify and map the drawing media to understand the artist’s technical approach, and document the drawing condition with imaging and single-sited optical methods. Reflectance Vis–NIR multispectral imaging spectroscopy elaborated with False-Colour and Principal Component Analysis provided information about the paper support and the drawing media. Laser scanning micro-profilometry and Optical Coherence Tomography allowed revealing the superficial micro-scale features of the support. The chemical composition of the different drawing materials was characterized by μ-Raman spectroscopy, which provided also some evidence of the conservation history of the drawing. Integration of spectroscopic and imaging data shows that Raffaello used different dry drawing media (carbon-based and Pb stylus) to sketch the figure and then refined the details and shadows with iron-gall ink. The paper presents a methodological approach for the analytical examination of fragile paper artworks.

Special Issue: Application of Materials Science in the Study of Cultural Heritage

The application of advanced techniques to the study of ancient materials has been increasingly demonstrating to be fundamental to a deeper knowledge of artistic and historic artefacts, contributing to their conservation and restoration [...]