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Abstract
This work deals with the identification of natural binders and the study of the complex stratigraphy in paintings using reflection FT-IR spectroscopy, a common diagnostic tool for cultural heritage materials thanks to its non-invasiveness. In particular, the potential of the near-infrared (NIR) spectral region, dominated by the absorption bands due to CH, CO, OH and NH functional groups, is successfully exploited to distinguish a lipid binder from a proteinaceous one, as well as the coexistence of the two media in laboratory-made model samples that simulate the complex multi-layered structure of a painting. The combination with multivariate analysis methods or with the calculation of indicative ratios between the intensity values of characteristic absorption bands is proposed to facilitate the interpretation of the spectral data. Furthermore, the greater penetration depth of NIR radiation is exploited to obtain information about the inner layers of the paintings, focusing in particular on the preparatory coatings of the supports. Finally, as proof of concept, FT-NIR analyses were also carried out on six paintings by artists working in Lombardy at the end of the 15th century, that exemplify different pictorial techniques.
Highlights
Received: 30 December 2021The analysis of the binders, i.e., the media in which the pigments are dispersed to be spread on the pictorial supports, is an important but demanding task in the field of conservation science.Over the centuries, artists have used a wide range of materials—drying oils, natural gums and proteinaceous materials, such as egg white or yolk, animal glue or milk derivatives—associated with different painting techniques
Since calcium carbonate does not absorb in the NIR region, the only signals observed in this range for the ground layer spectrum for these model samples are due to the animal glue used to prepare it (Supplementary Materials Figure S1)
Various pigments were used in the models, including pigments containing hydroxyl groups and prone to absorb NIR radiation
Summary
Received: 30 December 2021The analysis of the binders, i.e., the media in which the pigments are dispersed to be spread on the pictorial supports, is an important but demanding task in the field of conservation science.Over the centuries, artists have used a wide range of materials—drying oils, natural gums and proteinaceous materials, such as egg white or yolk, animal glue or milk derivatives—associated with different painting techniques. The artists experimented with recipes based on mixed binders to improve and modify their pictorial properties or to obtain particular chromatic effects by combining their different characteristics. This is the case, for example, of tempera grassa, an emulsion of oil and egg or, sometimes, oil and casein [1]. Even the preparatory layers, i.e., the coatings spread on the support (typically a wooden panel or a canvas) before the application of the subsequent layers, represent an important aspect in the investigation of a painting They were traditionally made of white mineral substances mixed with an Accepted: 4 March 2022
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