Abstract
The wood finish of historical bowed string musical instruments made in Cremona (Italy) during the seventeenth and eighteenth century is a complex multi-layered coating system, where varnishes and other organic binders are variously mixed with inorganic fillers and pigments. It consists of several layers with reduced thickness (tens of microns or less), hard to be distinguished due to the similarity of the constituent materials. Nevertheless, the identification of chemical and morphological features (layering and boundaries) is strictly necessary to disclose the traditional manufacturing procedures. In this paper, we propose an innovative protocol to fully characterize such a multi-layered coating system by combining hyperspectral photoluminescence (PL) micro-imaging with μFTIR-ATR mapping and SEM-EDX analysis. The protocol has been employed to study three cross-sectional samples from violins made by Lorenzo Storioni (second half of eighteenth century), whereas a properly reproduced laboratory mock-up was used to set the analytical protocol. The obtained results demonstrate that the combination of these complementary spectroscopy mapping techniques in a high-resolution strategy allows one to clearly identify the morphology of a few microns thin layers, to assess the penetration depth of sizing treatments into the wood and to detect restoration areas.
Highlights
Bowed string musical instruments made from the sixteenth to eighteenth centuries in Cremona represent a model for current violin makers
The wood finish of historical bowed string musical instruments made in Cremona (Italy) during the seventeenth and eighteenth century is a complex multi-layered coating system, where varnishes and other organic binders are variously mixed with inorganic fillers and pigments
We demonstrated that extremely small differences in the optical properties of the layers can be enhanced by combining the high spectral resolution of the technique with the multivariate statistical approach
Summary
Bowed string musical instruments made from the sixteenth to eighteenth centuries in Cremona represent a model for current violin makers. Driven by the rediscovered value of tradition and the musicians’ commitment, the investigation and the characterization of historical musical instruments became a matter of study starting from the 1950s of the last century [1]. To transform a bare wood into a ready-to-play instrument, the wood surface is subjected to a series of chemical treatments that turns it into a complex multi-layered coating system in which inorganic micrometric particles (pigments, fillers) are variously mixed with organic binders and varnishes. As described in previous works [2], wood is usually pre-treated with a protein-based layer (e.g., animal glues or caseinates) to seal the wood pores and prepare the surface for the application of the varnish. Mineral siccative agents (e.g., lead) and pigments (e.g., iron earth, madder lake) can be included [6,7,8]
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