Abstract
Musical instrument coatings are generally made by multi-layered systems of organic and inorganic materials, applied on the wood substrate by the violin makers during the finishing process. This coating has paramount relevance for several aspects: protection from sweat and dirt, increase of specific acoustic features, and especially aesthetic effects. In fact, the colour of historical bowed string instruments represents a very peculiar characteristic of each workshop. Among the various colourants, lakes are the most challenging to detect because of their sensibility to the alteration processes. In this work, non-invasive and micro-invasive procedures were applied to a set of mock-ups mimicking historical coatings systems prior and after artificial ageing, in order to highlight the overall information that can be recovered for the detection of madder lake in historical bowed instruments. A set of techniques, including colourimetry, visible and UV-light imaging, stereomicroscopy, Fibre Optics Diffuse Reflectance spectroscopy (FORS), X-ray Fluorescence spectroscopy (XRF), Scanning Electron Microscopy coupled with Energy-Dispersive X-ray microprobe (SEM-EDX), and Fourier-Transform Infrared spectroscopy (FTIR) were used in order to evaluate the pros and cons in the detection of organic and inorganic component of madder lake at low concentration levels.
Highlights
In the last decades, scientific studies of historical musical instruments have provided relevant information about the materials used by the Masters of the past and their construction procedures.In particular, the development of non-invasive and micro-invasive analytical methods have given impetus to the instrumental detection of the materials employed in the “finishing process”, consisting in coating systems made by superimposed layers of organic and inorganic materials [1,2].The aesthetic appearance of the coatings is determined by the optical features of the materials used in the finishing layers, and by the colourants in particular
A set of techniques, including colourimetry, visible and UV-light imaging, stereomicroscopy, Fibre Optics Diffuse Reflectance spectroscopy (FORS), X-ray Fluorescence spectroscopy (XRF), Scanning Electron Microscopy coupled with Energy-Dispersive X-ray microprobe (SEM-EDX), and Fourier-Transform Infrared spectroscopy (FTIR) were used in order to evaluate the pros and cons in the detection of organic and inorganic component of madder lake at low concentration levels
Even if the selective FORS signals of the dye are maintained for longer time of the lake spread under a varnish layer is less prone to fade, as it has been highlighted by the exposure under artificial solar light in samples where the lake (20% concentration) is spread in oil-colophony varnish (OCV), FORSsignals data. are
Summary
Scientific studies of historical musical instruments have provided relevant information about the materials used by the Masters of the past and their construction procedures.In particular, the development of non-invasive and micro-invasive analytical methods have given impetus to the instrumental detection of the materials employed in the “finishing process”, consisting in coating systems made by superimposed layers of organic and inorganic materials [1,2].The aesthetic appearance of the coatings is determined by the optical features of the materials used in the finishing layers, and by the colourants in particular. Red and orange inorganic pigments such as iron-earth, vermilion or orpiment, were often identified in historical musical instruments [4,5,6] The detection of these pigments is normally achieved by non-invasive spectroscopic investigations [7,8,9], or by micro-analytical techniques—such as micro-Raman spectroscopy or scanning electron microscopy coupled with energy dispersive X-ray analysis—performed on small flakes [10,11]. The identification of lakes is definitely more challenging mainly because natural organic dyes are normally fugitive and occur as minor components of the inorganic substrate. For these reasons, a different analytical approach is often required. As for lakes in finishing layers applied on wood, only a recent paper discusses a multi-technique characterization of three reference madder lakes containing different metal cations [18], which were brushed on wooden panels in order to obtain three-layered systems
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