A Nanofocused Light on Stradivari Violins: Infrared s-SNOM Reveals New Clues Behind Craftsmanship Mastery.

It is well-known that all the phases of the manufacturing influence the extraordinary aesthetic and acoustic features of Stradivari's instruments. However, these masterpieces still keep some of their secrets hidden by the lack of documentary evidence. In particular, there is not a general consensus on the use of a protein-based ground coating directly spread on the wood surface by the Cremonese Master. The present work demonstrates that infrared scattering-type scanning near-fields optical microscopy (s-SNOM) may provide unprecedented information on very complex cross-sectioned microsamples collected from two of Stradivari's violins, nanoresolved chemical sensitivity being the turning point for detecting minute traces of a specific compound, namely proteins, hidden by the matrix when macro or micro sampling approaches are exploited. This nanoresolved chemical-sensitive technique contributed new and robust evidence to the long-debated question about the use of proteinaceous materials by Stradivari.

Reflection FTIR spectroscopy for the study of historical bowed string instruments: Invasive and non-invasive approaches.

A micro-sample detached from a historical bowed string instrument represents a valuable record of the materials used by the great Masters of violin-making art. It allows researchers to collect a wealth of information and to disclose - at least partially - their procedures for finishing and varnishing. In the present work, a set of four cross-sectioned micro-samples - collected from well-preserved bowed string instruments made by Antonio Stradivari and Lorenzo Storioni - are investigated by Synchrotron Radiation (SR) FTIR micro-spectroscopy in reflection mode. SR-FTIR spectra are discussed both as point analysis and as univariate and multivariate chemical maps. The same cross-sections are also investigated by optical microscopy under UV light and SEM-EDX. Moreover, data obtained directly from the musical instruments by a non-invasive approach employing a portable reflection FTIR spectrometer are also considered. FTIR investigation of the cross-sections is a challenging task for such brittle and complex layered micro-samples. Nevertheless, the high intensity of the analytical SR beam used in reflection geometry allowed us to obtain informative FTIR spectra and to fully preserve the integrity of the samples. Both the non-invasive and the micro-invasive reflection FTIR approaches can reveal the materials spread on the wood surface to finish the musical instruments. The fingerprint of Lorenzo Storioni's production around 1790 emerged from the study of the cross-sectioned samples, definitely different from the technique of Stradivari.

Mid and Near-Infrared Reflection Spectral Database of Natural Organic Materials in the Cultural Heritage Field.

This study presents mid and near-infrared (7500-375 cm-1) total reflection mode spectra of several natural organic materials used in artworks as binding media, consolidants, adhesives, or protective coatings. A novel approach to describe and interpret reflectance bands as well as calculated absorbance after Kramers-Kronig transformation (KKT) is proposed. Transflection mode spectra have represented a valuable support both to study the distorted reflectance bands and to validate the applicability and usefulness of the KK correction. The aim of this paper is to make available to scientists and conservators a comprehensive infrared reflection spectral database, together with its detailed interpretation, as a tool for the noninvasive identification of proteins, lipids, polysaccharides, and resins by means of portable noncontact FTIR spectrometers.

Non-invasive identification of organic materials in historical stringed musical instruments by reflection infrared spectroscopy: a methodological approach.

The analysis of historical musical instruments is becoming more relevant and the interest is increasingly moving toward the non-invasive reflection FTIR spectroscopy, especially for the analysis of varnishes. In this work, a specific infrared reflectance spectral library of organic compounds was created with the aim of identifying musical instrument materials in a totally non-invasive way. The analyses were carried out on pure organic compounds, as bulk samples and laboratory wooden models, to evaluate the diagnostic reflection mid-infrared (MIR) bands of proteins, polysaccharides, lipids, and resins by comparing reflection spectra before and after the KK correction. This methodological approach was applied to real case studies represented by four Stradivari violins and a Neapolitan mandolin.