Study of materials and techniques in painted ceiling panels from a palace in Cremona (Italy, 15th century)

n/

The exemplary case of a remarkably well-preserved historical musical instrument: the “Tuscan” Stradivari violin (1690)

In recent years, scientific diagnostic analysis has increasingly focused on historical musical instruments, especially bowed stringed ones. The materials composing the stratigraphy of these peculiar works of art are characterized by a complex and heterogeneous nature, which is representative of the working techniques employed by the great violin makers of the past. The entire coating system, so called wood finish [1], includes multiple varnish layers on a previously grounded wooden substrate to prevent varnish penetration. Over the time, however, the original stratigraphy of these centuries-old masterpieces could have been affected by the extended handling during performances and practice, the very close contact of the instrument with the musician skin, or, again, accidents and interventions of maintenance and restoration. As a consequence, variations in its coating thickness and composition have most often occurred. The object of the present study is one of the best-conserved instruments by Antonio Stradivari, namely the “Tuscan” violin (1690) today preserved at the Accademia of Santa Cecilia in Rome (Italy). Commissioned by the Medici family in 1684, as a part of the famous quintet, it is one of the earliest examples of the master’s multiple-layer varnishing method [2]. The remarkably well-preserved wood finish of the violin was non-invasively studied by UV-Induced Fluorescence (UVIFL) photography (by B. Brandmair), Fourier-Transform Infrared (FTIR) reflection spectroscopy and X-Ray Fluorescence (XRF) spectroscopy. The hypothesis drawn from the non-invasive approach was supported by a micro-destructive analysis performed on two micro-samples, one taken from the violin’s top plate (Fig. 1) and the other from the centre bass rib. The micro-samples were analysed by the Optical Microscope (OM) equipped with visible and ultraviolet lights and by the Scanning Electron Microscope (SEM) coupled with Energy Dispersive X-ray (EDX) spectrometer. The aim of the multi-analytical investigation was the characterization of varnishes, pigments and wood treatments constituting the violin’s stratigraphy, trying to understand the methods used by Antonio Stradivari to finish the instrument. From the results, the varnish is confirmed to be applied in a two-layer system: the uppermost salmon-fluorescent coloured varnish (Fig. 1, level A) is oil-resinous composed, with crystals of calcium oxalates witnessing the age of the varnish as a decomposition product of lipid materials [3]; the lowermost yellow-whitish fluorescent layer (Fig. 1, level B) is also characterized by an aged oil-resinous varnish with an aluminium- and oxygen-rich grain dispersed therein which gives rise to possible attributions, including that of alumina (Al2O3) as a substrate for lake pigments [4]. At the interface between the wood and the overlying varnish (Fig. 1, level C), probably related to a wood treatment, a proteinaceous compound can be likely identified as a binder of a few silica and silicates mineral phases. Moreover, rare particles of possible titanium-manganese-iron oxides and/or hydroxides as well as iron-containing aluminosilicates, both suggesting the possible presence of iron-based pigments such as red-ochre or umber earth [5], were found at this level. Under the treatment level, finally, small amounts of chlorine, sulphur, potassium and calcium could be ascribed to a wood pre-treatment method [2]. In conclusion, by combining data from the non-invasive and micro-destructive analytical campaign it was possible to propose a stratigraphic hypothesis of the “Tuscan” violin

Improving Wood Resistance to Decay by Nanostructured ZnO-Based Treatments

In this study, the maple wood surface was coated with nanostructured zinc oxide, grown on the surface by using a hydrothermal process, and furtherly treated with shellac varnish. Samples obtained both after ZnO treatment and after the final varnish application were characterized by different techniques, i.e., X-ray diffraction (XRD), scanning electron microscopy combined with energy-dispersive X-ray spectroscopy (SEM-EDS), micro-FTIR with attenuated total reflectance (μ-ATR-FTIR), chromatic variation measurements, and contact angle determinations. Analytical results showed that the wood surface was covered by quite a homogeneous array of inorganic nanoparticles and that the natural resin forms a regular film over the ZnO nanostructures. An accelerated aging test was used to evaluate the protecting effectiveness of the treatments towards UV-induced decay of wood material. After the test, wood treated with ZnO and with the shellac/ZnO combination underwent a considerably lower chromatic change if compared to the untreated wood, suggesting an enhanced resistance of the treated maple to the decay due to light exposition. The presence of nanostructured ZnO protects from decay not only the wood substrate but also the shellac film. A microbiology test showed that growth of fungal species, e.g., common mold, is prevented on the wood surface treated with ZnO or with shellac/ZnO, indicating that the nanostructured zinc oxide also provides an effective protection from biodeterioration. The coating obtained by consecutive application of nanosized ZnO particles and shellac varnish combines the excellent aesthetical features and water repellence of the traditional finish with the protecting effectiveness of the nanostructured inorganic component

Bistren cryptands and cryptates: versatile receptors for anion inclusion and recognition in water

Bistren cryptands can act as selective anion receptors in water in two distinct versions: as hexaprotonated cages and as dicopper(ii) cryptates. Both classes of receptors exert geometrical selectivity, but dimetallic cryptates establish the strongest interactions with the anion

A two-channel Molecular dosimeter for the optical detection of copper(II)

A cyclam-like macrocycle with an integrated push-pull chromophore selectively detects Cu2+ inclusion through both orange-to-yellow colour change and quenching of the green fluorescence

“I Cantieri del Suono” project: a public-private cooperation for the valorization of the violin “Piccolo” by Lorenzo Storioni (1793)

The Cultural District of Violin Making is a network of Cremona municipality that keeps the search for quality violinmaking alive and constantly strives to defend traditional craftsmanship. It coordinates various groups in the city involved in education, teaching and research in the field of music and violinmaking. The Bracco Foundation, one of the leading arts patrons in Italy, has chosen to finance the “I Cantieri del Suono” project, dealing with this highly promising area. One of the projects aims consists in the acquisition and valorisation of a rare violin made by Lorenzo Storioni (Cremona, 1744-1816), involving all the main organisations in the District, plus the violin makers that work in the city of Cremona. This small-size violin, known as “Piccolo”, was probably made for a child. The instrument was played in the decades following its construction (1793), but then it has not been used for a significant period. It provides an extraordinary piece of evidence when it comes to construction techniques, the materials used and the composition of varnishes in late eighteenth century Cremona. The analytical protocol developed at the Laboratorio Arvedi di Diagnostica non Invasiva allowed collecting new data on the instrument through a non-invasive approach (XRF and FTIR spectroscopy, X-ray radiography, VIS-UVIFL photography, 3D laser scanning, OCT, NMR). The obtained results were discussed with the students of the Master’s degree in Conservation and Restoration of Cultural Heritage, aiming at identifying the best procedures to preserve the instrument and its materials. Meanwhile, the students of the International School of Violin Making took advantage from 3D model, making a playable copy of the instrument. The violin and its copy will soon enrich the Civic Collections and will be exhibited at the Museo del Violino in Cremona. Up to now different strategies of communications have been put in place (publication of a monography, social network notifications, congress for experts in the field). During the exhibition, attention will be given to the diagnostic results, accompanying visitors through different levels of technical insights

Terpyridine derivatives functionalized with (hetero)aromatic groups and the corresponding Ru complexes: synthesis and characterization as SHG chromophores

Push–pull terpyridine derivatives were synthesized and characterized in order to study the variations produced in their optical and electronic properties by linking different (hetero)aromatic electron donor moieties at position 4 of the electron deficient terpyridine moiety. The final donor-acceptor systems were synthesized in fair to good yields by Kröhnke condensation of the precursor aldehydes, with 2-acetylpyridine. Hyper-Rayleigh scattering in dioxane solutions using a fundamental wavelength of 1064 nm was employed to evaluate their second-order nonlinear optical properties. Terpyridine derivative functionalized with the 9-ethyl-9H-carbazolyl group exhibited the largest first hyperpolarizability (beta = 610 × 10-30 esu, using the T convention) thus indicating its potential application as a second harmonic generation (SHG) chromophore. Terpyridine derivatives were also used as ligands for the synthesis of novel [RuII(tpy)(NCS)3]– complexes, prepared in good yields by a two-step procedure involving the preparation of [RuIII(tpy)(Cl3] as precursors. RutheniumII complexes display a broad absorption in the visible range, accounting for their very dark color. Their redox behaviour is mainly characterized by the RuII-RuIII oxidation and by the ligand-centred reduction, whose potentials can be finely tuned by the electronic properties of the aromatic substituents on the terpyridine ligand. Hyper-Rayleigh scattering in methanol solutions using a fundamental wavelength of 1064 nm was also employed to evaluate their second-order nonlinear optical properties.Thanks are due to Fundação para a Ciência e a Tecnologia and FEDERCOMPETE for financial support through Centro de Química (UID/QUI/ 00686/2013 and UID/QUI/0686/2016), and a PhD grant to S. S. M. Fernandes (SFRH/BD/87786/2012). The NMR spectrometer Bruker Avance III 400 is part of the National NMR Network and was purchased with funds from FCT and FEDER. The pulsed laser system was acquired within the framework of the grant (PTDC/CTM/105597/2008) from the Portuguese Foundation for Science and Technology (FCT) with funding from FEDER-COMPETE.info:eu-repo/semantics/publishedVersio

Copper(II) Complexes of Cyclams Containing Nitrophenyl Substituents: Push–Pull Behavior and Scorpionate Coordination of the Nitro Group

The three nitrophenyl–cyclam derivatives (nitrocyclams): 1-(4-nitrophenyl)-1,4,8,11-tetraazacyclotetradecane (2), 1-(2-nitrophenyl)-1,4,8,11-tetraazacyclotetradecane (3), and 1-(2,4-dinitrophenyl)-1,4,8,11-tetraazacyclotetradecane (4), in an MeCN solution, specifically incorporate the CuII ion according to an irreversible process signaled by disappearance of the yellow color for a concentration c < 1 × 10–4 M and by a yellow-to-red color change for c ≥ 1 × 10–3, and must be considered efficient and specific dosimeters of copper(II) salts. When present in the ortho position of the nitrophenyl substituent, the −NO2 group coordinates the CuII according to a scorpionate mode, while the metallocyclam system exhibits a trans-I configuration. In an MeCN solution the red trans-I-[CuII(3)]2+ and trans-I-[CuII(4)]2+ scorpionate complexes slowly convert into the violet trans-III scorpionate complexes. Kinetic aspects of the trans-I-to-trans-III configurational rearrangement were investigated in detail for the [CuII(4)]2+ system. In particular, the conversion is spectacularly accelerated by catalytic amounts of Cl–, NCO–, and F–. While for Cl– and NCO– the effect can be associated with the capability of the anion to stabilize through coordination a possible dissociative intermediate, the amazingly powerful effect of F– must be related to the preliminary deprotonation of one N–H fragment of the macrocycle, driven by the formation of the HF2– ion. Most of the metal complex species studied in solution were isolated in a crystalline form, and their molecular structures were elucidated through X-ray diffraction studies. This study documents the first examples of effective metal coordination by the nitro groupThe financial support of the Italian Ministry of University and Research (PRIN−InfoChem) is gratefully acknowledgedS

Stradivari's Varnish Revisited: Feature Improvements Using Chemical Modification

The most widespread varnish formulations used by master violin-makers of the "Italian Golden Age", including Antonio Stradivari, were based on mixtures of siccative oils (e.g., linseed oil) and natural resins (e.g., colophony). Similar formulations are still used for the finish of contemporary instruments. Although most precious violins made by Stradivari and other Cremonese Masters are kept in museums, several instruments are still played and their finish may undergo deterioration due to contact with the players. Moreover, the decay of the traditional varnish may occur due to mechanical stress and natural aging caused by environmental agents (e.g., exposure to uncontrolled light, humidity, and temperature changes). The main aim of this research work is to investigate the possible improvement of varnish resistance to the decay induced by different aging processes. For this purpose, the traditional varnish (linseed oil/colophony 3:1 w/w) was recreated in the laboratory following an ancient recipe and then it was functionalized with a cross-linking agent (3-Glycidyloxypropyltrimethoxysilane, GLYMO). Plain and functionalized varnishes underwent artificial aging (UV light, temperature, and humidity variations), and their properties were comparatively studied using different techniques. All the results suggest that the functionalized varnish displays improved resistance to the aging process and particularly enhanced photostability and increased hardness (resistance to scratches)

ZrO2-doped ZnO-PDMS nanocomposites as protective coatings for the stone materials

ZnO is a semiconductor that has found wide application in the optics and electronics areas. Moreover, it is widely used in different technological areas due to its beneficial qualities (high chemical stability, non-toxicity, high photo-reactivity, and cheapness). Based on its antibacterial activity, recently it has found also application to prevent bio-deterioration of cultural heritage buildings. As many authors suggested, doped ZnO nano-structures exhibit better antibacterial properties than undoped analogues. In the present work, ZnO nanoparticles doped with ZrO2 have been prepared by a sol-gel method in order to enhance the photocatalytic properties as well as the antibacterial activity of ZnO. Then, ZrO2-ZnO-PDMS nanocomposite (PDMS, polydimethylsiloxane used as the binder) was synthesized by in-situ reaction. The resulting nanocomposite has been investigated as a possible protective material for cultural heritage building substrates. The performances of newly prepared coating were evaluated in three different stones (Lecce stone, Carrara Marble and Brick) and compared with Plain PDMS as a reference coating. </p