A step forward in disclosing the secret of stradivari's varnish by NMR spectroscopy

It is commonly thought that the varnishes used by the great violin-maker Antonio Stradivari may have a role in determining not only the esthetical features but also the acoustic properties of his instruments, and the idea of a "lost secret" is still widespread among musicians and violin-makers. Previous scientific researches on varnish samples of Stradivari's instruments revealed that they were generally made by a mix of linseed oil with and colophony or metal rosinates in different ratios ranging between 75/25 (oil/resin) and 60/40 (oil/rosinate). However, it is still not clear whether the mixture composition can be related to any structural and/or functional feature of the resulting varnish. To investigate this aspect, we prepared varnishes with different linseed oil/colophony (w/w) ratios and applied NMR techniques to achieve information about their chemical-physical characteristics. Here, we show that the two components strongly interact in the solid state and that only the varnish prepared from 75/25 (w/w) linseed oil/colophony mixture displays unique properties in terms of dynamic homogeneity unlike coatings with other compositions. Our results suggest that the so-called "secret" of Stradivari's finish could not be related to unknown ingredient(s) but to a specific oil/resin composition that provides the best performance

Nanoparticles for conservation of bio-calcarenite stone

In the present study, the consolidation effectiveness of some inorganic nanoparticles dispersions (silica, calcium hydroxide, and strontium hydroxide) has been evaluated when applied on a very porous stone substrate, i.e., Lecce stone. The strengthening effect of the nanoparticle-based treatments was compared to that exhibited by the well-known consolidant tetraethoxysilane. Ca(OH)(2) and Sr(OH)(2) nanoparticles were prepared in laboratory and characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), dynamic light scattering (DLS), and Fourier transform infrared spectroscopy (FTIR). The kinetic stability of nanoparticles dispersions was determined by UV-vis spectrophotometric studies. Moreover, the study of the nanolime carbonatation process was carried out using FTIR spectroscopy. Distribution of the applied product into the stone substrate was examined by SEM-EDS. The chemical weathering effect of salt crystallization of the treated specimens was evaluated by performing the dry weight loss (DWL) test. All the results suggested that Ca(OH)(2) and Sr(OH)(2) nanoparticles, applied as 2-propanol dispersions, display some good properties as consolidating agents for a very porous bio-calcarenite such as Lecce stone

Evaluation of four sacrificial anti-graffiti polymers on a highly porous stone substrate

Anti-graffiti protection is becoming a common practice in many urban areas, because of increasing danger to buildings and monuments. The main aim of the present study was to evaluate the effectiveness of four commercially available polymeric materials on a very porous stone substrate against graffiti. Physical and chemical properties of the polymers were studied in order to select a class of products able to protect the surface from soiling and to reduce the impact of graffiti on the stone. Experiments were performed on specimens of a very porous bio-calcarenite (Lecce stone, LS), treated with microcrystalline wax (Bresciani, Italy), an emulsion of paraffin polymers (Art Shield-1, C.T.S., Italy), a fluoroelastomer in organic solvent (Fluoline HY, C.T.S.) and a fluoroelastomer in water emulsion (Tecnoflon TN Latex, Solvay Solexis, Italy). Surface properties of treated specimens were evaluated by performing chromatic and gloss variation measurements, optical microscope analysis, water capillary absorption and water vapour permeability tests. In order to examine the anti-graffiti behaviour, treated samples were soiled by a permanent marker and the surface properties studied again after the cleaning.  Colour changes were measured by determining the L*, a*, and b* coordinates of the CIELAB space. The overall chromatic changes (expressed as ΔE*) induced by treatments correspond to colour variations that cannot be detected by naked eye (ΔE* < 5), except for microcrystalline wax, which caused a higher variation (Figure). The most considerable gloss variations were observed on specimens treated with Latex TN and Art Shield-1. Water capillary absorption data indicated that water repellent behaviour of Latex TN was higher than the other polymers. The shielding effect exhibited by the other considered polymers was efficient only in the first few hours of contact with water and then it progressively decreased with increasing time. Water vapour permeability test indicated a considerable reduction of the vapour transmission rate only in the case of Latex TN. It should be noted that a low rate of vapour diffusion represents a drawback for surface treatments of stone.   The anti-graffiti effectiveness was evaluated by measuring colour changes on specimens after the staining/cleaning process. Variations of chromatic coordinates observed on the “cleaned” stones can be ascribed to traces of residual ink and directly correlated to the efficiency of anti-graffiti action. After cleaning of specimens treated with microcrystalline wax or Art-shield-1 very high ∆E* values (≥ 30) were obtained, indicating a poor protecting action of these products against graffiti. Fluorinated polymers exhibited more satisfactory anti-graffiti performance. In fact, after removing ink stains, ∆E* values determined on stone surface were 3 and 10 for Latex TN and Fluoline HY, respectively

Evaluation of four sacrificial anti-graffiti polymers on a highly porous stone substrate

Anti-graffiti protection is becoming a common practice in many urban areas, because of increasing danger to buildings and monuments. The main aim of the present study was to evaluate the effectiveness of four commercially available polymeric materials on a very porous stone substrate against graffiti. Physical and chemical properties of the polymers were studied in order to select a class of products able to protect the surface from soiling and to reduce the impact of graffiti on the stone. Experiments were performed on specimens of a very porous bio-calcarenite (Lecce stone, LS), treated with microcrystalline wax (Bresciani, Italy), an emulsion of paraffin polymers (Art Shield-1, CTS, Italy), a fluoroelastomer in organic solvent (Fluoline HY, CTS) and a fluoroelastomer in water emulsion (Tecnoflon TN Latex, Solvay Solexis, Italy). Surface properties of treated specimens were evaluated by performing chromatic and gloss variation measurements, optical microscope analysis, water capillary absorption and water vapour permeability tests. In order to examine the anti-graffiti behaviour, treated samples were soiled by a permanent marker and the surface properties studied again after the cleaning

Modification of shellac varnish by nanoparticles and a perfluoropolyether based polymer

Shellac has been widely used as a protective material for wooden furniture and musical instruments, due to its remarkable properties such as ease of application, high adhesion to the wood surface and protective properties along with its nonpoisonous nature. However, shellac varnishes have also some limitations such as softness of the coating, photodegradation, and sensitivity to alcoholic solvents and to pH variations. In the present study, de-waxed natural shellac (food quality shellac from Kremer-Pigmente) was selected and modified by introducing different inorganic nanoparticles as well as a fluorinated polymer. Silicates nanoparticles were added with the aim of improving the film hardness, while ZnO nanoparticles were expected to reduce photodegradation of the shellac matrix and finally, fluorinated polymer was considered with the aim of increasing chemical resistance and water repellent character of the resulting material. Four different shellac materials were prepared for these purposes by dispersing nanoparticles (silica, montmorillonite, zinc oxide) and perfluoropolyether in alcoholic solutions of shellac. Different experimental analyses were performed on both modified shellac films and maple wood specimens treated by brushing. Characteristics of modified shellac materials were investigated by performing hardness test, contact angle measurements, evaluation of chromatic variation after UV ageing, solubility and alkali resistance tests.  SEM-EDS analyses were also carried out on films and treated wood specimens.Quality and thickness of the coating are important parameters when products are developed for real case applications. Both native shellac and modified shellac treatments on wood specimens provided good quality coatings whose thickness was very close to real applications (about 25 µm, see Figure 1). Hardness measurements performed by international standard test indicated that the presence of silica or montmorillonite nanoparticles in shellac improves the hardness of the resulting coating. In addition, SiO2-shellac applied on wood specimens afforded an improvement of hydrophobic properties (see Figure 2), while Montmorillonite-shellac increased the base resistance property with respect to the native shellac.  ZnO-shellac treatment preserved almost unaltered the chromatic properties (L*, a* and b* coordinates of the CIELAB space) with respect to native shellac, even after UV ageing (750 h). Shellac modified by perfluoropolyether showed an improvement of hydrophobic behaviour and photo-stability after artificial ageing. Acknowledgement: The authors would like to acknowledge Dr. Claudio Canevari (Civica Scuola di Liuteria, Milan, Italy) for supplying different shellac batches, wood samples and also kind guidance for the research work

Improving the protective properties of Shellac-based varnishes by functionalized nanoparticles

Shellac is a natural varnish still known as one of the most elegant finishes for furniture and musical instruments, and currently used for restoration and refinishing of wooden antiques. However, it displays some limitations such as (i) sensitivity to alcoholic solvents (ii) softness of the coating, and (iii) considerable weathering due to photo-and bio-degradation. Hence, the main aim of this study was to improve the properties of shellac-based finish by introducing functionalized nanoparticles. Two inorganic nano-sized materials were considered: ZnO that was expected to reduce photo-and bio-degradation problems, and ZrO2 that was expected to improve the hardness of the varnish. Nanoparticles were synthesized and treated with a bifunctional silane coupling agent. Both plain and functionalized nanoparticles were extensively characterized using different experimental techniques. Functionalized nanoparticles were grafted on shellac through a reaction involving the epoxy-rings introduced on their surface. The resulting modified varnishes were applied on maple wood specimens according to traditional procedures. Different instrumental techniques and testing methods were used to characterize both nano-sized materials and the corresponding nanocomposites, as well as to evaluate the performance of the new coatings. The investigated composite materials display the same aesthetic appearance as plain shellac, while some other properties were improved. In particular, both nanocomposites are distinctly less soluble in alcohols than plain shellac and display antifungal properties. Moreover, coating containing functionalized ZnO nanoparticles displays photoprotection behavior, while shellac modified with ZrO2 nanoparticles exhibits a higher hardness when compared to the traditional varnish