Abstract
Violin varnishes are known to affect both moisture absorption and vibrational properties of violin wood. However, traditional multi-layered varnish systems suffer from substantial wear as a result of intensive use, which calls for deeper understanding of the specific impact of individual layers. Using sophisticated in-situ neutron imaging and vibrational modal analysis, we show how wood sorption and vibrational behavior of tonewood depend on the build-up of the varnish system. The results demonstrate the protective effect of complete coatings and emphasize that strongly worn regions cannot accomplish the function as an effective moisture barrier, which might pose a risk for frequently played or aged string instruments. Furthermore, the build-up of the varnish system affects the vibrational properties of the tonewood, influencing its final sound quality. This delicate interplay should be considered both for the handling of antique and aged violins and for the production of modern high-quality instruments.
Highlights
Violin varnishes are known to affect both moisture absorption and vibrational properties of violin wood
Neutron imaging is known as a convenient technique to investigate moisture content changes and liquid water transport in wood[26,27,28,29] and its suitability to study the influence of coatings on the sorption dynamics has been demonstrated[30]
As an approximation to the worn or artificially aged varnish regions of violins, we examined the influence of the applied pretreatments independently of the final varnish systems
Summary
Violin varnishes are known to affect both moisture absorption and vibrational properties of violin wood. Taking these alterations of the varnish system and their imitation on modern violins into account, the contribution of individual varnish treatments to the impact of the coating system is of particular interest For this purpose, we have studied the influence of common traditional European varnish materials and coating build-ups on the sorption process of the underlying wood to understand how instruments react to changes in relative humidity. By using in-situ neutron imaging, we could non-destructively quantify and localize wood moisture gradient changes over time with a spatial resolution of several tens of micrometers (Fig. 1) For this purpose the impact of seven different coatings on the sorption process, ranging from simple pretreatments to complex varnish systems, was studied in comparison to unvarnished reference samples (Fig. 1c). The results reveal the relationship between the coating systems’ influence on the sorption and vibrational behavior, which must be expected and taken into account for violins
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