Aging of Wood for Musical Instruments: Analysis of Changes in Color, Surface Morphology, Chemical, and Physical-Acoustical Properties during UV and Thermal Exposure

Abstract

The acoustic features of old resonance wood in violins exhibit a superior quality when compared to those from new resonance wood. This study focuses on an assessment of the sound quality of two types of wood for musical instruments, spruce and maple (class A and D), before and after aging via thermal and UV exposure. The samples were characterized before and after UV aging in terms of color change (using a Chroma meter), surface morphology (using a MarSurf XT20 instrument), chemical changes (monitored by FTIR spectroscopy), and sound propagation speed (using an ultrasound device). After UV treatment, the wavier surface increased the area of exposure and degradation. Also, the color changes were found to be more accentuated in the case of spruce compared to sycamore maple. The FTIR results indicated more advanced aging processes for spruce when compared to maple under the same experimental conditions. This difference resulted mostly from the increased formation of carbonyl-containing chromophores via oxidative processes in spruce rather than in maple, which is in agreement with the color change findings. Exposure of both species to thermal and UV radiation led to an increase in sound propagation speed, both longitudinally and radially, and to a greater extent in wood quality class A when compared to quality class D.

Analysis of the Anisotropy of Sound Propagation Velocity in Thin Wooden Plates Using Lamb Waves

“…In spruce wood ( Picea abies Karst L.) in the longitudinal direction, tracheids constitute 90% of the wood volume and are approximately 100 times longer than they are wide, with them overlapping with adjacent cells both in the upper and lower parts by 20–30% of their length. This construction ensures the rapid propagation of waves in softwood [ 42 , 43 , 44 , 45 ]. In Figure 6 a,c, the microscopic view in the tangential direction of spruce wood in relation to the measurement principle can be noted.…”

“…In the case of maple wood ( Acer pseudoplatanus L.), the anatomical architecture is more complex than that of spruce wood, with it being made up of fibers, vessels, and axial parenchyma cells, with different shapes, organization, and quantity [ 42 , 43 ]. The vessels are small and rare, and the fibers occupy about 75% of the volume of the woody substance, the proportion of voids is 60% of the apparent volume, and from the point of view of organization, maple wood is part of the hardwoods with diffused, small pores, visible with a magnifying glass and quite rare, with their size and thickness decreasing towards the outer limit of the annual ring ( Figure 6 d–f) [ 44 , 45 ]. The vessels have average lengths between 350–800 μm, with small diameters, <50 μm.…”

Tunable Acoustic Properties Using Different Coating Systems on Resonance Spruce Wood

“…The color measurements were made in three points (see Figure S1, Supporting Information), selected to be representative of the natural nonuniformity of the wood color. [ 30–32 ] Color differences denoted ∆ E * between the total color of the control samples and the color values measured, in the same locations, after varnishing were determined with Equation : $$$$\begin{equation}{{\bf \Delta }}\ {E}^* = \sqrt {{{\left( {{{\Delta}}{L}^*} \right)}}^2 + {{\left( {{{\Delta}}{a}^*} \right)}}^2 + {{\left( {{{\Delta}}{b}^{\mathrm{*}}} \right)}}^2} \ \end{equation}$$$$where Δ L * is the lightness difference between the lightness after varnishing and the initial lightness, Δ a * is the difference in the redness between the value after varnishing and the initial value, and Δ b * is the difference in yellowness between the value recorded after varnishing and the initial value.…”

“…The value of the contact angle (denoted CA) depends on three factors: the morphology of the substrate expressed by the surface tension between the solid and gas medium (mN m −1 ); the nature of the liquid expressed by the superficial liquid and gas tension (mN m −1 ); the nature of liquid and substrate interactions expressed by the surface tension between the solid–liquid medium (mN m −1 ). [ 32,33 ] The CA was determined with the System OCA‐20 equipment, using successively distilled water and glycerin, for the drop, with a volume of 10 µL. Thus, the values of the contact angle for water (noted CAW) and for glycerin (CAG) were measured.…”

Identification of Damping of Spruce Wood (Picea abies) under Various Levels of Moisture Content Using Time-Scale Decomposition

“…Mania and Skrodzka [9] and Danihelova et al [10] investigated the effect of thermal modification on the damping of spruce wood, Stanciu et al [11] investigated the effect of ammonia treatment; and Buchelt et al [12] investigated the influence of thermal modification on damping and on the modulus of elasticity at different moisture contents. The damping properties of different tree species used for musical instruments were studied by Wegst [13], Merhar and Humar [14], Sproßmann et al [15], and Gurau et al [16]. Temperature also plays an important role in damping the vibrations of wood.…”