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Keywords:

  • compound middle lamella;
  • radiation ratio;
  • resonance wood;
  • resonance frequency;
  • violins;
  • wood decay fungi

Summary

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References
  • • 
    Violins produced by Antonio Stradivari during the late 17th and early 18th centuries are reputed to have superior tonal qualities. Dendrochronological studies show that Stradivari used Norway spruce that had grown mostly during the Maunder Minimum, a period of reduced solar activity when relatively low temperatures caused trees to lay down wood with narrow annual rings, resulting in a high modulus of elasticity and low density.
  • • 
    The main objective was to determine whether wood can be processed using selected decay fungi so that it becomes acoustically similar to the wood of trees that have grown in a cold climate (i.e. reduced density and unchanged modulus of elasticity).
  • • 
    This was investigated by incubating resonance wood specimens of Norway spruce (Picea abies) and sycamore (Acer pseudoplatanus) with fungal species that can reduce wood density, but lack the ability to degrade the compound middle lamellae, at least in the earlier stages of decay.
  • • 
    Microscopic assessment of the incubated specimens and measurement of five physical properties (density, modulus of elasticity, speed of sound, radiation ratio, and the damping factor) using resonance frequency revealed that in the wood of both species there was a reduction in density, accompanied by relatively little change in the speed of sound. Thus, radiation ratio was increased from ‘poor’ to ‘good’, on a par with ‘superior’ resonance wood grown in a cold climate.

Introduction

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

Instruments produced by Antonio Stradivari during the late 17th and early 18th centuries are reputed to have superior tonal qualities than more recent instruments. Dendrochronological studies show that, during his later decades, Stradivari used Norway spruce wood that had grown mostly during the Maunder Minimum (Burckle & Grissino-Mayer, 2003; Topham & McCormick, 2000), a period of reduced solar activity when relatively low temperatures caused trees to lay down wood with narrow annual rings, a high modulus of elasticity and low density (Esper et al., 2002).

Traditionally, wood used in the manufacture of musical instruments is treated with primers, varnishes or minerals to stiffen it. Such treatment can strengthen the adhesion between cell layers, but increases the density and vibrating mass because the cell lumina become occluded by the substance (Barlow et al., 1988; Schleske, 1998, 2002a), which ultimately reduces the speed of sound.

The increase in density has an adverse affect on the radiation ratio (R= speed of sound (c)/density (ρ)), reducing the speed of sound and its resonance frequencies (Barlow et al., 1988; Schleske, 2002b). Tests of other chemical treatments have shown that they increase the dynamic modulus of elasticity (EL and ER) and decrease the damping factor (δL and δR) (Yano et al., 1994; Ono & Norimoto, 1984; Meyer, 1995). Such treatments do not alter wood density, but increase the crystallinity of the cell wall, which is considered disadvantageous for wood processing (Yano et al., 1994). Other authors suggest that the wood of violins made by Guarneri and Stradivari was chemically treated to kill woodworm and fungi (Nagyvary et al., 2006).

An alternative approach to improving the acoustic properties of wood is to reduce its density by fungal or bacterial degradation. Some degradation probably resulted from the practice during the 17th and 18th centuries of floating tree trunks in water (Gug, 1991), but there is no evidence that this caused any noticeable reduction in wood density. According to Nagyvary (1988), the microbial degradation of pit membranes that occurred during this treatment would have resulted in an increase in wood permeability, so that subsequent penetration of varnish was enhanced. Recently, a new thermal treatment has been used to improve the acoustic properties of resonance wood. Treatment at high temperatures results in a reduction in density, because of decomposition of hemicellulose and cellulose, but the modulus of elasticity is reduced (Wagenführ et al., 2005a,b). A negative side-effect of the treatment is that the material becomes brittle, causing problems during the manufacture of instruments.

Most of the described treatments alter the woody cell wall and adversely affect the properties of the compound middle lamellae, both of which have a pivotal role in determining the overall stiffness of wood.

In a homogeneous bulk material, ignoring surface effects, the speed of sound, c, is governed by two mechanical properties: the modulus of elasticity and the density. In wood, which is strongly anisotropic, c varies directionally and is increased by any discontinuities in the compound middle lamella, such as those resulting from microbial degradation. Using the formulae shown in Table 1, it can be deduced that such degradation, even if very slight, results in an abrupt reduction in the E modulus and speed of sound (Schwarze et al., 1995) and has a negative impact on the acoustic properties of the wood.

Table 1.  Principal acoustic properties used for the assessment of tonal wood quality of axial (L) and radial (R) samples
PropertyAssessment
Density, ρ (kg m−3)ρ for the specimens in L and R directions
Young's modulus of elasticity, E (MPa)E for L and R directions
Speed of sound, c (m s−1)inline image for L and R directions
Radiation ratio, R (m4 kg−1 s−1)inline image for L and R directions
Damping factor, δL for L direction and δR for R directioninline image where fr is the resonance frequency, Δf the associated damping and K is a coefficient which varies between inline image and inline image

The compound middle lamella is penetrated or otherwise altered by most species of wood-decay fungi, except for members of the Xylariaceae (e.g. Kretzschmaria deusta and Xylaria longipes), which have little ability to degrade guaiacyl (Nilsson et al., 1989; Schwarze et al., 1995), which the compound middle lamella contains in very high concentrations. As a result, this layer remains as an intact skeleton, even at quite an advanced stage of decay (Nilsson et al., 1989; Schwarze et al., 1995; Schwarze, 2007), which explains why the speed of sound through the wood is little affected until that stage (Schwarze et al., 1995, Schwarze, 2007) and is the reason why decay caused by K. deusta is hard to detect in trees by means of acoustic devices (Schwarze et al., 1995, 2004; Schwarze, 2007).

The objective of this study was to investigate whether wood-decay fungi, such as the soft-rot fungus X. longipes, which lacks the ligninolytic ability to degrade the compound middle lamella, or the white-rot fungus Physisporinus vitreus, which does so only at an advanced stage of wood decay, can be used to improve the acoustic properties of resonance wood. For this purpose, wood specimens of Norway spruce and sycamore before and after incubation were assessed microscopically, mechanically and physically (Spycher et al., 2008).

Materials and Methods

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

We selected 80 specimens of the heartwood from Norway spruce (Picea abies L.) and 40 specimens from sycamore (Acer pseudoplatanus L.), free from visible defects or knots and with narrow annual rings according to the criteria for resonance wood. The density of the Norway spruce and sycamore wood specimens ranged from 360 to 490 kg m−3 and from 530 to 630 kg m−3, respectively.

To determine acoustic properties in the axial as well as the radial direction, 20 specimens in each sample were cut with their longest sides axially orientated (‘axial specimens’) and another 20 were cut with their longest sides radially orientated (‘radial specimens’). The dimensions of the axial specimens were 3 mm (tangential) × 25 mm (radial) × 150 mm (longitudinal), and those of the radial specimens were 3 mm (tangential) × 25 mm (longitudinal) × 100 mm (radial). Before every measurement, wood specimens were preconditioned at 23°C and 50% RH until a constant weight was reached (i.e. the moisture content (MC) of the specimens was 10.5 ± 0.5%). The mass losses with their corresponding standard deviations (SD) were also measured before and after incubation at 23°C and 50% RH. Additionally, 40 specimens of Norway spruce wood were impregnated with 1% malt solution, so that the MC above the fibre saturation point was reached (approx. 28%) before incubation with Physisporinus vitreus (Pers.: Fr.) P. Karst. (a basidiomycete) and Xylaria longipes Nitschke (an ascomycete). The incubation process was initiated according to European Standard EN 113 (European Committee for Standardization, 1997) with the aim of exposing the wood to a high inoculum of each fungus to facilitate colonization of the wood. The samples were incubated in the dark at 22°C and 70% RH.

Five physical properties were assessed before and after 6, 12 and 20 wk incubation with the fungi, using resonance frequency (Görlacher, 1984) measurements according to Spycher et al. (2008) (Table 1). Differences between values in percentage before and after incubation were estimated for each specimen, and the average of these variations and the corresponding SD were calculated from 10 or five specimens for Norway spruce and sycamore, respectively.

Bending strength (σr) was determined by three-point bending tests, whereby a central load was applied to specimens with a span (L) of 100 mm (German Standard DIN 52186; Deutsches Institut für Normung EV, 1978). The tests were carried out with a universal 100 kN bending test machine with a load rate of 2.5 mm min−1. The load was measured using a 1000 N force sensing device with a maximum error of 2% and a midspan deflection (w) with a maximal error of 1%. Two values were recorded: the maximum stress (σmax MPa) reached and the bending strength for each specimen (σr MPa), where the maximal deflection was wmax. Mean values and SD were calculated from 20 and 12 wood specimens of Norway spruce and sycamore, respectively. One-way analysis of variance (ANOVA) of the recorded values was performed, with respect to acoustic properties and bending strength, for all wood samples using SPSS software (Chicago, IL, USA) with the significance level set at P < 0.05.

For light microscopy, the incubated wood was cut into smaller blocks (10 × 5 × 5 mm), which were embedded, sectioned and stained according to the procedures of Schwarze & Fink (1998). The specimens, with transverse, radial and tangential faces exposed for examination, were fixed in 2% glutaraldehyde buffered at pH 7.2–7.4, dehydrated with acetone, embedded in a methacrylate medium and subsequently polymerized at 50°C. The embedded specimens were sectioned at approx. 2 and 3 µm using a rotary microtome (Leica® 2040 Supercut) fitted with a diamond knife. For general observation of wood anatomy, sections were stained for 12 h in safranine and then counterstained for 3 min in methylene blue and 30 min in auramine. To detect early stages of selective delignification, duplicate sections were also stained with safranine and astra blue (Srebotnik & Messner, 1994). Safranine stains lignin regardless of whether cellulose is present, whereas astra blue stains cellulose only in the absence of lignin.

Colour micrographs (Kodak EPY 64T) were taken with a Leitz Orthoplan microscope fitted with a Leitz-Vario-Orthomat camera system.

Results

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

Anatomy of Norway spruce wood

The wood of Norway spruce is very homogeneous in structure and consists primarily of longitudinal tracheids (95%; Fig. 1a, b), generally with uniseriate bordered pits. Resin canals are surrounded by a sheath of eight to 12 or more thick-walled epithelial cells. Xylem rays are heterocellular (i.e. possess ray parenchyma and ray tracheids), with smooth walls. The transition from early wood to late wood is gradual.

image

Figure 1. Transverse sections (TS) of untreated controls and Norway spruce (Picea abies) wood incubated with Physisporinus vitreus. Late- (a) and early-wood (b) tracheids of control specimens. L, cell lumen; Sw, secondary wall; Cml, compound middle lamella. (c) After 12 wk incubation, preferential degradation of bordered pits (large arrow) and delignification of secondary walls (arrowheads) commence from hyphae (small arrows) growing within the cell lumen of the late- and early-wood tracheids. Note the hyphae (arrows) in the cell lumina growing on the S3 layer. Section stained with safranine, methylene blue and auramin. (d) Panel (c) stained with safranine and astra blue. Note that delignified regions of cell wall appear blue in close proximity to hyphae (arrows). (e) After 20 wk incubation, secondary walls are strongly delignified (arrowheads) and cell wall thinning is apparent in the late- and early-wood tracheids (f).

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Anatomy of sycamore wood

Sycamore wood, which is diffusely porous, contains groups of fibres that appear to be of high and low density when viewed in transverse section (Fig. 2a). The less dense groups lie between vessels and have abundant intercellular spaces. The denser groups are associated with the vessels, and each group forms a complete paratracheal sheath without intercellular spaces. Living wood fibres are also concentrated at the borders of the annual increments, where they are associated with apotracheal terminal parenchyma.

image

Figure 2. (a) Transverse sections (TS) of untreated sycamore (Acer pseudoplatanus) wood showing the diffuse porous distribution of vessels (v). Note the groups of fibres that appear to be of high and low density (arrows). V, vessels; Xr, xylem rays. (b) TS of sycamore wood incubated with Xylaria longipes. After 18 wk, fibre regions in between vessels (arrows) containing intercellular spaces (IZH) are preferentially degraded, whereas fibre regions without intercellular spaces (IZF) surrounding vessels are resistant to decay. (c–e) TS showing progressive cell wall thinning of wood fibre regions containing intercellular spaces (IZH) by Xylaria longipes after 6 (c), 12 (d) and 20 wk (e).

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Wood colonization and cell wall degradation

In the wood of Norway spruce incubated with P. vitreus, the main avenues of hyphal growth in the xylem were along the xylem rays and tracheids. After 6 wk incubation, the only detectable effect on the tracheids was selective degradation of pit membranes (Fig. 1c).

After 12 wk, degradation of the uniseriate xylem rays and selective delignification of the tracheid cell walls were apparent within the early wood. Initially, selective delignification was more pronounced in the xylem rays and the early wood, but at a more advanced stage of decay the late-wood tracheids were also affected. Delignification of the secondary walls of tracheids commenced from within the lumen towards the middle lamella and occurred in the immediate vicinity of the hyphae growing on the surface of the cell lumen (Fig. 1c). Cell wall delignification was more pronounced in the tangential direction and after staining with safranine, methylene and auramine staining resulted in a distinct colour change of the inner secondary wall from light to dark blue, indicating selective delignification and the exposure of cellulose. Confirmation was also obtained by staining sections with safranine and astra blue, which showed that the discoloured inner secondary wall was delignified and, in the absence of lignin, cellulose was subsequently stained blue (Fig. 1d).

In comparison with control sections (Fig. 1a,b), delignification was apparent in the late-wood tracheids after 12 wk incubation (Fig. 1c,d), followed by cell wall thinning that developed around hyphae in the cell lumina and progressed throughout the inner secondary wall. The compound middle lamella was not visibly altered, however, and remained intact even after 12 wk (Fig. 1c,d). After 20 wk incubation, attack of the compound middle lamella, which is the critical phase of degradation in the present context, commenced in the early wood (Fig. 1f), despite being absent in the late wood (Fig. 1e).

In the wood of sycamore incubated with X. longipes, hyphae (1–2 µm in diameter) were apparent within the cell lumina of fibres, vessels and parenchymal cells of the xylem rays. Hyphal growth was most abundant in the cell lumina of fibres with intercellular spaces (Fig. 2b–f). When viewed at low magnification, the preferential degradation of low-density regions produced a distinctive pattern (Fig. 2b), initially in the immediate vicinity of individual hyphae (Fig. 2c–e). In the early stages of decay, there was general dissolution of the cell walls, typical of a simultaneous rot, so that hyphae in the cell lumina induced a general thinning of the walls. At this time, there was no evidence of wall thinning within fibre regions without intercellular spaces, even though hyphae were present within their cell lumina (Fig. 2c–e). Even after 20 wk incubation, when the decay of the low-density fibre regions was more advanced, the compound middle lamellae and the walls of xylem rays and vessels were resistant to degradation (Fig. 2e). At this time, cell wall thinning commenced within fibre regions without intercellular spaces (Fig. 2e).

Alteration of the acoustic properties of degraded wood

Degradation of Norway spruce wood by P. vitreus was accompanied by changes in its acoustic properties (Fig. 3a,b). A significant increase (P < 0.05) in R was recorded after 12 and 20 wk incubation (Table 2) and can be attributed to a reduction in density (–14.8% after 20 wk), coupled with little change in the speed of sound (–2.7% after 20 wk). After 20 wk incubation, there was a significant increase (P < 0.05) in the damping factor (340% in the radial direction) (Fig. 3a,b), which correlated with the selective degradation of pit membranes.

image

Figure 3. Alterations in density and the acoustic properties of E modulus, speed of sound, radiation ratio (left axis) and damping factor (right axis) in Norway spruce (Picea abies) wood after incubation with Physisporinus vitreus. (a) Axial direction, (b) radial direction. Error bars ± SD. Significant differences between untreated controls and incubated samples: *, P < 0.05.

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Table 2.  Radiation ratio (± SD) in the axial direction in sycamore (Acer pseudoplatanus) and Norway spruce (Picea abies) wood specimens after 6, 12 and 20 wk incubation with Physisporinus vitreus and Xylaria longipes, respectively
Incubation periodSycamoreNorway spruce
Before incubationAfter incubation with X. longipesBefore incubationAfter incubation with P. vitreus
6 wk6.0 ± 0.56.4 ± 0.612.3 ± 1.312.3 ± 1.3
12 wk6.3 ± 0.77.0 ± 0.712.8 ± 0.813.7 ± 0.9
20 wk5.9 ± 0.46.8 ± 0.512.0 ± 0.313.7 ± 0.8

In sycamore wood that was incubated by X. longipes, throughout all incubation periods the speed of sound in the axial direction remained more or less the same as in the controls (Fig. 4a,b). By contrast, density was reduced by approx. 10% within 6 wk (Fig. 4a,b) and the R values increased significantly (P < 0.05; Table 2) after 6, 12 and 20 wk (Fig. 4a,b). No major alterations of the damping factor were recorded in the axial direction, which indicates that the damping capacity of the incubated sycamore wood resembled that of untreated wood.

image

Figure 4. Alterations in density and the acoustic properties of E modulus, speed of sound, radiation ratio (left axis) and damping factor (right axis) in sycamore (Acer pseudoplatanus) wood after incubation with Xylaria longipes. (a) Axial direction, (b) radial direction. Error bars ± SD. Significant differences between untreated controls and incubated samples: *, P < 0.05.

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Alteration of the strength of degraded wood

The axial bending strength of control specimens of Norway spruce was 75.8 ± 7 MPa, whereas specimens incubated for 20 wk showed values of 63.6 ± 10 MPa (Fig. 5). The radial bending strength of control specimens was 6.4 ± 0.5 MPa, whereas specimens incubated for 20 wk showed values of 4.7 ± 1 MPa (Fig. 5). The mean axial bending strength of the sycamore wood specimens incubated for 20 wk was 47.4 ± 6.6 MPa, compared with 68.8 ± 11.8 MPa in the controls (Fig. 5). The corresponding values for radial bending strength were 10.4 ± 2.2 MPa and 16.6 ± 1.2 MPa.

image

Figure 5. Bending strength (in MPa) of Norway spruce (Picea abies) and sycamore (Acer pseudoplatanus) wood incubated for 20 wk with Physisporinus vitreus and Xylaria longipes, respectively. Error bars ± SD. Significant differences between untreated controls and incubated samples: *, P < 0.05.

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Discussion

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

Incubation of wood with two species of decay fungi caused marked density losses and cell wall thinning; that is, the partly degraded wood resembled superior resonance wood grown under cold climate conditions. This finding is in good agreement with other research that shows that the gradual decomposition and loss of hemicellulose with time lowers wood density without affecting its Young's modulus, subsequently increasing the radiation ratio (Bucur, 2006).

The observed pattern of degradation by P. vitreus seems to be unique with regard to the selective delignification of the secondary wall without degradation of the middle lamellae, even at advanced stages of decay. The significant increase (P < 0.05) in the damping factor (340% in the radial direction) that was recorded after incubation of 20 wk can be attributed partly to selective degradation of pit membranes (Schwarze & Landmesser, 2000; Schwarze et al., 2006; Schwarze, 2007). The degradation of pit membranes by P. vitreus is an important aspect that could have significant benefits in wood protection processes, namely for improving the permeability of waterborne wood preservatives (Schwarze et al., 2006). Similarly, an increase in wood permeability facilitates penetration of varnish, which is traditionally used to increase the stiffness (i.e. Young's modulus of elasticity) of the wood used for making violins (Nagyvary, 1988). Thus, it is conceivable that the significant reduction in Young's modulus of elasticity recorded in Norway spruce wood incubated by P. vitreus could be mitigated by additional treatment with wood-stiffening varnishes (e.g. copaiba balsam), which can result in an increase in the speed of sound by 18.8% in treated compared with untreated wood (Schleske, 1998). Such treatment would ultimately further enhance the radiation ratio. Incubation with P. vitreus for > 20 wk will adversely affect the properties of resonance wood, rendering it unsuitable for violin manufacturing.

In sycamore wood incubated with X. longipes, degradation began preferentially within groups of libriform wood fibres containing intercellular spaces, leaving fibre regions without such spaces, vessels and xylem ray parenchyma undegraded and largely intact, even when decay had become advanced elsewhere. These differences in cellular decay resistance have been previously reported for Armillaria mellea on sycamore wood and correspond to the degree of lignification within the two types of fibre (Campbell, 1931, 1932; Nilsson et al., 1989; Schwarze et al., 2000; Schwarze, 2007). Even after 20 wk incubation, the compound middle lamella in sycamore wood showed little signs of degradation, which indicates that even longer incubation periods could be used without reducing the speed of sound.

Particularly in the case of the top plates for violins, a large R (Table 1) of the material is desirable to produce a big sound (Holz, 1966; Wegst, 2006; Spycher et al., 2008). A high radiation ratio in the axial direction is of utmost significance for first-quality resonance wood (Ono & Norimoto, 1983; Müller, 1986). For the manufacture of an excellent concert violin for use by a soloist, the violin maker requires at least ‘very good’ material quality for the two quarter cuts (top plate: Norway spruce wood; bottom plate: sycamore wood). In the present study, degradation of Norway spruce and sycamore wood by P. vitreus and X. longipes, respectively, was accompanied by significant increases (P < 0.05) in R after 6, 12 and 20 wk incubation (Table 2). In the wood of both species, improvement in the radiation ratio was achieved by a reduction in density of approx. 12%, coupled with relatively little alteration in the speed of sound (Table 2). In Norway spruce wood, R values of 10 and 16 have been measured in acoustically ‘poor’ and ‘excellent’ specimens, respectively, with corresponding values of 5.5 and 8 in sycamore wood (M. Schleske, unpublished). Thus, in our study, the acoustic quality of Norway spruce and sycamore wood was increased from ‘poor’ to ‘good’.

The axial bending strength of incubated Norway spruce and sycamore wood specimens was not significantly reduced, in comparison with the controls, after 20 wk incubation, whereas a significant reduction (P < 0.05; Fig. 5) in the radial bending strength of both wood species was recorded. These results are in good agreement with those of previous studies that showed that, in comparison with controls, the impact-bending strength of Norway spruce wood was not significantly reduced after 12 wk incubation with P. vitreus (Schwarze et al., 2006).

The reduction in radial bending strength is important for Norway spruce, but may not be relevant for the use of sycamore wood in violin-making (M. Schleske, unpublished); that is, the mechanical impact on the sycamore bottom plate is mostly a dynamic effect, while the static forces exerted in compression are compensated by the geometry of the violin (Bond, 1976; Spycher, 2008). Furthermore, the top plate made of Norway spruce wood is responsible for the global sound emission of the violin, but not for its strength and stability. The potentially disadvantageous radial strength losses in Norway spruce and sycamore wood after incubation could be mitigated simply by using thicker top and bottom plates (Wegst, 2006; Spycher, 2008).

The quality of the resonance wood is very important for the acoustic quality of the violin. The procedure described here for modifying wood is intended primarily to enable the manufacture of better solo instruments. A solo violinist prefers an instrument that can play ‘against’ the orchestra. Its tonal properties include high projection, high volume and dynamic range, together with a sensitive modulation of tonal colours, and these depend directly on the material quality of the resonance plates of the violin, which in turn is correlated positively with the velocity of the longitudinal sound waves (both across and along the grain) and negatively with wood density. A material with a high ratio of the speed of sound to density increases the sound emission of the instrument, which means that the plate amplitudes are high in relation to the force that excites the strings. This enhancement of resonance makes the difference between a violin of average quality and one that is suitable for a top soloist. Because of the enormous size of modern concert halls, acoustic instruments made from wood modified by fungi will be desirable for meeting the needs of soloists in the future.

In further studies, we will be attempting to optimize the uniformity of colonization and decay processes, particularly identifying the critical incubation time above which the radiation ratio is adversely affected. The exact influence of the bending strength on the violin will also be determined, using a prototype violin made from fungal-treated wood plates. Additionally, the influence of the damping factor on the acoustic quality of resonance wood and the effects of its modification on the final properties of the violin will be investigated.

Acknowledgements

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

We thank Michael Strässle from the Wood laboratory (EMPA) for his support during the bending strength tests, as well as Dr René Steiger and Martin Schleske, Meisteratelier für Geigenbau, for their helpful comments. Many thanks also to Karin Waldmann from the Professur für Forstbotanik (University of Freiburg) for making the microscopic sections, and to Dr David Lonsdale for his assistance with this paper.

References

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References
  • Barlow CY, Edwards PP, Millward GR, Raphael RA, Rubio DJ. 1988. Wood treatment used in Cremonese instruments. Nature 332: 313.
  • Bond CW. 1976. Wood anatomy in relation to violin tone. Journal of the Institute of Wood Science 7: 2226.
  • Bucur V. 2006. Acoustics of wood, 2nd edn . Berlin, Germany: Springer Series in Wood Science Springer.
  • Burckle L, Grissino-Mayer HD. 2003. Stradivaris, violins, tree rings, and the Maunder Minimum: a hypothesis. Dendrochronologia 21: 4145.
  • Campbell WG. 1931. The chemistry of white rots of wood. II. The effect on wood substance of Armillaria mellea (Vahl) Fr., Polyporus hispidus (Bull.) Fr. and Stereum hirsutum Fr. Biochemistry Journal 25: 20232097.
  • Campbell WG. 1932. The chemistry of white rots of wood. III. The effect on Wood substance of Ganoderma lipsiense (Pers.) Pat., Fomes fomentarius (Linn) Fr., Polyporus adustus (Willd.) Fr., Pleurotus osteratus (Jacq.) Fr., Armillaria mellea (Vahl) Fr., Trametes pini (Brot.) Fr. and Polystictus abietinus (Dicks.) Fr. Biochemistry Journal 26: 18271838.
  • Esper J, Cook ER, Schweingruber FH. 2002. Low-frequency signals in long tree-ring chronologies for reconstructing past temperature variability. Science 295: 22502252.
  • European Committee for Standardization. 1997. European Standard EN 113. Wood preservatives: test method for determining the protective effectiveness against wood destroying basidiomycetes. Determination of toxic values. Brussels, Belgium: European Committee for Standardization.
  • Deutsches Institut für Normung EV. 1978. German standard DIN 52186. Testing of wood: bending test. Berlin, Germany: Beuth Verlag.
  • Görlacher R. 1984. Ein neues Messverfahren zur Bestimmung des Elastizitätsmoduls von Holz. Holz als Roh- und Werkstoff 42: 219222.
  • Gug R. 1991. Choosing resonance wood. The Strad 102: 6064.
  • Holz D. 1966. Untersuchungen an Resonanzhölzern. 1. Mitteilung: Beurteilung von Fichtenresonanzhölzern auf der Grundlage der Rohdichteverteilung und der Jahrringbreite. Archiv für Forstwesen 15: 12871300
  • Meyer HG. 1995. A practical approach to the choice of tone wood for the instruments of the violin family. Catgut Acoustical Society Journal 2: 913.
  • Müller HA. 1986. How violin makers choose wood and what this procedure means from a physical point of view. In: HutchinsCM, ed. Research Papers in Violin Acoustics: 1975–1993, volume 1. Woodbury, NY, USA: Acoustical Society of America, paper 92.
  • Nagyvary J. 1988. Chemistry of Stradivarius. Chemical and Engineering News 66: 2431.
  • Nagyvary J, DiVerdi JA, Owen NL, Tolley HD. 2006. Wood used by Stradivari and Guarneri. Nature 444: 565.
  • Nilsson T, Daniel G, Kirk K, Obst JR. 1989. Chemistry and microscopy of wood decay by some higher Ascomycetes. Holzforschung 43: 1118.
  • Ono T, Norimoto M. 1983. Study on Young's modulus and internal friction of wood in relation to the evaluation of wood for musical instruments. Japan Journal of Applied Physics 22: 611614.
  • Ono T, Norimoto M. 1984. On physical criteria for the selection of wood for soundboards of musical instruments. Rheol Acta 23: 652656
  • Schleske M. 1998. On the acoustical properties of violin varnish. Catgut Acoustical Society Journal 3: 1524.
  • Schleske M. 2002a. Empirical tools in contemporary violin making: Part I. Analysis of design, materials, varnish and normal modes. Catgut Acoustical Society Journal 4: 5064.
  • Schleske M. 2002b. Empirical tools in contemporary violin making: Part II: psychoacoustic analysis and use of acoustical tools. Catgut Acoustical Society Journal 4: 8392.
  • Schwarze FWMR. 2007. Wood decay under the microscope. Fungal Biology Reviews 1: 133170.
  • Schwarze FWMR, Baum S, Fink S. 2000. Resistance of fibre regions in wood of Acer pseudoplatanus degraded by Armillaria mellea. Mycological Research 104: 126132.
  • Schwarze FWMR, Engels J, Mattheck C. 2004. Fungal strategies of wood decay in trees. Heidelberg, Germany: Springer.
  • Schwarze FWMR, Fink S. 1998. Host and cell type affect the mode of degradation by Meripilus giganteus. New Phytologist 139: 721731.
  • Schwarze FWMR, Landmesser H. 2000. Preferential degradation of pit membranes within tracheids by the basidiomycete Physisporinus vitreus. Holzforschung 54: 461462.
  • Schwarze FWMR, Landmesser H, Zgraggen B, Heeb M. 2006. Permeability changes in heartwood of Abies alba and Picea abies induced by incubation with Physisporinus vitreus. Holzforschung 60: 450454.
  • Schwarze FWMR, Lonsdale D, Mattheck C. 1995. Detectability of wood decay caused by Ustulina deusta in comparison with other tree-decay fungi. European Journal of Forest Pathology 25: 327341.
  • Spycher M. 2008. The application of wood decay fungi to improve the acoustic properties of resonace wood for violins. PhD thesis. Freiburg, Germany: Albert-Ludwigs-Universität Freiburg.
  • Spycher M, Schwarze FWMR, Steiger R. 2008. Assessment of resonance wood quality by comparing the physical and histological properties. Wood Science and Technology 42: 325342.
  • Srebotnik E, Messner K. 1994. A simple method that uses differential staining and light microscopy to assess the selectivity of wood delignification by white rot fungi. Applied Environmental Microbiology 60: 13831386.
  • Topham TJ, McCormick MD. 2000. A dendrochronological investigation of stringed instruments of the Cremonese School (1666–1757) including ‘The Messiah’ violin attributed to Antonio Stradivari. Journal of Archaeological Science 27: 183192.
  • Wagenführ A, Pfriem A, Eichelberger K. 2005a. Der Einfluss einer thermischen Modifikation von Holz auf im Musikintrumentenbau relevante Eigenschaften. Teil I: spezielle anatomische und physikalische eigenschaften. Holztechnologie 46: 3642.
  • Wagenführ A, Pfriem A, Eichelberger K. 2005b. Der Einfluss einer thermischen Modifikation von Holz auf im Musikinstrumentenbau relevante Eigenschaften. Teil 2: technologische eigenschaften, herstellung und prüfung von musikinstrumentenbauteilen. Holztechnologie 47: 3943.
  • Wegst UGK. 2006. Wood for sound. American Journal of Botany 93: 14391448.
  • Yano H, Kajita H, Minato K. 1994. Chemical treatment of wood for musical instruments. Journal of the Acoustical Society of America 96: 33803391.