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3D-Reflected-Light Microscopy as a Tool for Wood Identification in Historical Instruments


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This paper describes the technical approach and practical application of a new non-destructive microscopic identification method which is ideally suited for the wood identification of cultural (heritage) objects, e.g. music instruments. 3D-reflected-light microscopy enables the scientist to study individual components in historical instruments without destructive preparation of microscopic slides from detached wood blocks. This special technique offers a good option to determine which timbers are traditionally used for certain components in historical plucked and stringed instruments.
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3D-reflected-light microscopy as a tool for wood identification in
historical Instruments
Volker Haag1, Gerald Koch1, Valentina Zemke2, Sebastian Kirsch3, Sergej Kaschuro1,
1 Thünen Institute of Wood Research, Hamburg, Germany
2 Department of Wood Biology, Centre of Wood Research, University of Hamburg, Germany
3 Germanisches Nationalmuseum, Nürnberg, Germany
This paper describes the technical approach and practical application of a new non-destructive micro-
scopic identification method which is ideally suited for the wood identification of cultural (heritage)
objects, e.g. music instruments. 3D-reflected-light microscopy enables the scientist to study individual
components in historical instruments without destructive preparation of microscopic slides from de-
tached wood blocks. This special technique offers a good option to determine which timbers are tradi-
tionally used for certain components in historical plucked and stringed instruments.
1. Introduction
In the history of musical-instrument manufacture, traditional instrument builders often used
bequeathed” wood species for the individual components of the instrument which are char-
acterized by a specific texture and defined wood properties to produce a high sound quality.
Based on this experience passed down for generations, there is a considerable interest of
contemporary instrument builders to know which wood species the old masters like Torres
or Stradivarius have used. The standard non-destructive method for wood identification is
the macroscopic assessment of structural features. Regarding the results of a macroscopic
identification, they should be tentatively evaluated (Figure 1A). It is important to emphasize
that the possibilities of macroscopic wood identification are much more limited than those of
a microscopic study. Firstly, the number of characters available for observation is considera-
bly smaller. Secondly, in macroscopic identification one has to rely quite often on characters
subject to a high variability due to different growth conditions of the tree (viz. formation of
growth rings) or exposure to oxygen and UV radiation (viz. wood colour). This may lead to
subjective judgement on behalf of the user, and errors that might result in wrong decisions.
However, for identification of wood species in historical instruments, a microscopic examina-
tion is mostly impossible as such instruments are very valuable and no samples can be pre-
pared for microscopy. In practice, the use of macroscopic characters will probably end with a
choice of several likely matches whose safe separation must be left to microscopic analysis
(Figure 1B). For “official” or “judicable” wood identification, microscopic analyses are routine-
ly conducted. Using light microscopic techniques, up to 160 anatomical characters are availa-
ble which are internationally standardized and published in the IAWA lists of “Microscopic
Features for Hardwood and Softwood Identification” [1, 2]. The defined microscopic features
describe the individual characters of cell and tissue types, i.e., vessels, fibres, and ray as well
as axial parenchyma. Additional information is provided on mineral inclusions as part of a so
called “anatomical fingerprint”. Based on these requirements, the use of digital 3D reflected
light microscopy allows the microscopic observation of flat and uneven surfaces of solid
wooden components down to the smallest marquetry work without damaging individual
3D-reflected-light microscopy as a tool for wood identification in historical Instruments
Figure 1: (A) Soundhole-Inlays on macroscopic level (red box in Figure 1 A shows Figure 1 B) of a historical guitar
from Francisco Simplicio built in 1924. (right) Soundhole-Inlays on microscopic level.
2. Methods
As part of the STSM project "Non-destructive wood identification of historical Instruments
based on 3D-reflected-light microscopy", the scientists investigated eleven high value in-
struments of the Museu de la Música de Barcelona on a standard macroscopic level using
non-destructive tools (different kinds of hand lenses etc.) as well as digitized image micro-
scope analysis systems (CellF®, Olympus and KEYENCE® VHX-5000/ Figure 2 A+B) on the
microscopic level. For microscopic analysis close-up digital images were taken as well as rele-
vant histometrical data of the investigated instrument components. Images of anatomical
structures (Figure 4 and 5 A, B, C) and data (measurements etc.) were compared with infor-
mation available from computer-assisted wood identification systems (Commercial timbers,
macroHOLZdata and CITESwoodID) [3, 4, 5]. The microscopic features of the investigated
components of the different instruments were compared with vouchered reference speci-
mens of the scientific wood collection (Federal Research Institute for Rural Areas, Forestry
and Fisheries, Hamburg, Germany).
Figure 2: Microscopic investigation of a historical guitar with digitized image analysis system.
3. Results
The described methods for the macroscopic and microscopic wood identification were regu-
larly applied for each of the eleven selected instruments (year of construction between
approx. 1650 and 1950).
Volker Haag, Gerald Koch, Valentina Zemke, Sebastian Kirsch, Sergej Kaschuro,
Figure 4: Measurement of the average pit size (vertical) from a vessel element in wood of the neck (historic
guitar, Iganzio Fleta, 1953 /MDMB 1408).
Figure 5: The wood anatomy of Diospyros sp. (A), Dalbergia melanoxylon (B) and Juglans regia (C) A-C: Tangen-
tial section. Scale bars: A-C = 200 µm.
Systematic examination of the main components such as head, neck, back and sides as well
as the resonance board were carried out. Furthermore, small wooden components of the
mechanics, pegs, bridge, saddle, and decorative elements such as marquetry and inlays, e.g.,
in the case of a sound hole rosetta, were also analysed. The results of the studies reveal that
3D-reflected-light microscopy as a tool for wood identification in historical Instruments
the 3D-reflected-light microscopy mostly achieves the resolution of established transmitted
light microscopy for non-destructive wood identification. The technique allows the
differentiation of closely related species such as those belonging to the genera Swietenia and
Cedrela (MELIACEAE). Figure 4 shows a surface of the neck of a guitar (Ignazio Fleta, 1953)
with high microscopic magnification enabling the measurement of the average pit size. The
results revealed minute pits of about 2 μm which are typical for species of the genus
Swietenia. This excludes species of the genus Cedrela with a very similar colour and texture,
whereas pits are distinctly larger with values of approx. 5 - 7 μm. However, in some cases the
structural analysis of important sections is not possible due to constructive restrictions. For
example, the important transverse sections of framed fingerboards or marquetries are
inaccessible. In these cases, the analysis is restricted to the anatomical features on the
tangential and radial faces. Figure 5A shows the tangential section of a fingerboard from a
classical guitar of the 19th century. The image was taken with the 3D-reflected-light
microscope showing the anatomical structure of species of the botanical genus Diospyros spp.
= Black Ebony. Such structure can be clearly distinguished from those depicted in Figs. 5B
and 5C taken by “conventional” light microscopy and showing the tangential sections of the
“lookalike” timbers such as Dalbergia melanoxylon (African blackwood or grenadill) and
Juglans regia ( European walnut).
4. Conclusion
The present study shows that the technical approach of the 3D-reflected-light microscopy is
ideally suited for the non-destructive wood identification of cultural (heritage) objects, e.g.
musical instruments. Within the STSM project 120 individual components of eleven historical
instruments were analysed and identified.
The authors gratefully acknowledge the technical and scientific team of the Museu de la
Música de Barcelona who have prepared every instrument for this study. Thanks go especially
to Marisa Ruiz Magaldi, Esther Fernandez Cabrera, Sara Guasteví Olives, Manel Barcons Car-
bonell and Jaume Ayats Abeyà who have made these investigations possible.
[1] IAWA Committee 1989. IAWA List of microscopic features for hardwood identification
(ed. E.A. Wheeler, P. Baas, P.E. Gasson). IAWA Bull. n.s. 10(3): 219-332.
[2] Richter, H.G., D. Grosser, I. Heinz & P.E. Gasson (editors) 2004: IAWA list of microscopic
features for softwood identification (by an IAWA committee). IAWA Journal 25(1): 1-70.
[3] Richter, H.G., M. Oelker & G. Krämer (2002): macroHOLZdata Computer-gestützte
makroskopische Holzartenbestimmung sowie Informationen zu Eigenschaften und
Verwendung von Nutzhölzern. CD-ROM, Holzfachschule Bad Wildungen, Selbstverlag.
[4] Richter, H.G. & M. J. Dallwitz (2000 onwards). 'Commercial timbers: descriptions, illus-
trations, identification, and information retrieval.' In English, French, German, Portu-
guese and Spanish. Version: 4th May 2000.
[5] Richter, H.G., Gembruch, K. & G. Koch 2005: CITESwoodID Innovative medium for
education, information and identification of CITES protected trade timbers. CD-ROM.
Federal Agency for Nature Conservation (BfN) and Federal Research Centre for Forestry
and Forest Products (BFH), self-published.
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