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Wood science for conservation of cultural
heritage – Braga 2008
PROCEEDINGS OF THE INTERNATIONAL CONFERENCE
HELD BY COST ACTION IE0601 IN BRAGA (PORTUGAL)
5-7 NOVEMBER 2008
Edited by
ȱȱȱȱȱȱȱȮȱ ȱŘŖŖŞȱDZȱȱȱȱ ȱȱ ȱ ¢ȱ ȱ ȱ ŖŜŖŗȱ ǻȱ Ȭȱ ǰȱ śȬŝȱ ȱ ŘŖŖŞȱ Ȧȱ ȱ ¢ȱ ȱ ǯȱ Ȯȱ £ȱ DZȱ £ȱ¢ȱǰȱŘŖŗŖǯ ǻȱȱȱDzȱŜŝǼ DZȦȦǯǯȦşŝŞŞŞŜŚśřŗŜśŜ ȱȱşŝŞȬŞŞȬŜŚśřȬŗśŝȬŗȱǻǼ ȱȱşŝŞȬŞŞȬŜŚśřȬŗŜśȬŜȱǻǼ ȱȱȱȱȱȱ ŖŜŖŗȱȱȱ ǰȱ¢ȱ ȱ ȱ ȱ ȱ ȱ ȱ ȱ ȱ ȱ ȱ ȱ ¢ȱ ǯ ȱȱȱȱ£ȱȱȱ¢ȱǯȱȱǯȱǰȱ ȱ£ȱȱȱȱŘŖŖŞȱǰȱȱȱȱȱ ¢ȱȱ¢ȱǯȱ ȱ ǰȱȱȱȱǯȱȱȱȱ ȱȱȱȱǰȱȱȱ¢ȱ ǯ ȱȱȱȱȱ£ȱ¤£ ȚȱŘŖŗŖȱ£ȱ¢ȱ ¥ȱȱȱȱ£ £ȱ¢ȱ ȱ£ǰȱŘŞǰȱśŖŗŘŘȱ£ǰȱ ¢ DZȦȦ ǯǯȦ ȱȱ ¢
SUMMARY
Introduction ... 5 (A) MATERIAL PROPERTIES... 9
Sorption of moisture and dimensional change of wood species used in historic objects
Lukasz Bratasz*, Roman Kozlowski, Antonina Kozlowska, Bartosz Rachwal... 11
Vibrational properties of tropical woods with historical uses in musical instruments
Iris Brémaud1,2*, Pierre Cabrolier1,2, Kazuya Minato, Jean Gérard3, Bernard Thibaut4... 17
Creep properties of heat treated wood in radial direction
Julien Colmars1*, Takato Nakano2, Hiroyuki Yano3, Joseph Gril1... 24
Measurement of the elastic properties of minute samples of wood along the three material directions
Anh Tuan Dinh1,2*, Gilles Pilate3, Carole Assor1,2, Patrick Perré1,2... 30
Prediction of linear dimensional change of unrestricted wood at different levels of Equilibrium Moisture Content
Michael Formosa1,2 Martin Musumeci2... 36
Ageing of wood – described by the analyses of old beams
Michael Grabner*, Maria Kotlinova ... 42
Hygro-Lock integration in a Kelvin Voigt model
Jean Marie Husson, Frédéric Dubois*, Nicolas Sauvat, Octavian Pop ... 47
Research on the Aging of Wood in RISH
Shuichi Kawai*, Misao Yokoyama, Miyuki Matsuo, Junji Sugiyama... 52
Evaluation of the aging wood from cultural properties as compared with the accelerated aging treatment -Analysis on color properties-
Miyuki Matsuo1*, Misao Yokoyama1, Kenji Umemura1, Junji Sugiyama1, Shuichi Kawai1, Shigeru
Kubodera2, Takumi Mitsutani2, Hiromasa Ozaki3, Minoru Sakamoto3, Mineo Imamura3... 57
Strength and MOE of Poplar wood (Populus alba L.) across the grain: experimental data
Paola Mazzanti*, Luca Uzielli ... 62
Photodegradation and thermal degradation of outdoor wood
Laszlo Tolvaj1*, Sandor Molnar2... 67
(B) BIODETERIORATION... 73
Romanian Wooden Churches Wall Painting Biodeterioration
Livia Bucúa1*, Corneliu Bucúa2... 75
Disinfection and consolidation by irradiation of wooden samples from three Romanian churches
Mihalis Cutrubinis1*, Khôi Tran2, Eugen Bratu1, Loic Caillat2, Daniel Negut1, Gheorghe
Niculescu3... 81
Changes of mechanical and chemical properties of wood after brown-rot decay and blue staining Miha Humar, Bojan Buþar, Viljem Vek,, Franc Pohleven ... 88 Wood decay fungi in Latvian buildings including cultural monuments
Ilze Irbe*, Ingeborga Andersone... 94
Fungal decontamination by cold plasma: an innovating process for wood treatment
Charlotte Leclaire1*, Elodie Lecoq2, Geneviève Orial3, Franck Clement2, Faisl Bousta3... 101
Diagnosis of painted wood ceiling planks from an eighteen century building
Teresa Sande Lemos1*, Mafalda Sobral1, Lina Nunes1,2... 106
ȱ ȱǻȱ¢ǼǰȱȱȱȱȱȱȱȱȮȱŘŖŖŞDZȱȱȱȱ ȱ ȱȱ¢ȱȱȱ ŖŜŖŗȱǻȱȬȱǰȱśȬŝȱȱŘŖŖŞǰȱ ȱşŝŞȬŞŞȬŜŚśřȬŗśŝȬŗȱǻǼȱ ȱşŝŞȬŞŞȬŜŚśřȬŗŜśȬŜȱǻǼȱȚȱŘŖŗŖȱ£ȱ¢ȱ
SUMMARY
2
Studies on Insect Damages of Wooden Cultural Heritage in Latvia
Uwe Noldt1*, Guna Noldt2, Ingeborga Andersone3, Bruno Andersons3... 111
Termite infestation risk in Portuguese historic buildings
Lina Nunes* ... 117
Biodeterioration of Cultural Heritage in Estonia
Kalle Pilt* ... 123
Degradation of melanin and biocides by ligninolytic fungi
Franc Pohleven1*, Iztok Vidic1, ýrtomir Tavzes2... 129
Mould on organs and cultural heritage objects. Investigations in eight churches in Saxony
Wolfram Scheiding*, Katharina Plaschkies, Björn Weiß ... 135
Biological deterioration of historical wooden roof and floor structures and their renovation
Jelena Srpþiþ* ... 142 Orientated Investigation to kill the mycelia of the Dry Rot Fungus, Serpula lacrymans, with
microwaves
Merle Strätling1*, Wibke Unger2, Karin Petersen3... 148
Research study on the effects of the Thermo Lignum® Warmair treatment on art objects with paint and gilt finishes
Florian Tscherne*1, Bernhard Schachenhofer2, Karen Roux3... 153
(C) CHARACTERIZATION AND MEASUREMENT TECHNIQUES ... 159
Non destructive imaging for wood identification.
Junji Sugiyama*, Suyako Mizuno, Yoshiki Horikawa, Chiori Ito, Misao Yokoyama ... 161
Methods of non-destructive wood testing
Peter Niemz* ... 163
Measurement and simulation of dimensional changes due to flows of heat and moisture in wood and wood-based materials: How objects of cultural heritage can be studied by methods developed for industrial applications
Dr. Jochen Aderhold*, Dr. Hiltrud Brocke... 169
In the heart of the limba tree (Terminalia superba Engl. & Diels): detection methods for heart rot and false heartwood
Maaike De Ridder1,2*, Jan Van den Bulcke1, Hans Beeckman2, Joris Van Acker1... 175
Local deformation reactivity of Panel paintings in an environment with random microclimate variations: the Maltese Maestro Alberto's Nativity case-study
Paolo Dionisi-Vici1*, Michael Formosa2, J Schiro2, Luca Uzielli3... 180
Physical and mechanical characterization of ancient wooden musical instruments for conservation purposes
Marco Fioravanti1*, Paola Mazzanti1, Giacomo Goli1, Gabriele Rossi Rognoni2, Nicola Sodini1
... 186 NIR archaeometry as a powerful tool for investigating the archaeological wood - investigation of
thermal degradation mechanism of softwood and hardwood-
Tetsuya Inagaki*1, Katsuya Mitsui2, Satoru Tsuchikawa1... 192
NIR archaeometry as a powerful tool for investigating the archaeological wood - spectroscopic observation of the degradation process in thermally treated wood using a deuterium exchange method
Tetsuya Inagaki*, Satoru Tsuchikawa ... 196
NIR spectroscopic monitoring of water adsorption/desorption process in modern and archaeological wood
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Numerical Simulation of the Strength of Wooden Structures: Application to Historic Pianoforte
Michael Kaliske1*, Eckart Resch1, Jörg Schmidt2... 203
Simple Electronic Speckle Pattern Interferometer (ESPI) for the investigation of wooden art objects
Lukasz Lasyk, Michal Lukomski*, Lukasz Bratasz ... 209
Structural defect detection using acoustic holography in the cultural heritage field – A preliminary study
Sandie Le Conte1*, Sylvie Le Moyne2... 214
Experimental and numerical mechanical study of a framing technique for cupping control of painted panels combining crossbars and springs
Bertrand Marcon1,2, David Dureisseix1, Paolo Dionisi-Vici2, Joseph Gril1, Luca Uzielli2... 219
Effect of thermal treatment on structural defects of model panel paintings
Anna Moutsatsou1*, Eleni Kouloumpi1, Agni-Vasileia Terlixi1 , Marc Georges2, Cédric Thizy2,
Vici Tornari3 , Michail Doulgeridis1... 225
Inter-comparison of colour measurements of poly-chromed wooden objects which were irradiated for disinfection reasons
Constantin Daniel Negut1*, Laurent Cortella2, Mihalis Cutrubinis1, Khôi Tran2, Corneliu
Catalin Ponta1... 230
Characterization of waterlogged wood by infrared spectroscopy
Benedetto Pizzo1*, Ana Alves2, Nicola Macchioni1, Antonio Alves2, Gianna Giachi3, Manfred
Schwanninger4, José Rodrigues2... 236
Structure, mock-up model and environment-induced deformations of Italian laminated wood parade shields from the 16th century
Luca Uzielli1*, Elisa Cardinali1 , Paolo Dionisi-Vici1,2, Marco Fioravanti1, Nicola Salvioli3... 242
(D) CONSERVATION... 249
European Technical Committee 346 - Conservation of Cultural Property - Updating of the activity after a three year period
Vasco Fassina*... 251
The Wreck of Vrouw Maria - Current Situation and Future Perspectives
Eero Ehanti* ... 259
Romanian Architectural Wooden Cultural Heritage – The Present Status - a Survey
Bogdan Constantinescu*... 265
Ressurreição de Cristo – Panel from the XVI century, Museu de Arte Sacra da Sé de Évora. A repainted painting – dating and treatment (1974-2008)
Lília Maria Esteves*1, Raul Adalberto Leite2... 271
On 18th- and 19th- Century Sacristy Furniture in the Maltese Islands: Materials and Techniques
Michael Formosa* ... 274
Defibring of historical roof beam caused by ammonium sulphate and ammonium phosphates based fire retardants
Irena Kuþerová1*, Martina Ohlídalová2, JiĜí Frankl3, Michal Kloiber3, Alena Michalcová4... 281
Nossa Senhora do Rosário and Anjo Ceroferário. Examination and conservation of two different
wooden polychrome sculptures, at the IMC’s Department of Conservation
Elsa Murta1*, Diogo Sanches2... 287
The consequences of wooden structures consolidation through traditional techniques on the resistance of support panels and paint layers (Some case study - Stelea Monastery Targoviste, Humor Monastery and Arbore Monastery)
SUMMARY
4
(E) STRUCTURES... 295
What one needs to know for the assessment of timber structures Helena Cruz*, José Saporiti Machado, Pedro Palma ... 297
Experimental investigations on flexural strengthening of old wood members in historical buildings with GFRP Y. Batebi Motlagh¹*, Y. Gholipour²,Gh Ebrahimi³, M. Hosseinalibeygi4... 302
Structural behaviour of traditional mortise-and-tenon timber joints Artur O. Feio1*, Paulo B. Lourenço2, José S. Machado3... 309
Wooden Load Bearing Structural Elements of Kula Traditional Houses Case Study of Zabunlar and Göldeliler Houses Mine Tanac*, Ozgul Yõlmaz Karaman... 316
(F) OTHER CONTRIBUTIONS TO WOOD SCIENCE... 323
Investigation on the utilization of pomegranate wood for particleboard production Homayoun Soleymani Ashtiani1*, Abolfazl Kargarfard2... 325
Collapse reconditioning of Eucalyptus camaldulensis Dehn from Algeria (arboretum Bainem) Mansour.Tazrout1*, M.Tahar Abadlia1, Atika Oudia2... 330
Index of Authors... 330
Annexes ... 339
Annex 1: Facts about COST Action IE0601 ... 341
Annex 2: Final program of the conference... 346
PHYSICAL AND MECHANICAL CHARACTERIZATION OF ANCIENT WOODEN MUSICAL INSTRUMENTS FOR CONSERVATION PURPOSES
Marco Fioravanti1*, Paola Mazzanti1, Giacomo Goli1, Gabriele Rossi Rognoni2, Nicola Sodini1
1
DISTAF, University of Florence, Italy
2
DISAS, University of Florence, Italy Abstract
The conservation of ancient wooden musical instruments is a topic of interest both for wood technologists and conservators. In particular, the state of the wooden sound box is investigated. The climatic conditions of exhibition and performance rooms are monitored. Moreover, the state of tension when tuning is analyzed and both forces and deformations are measured. The results obtained constitute the first step to acquiring the know-how to further the mechanical behavior of instruments subjected to long term loading tests, such as creep and mechanosorption.
1. Introduction
Ancient musical instruments are objects of great value both as historical relics and as real musical instruments that have been played up to now. In order to preserve these precious objects, it is necessary to monitor and analyze the conditions of conservation that are largely dependent on the conservation of the sound box which, in stringed instruments, is typically made of wood.
The aim of this ongoing study is to understand the effects of the events that may occur during the daily life of musical instruments, which, due to their importance, are considered not only as musical instruments but also as components of cultural heritage.
Besides biological decay, wood ageing is determined by the effects of both moisture variation and mechanical stress, as well as the coupling effects determined by their interaction over time. A cyclic variation of environmental parameters (T, RH%) increases the creep of wood, and it has a direct effect on fracture, time dependent deformation and stress relaxation in wood.
In the wealth of studies on the characterization of the acoustic properties of wood, the effects of material elasticity and viscosity on sound speed transmission (or on damping) of wood have been clearly established. Few studies have focused on the measurements of the load applied on the soundboards as effects of the tensioning of the strings.
All of this research is an important source of knowledge, but it does not enable drawing any conclusions for establishing the real effects of using the instruments on their conservation.
The main issues that this study aims to address are the following:
- mechanosorption: does it actually and significantly occur as a consequence of performance (theoretically load is applied and the moisture content of the wood changes during concerts)?; - load condition: as consequences of load application two opposite phenomena are theoretically
possible: wood relaxation and string creep;
- moisture variation: the actual amount and level of moisture variation inside the wood of instruments during their ordinary life (including performances).
In particular this paper is centered on the analysis of: - climatic conditions of the exhibition and concert rooms; - tuning forces;
- elastic deformation due to tuning.
* E-mail: marco.fioravanti@unifi.it ȱ ȱǻȱ¢ǼǰȱȱȱȱȱȱȱȱȮȱŘŖŖŞDZȱȱȱȱ ȱ ȱȱ¢ȱȱȱ ŖŜŖŗȱǻȱȬȱǰȱśȬŝȱȱŘŖŖŞǰȱ ȱşŝŞȬŞŞȬŜŚśřȬŗśŝȬŗȱǻǼȱ ȱşŝŞȬŞŞȬŜŚśřȬŗŜśȬŜȱǻǼȱȚȱŘŖŗŖȱ£ȱ¢ȱ
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2. Materials and methods
Measurements have been performed on several instruments, but the main source of data comes from a conservation study on Paganini’s violin “Cannone” by G. Guarneri del Gesù, which is now property of the city of Genoa in Italy (fig. 1).
2.1. Monitoring temperature and relative humidity of the air
The first step to guarantee optimal conservation of the instrument is to monitor the climatic conditions to which the violin is subjected, both during the exhibition and the performance.
The violin is conserved inside a glass case (fig. 1) in which the temperature and the relative humidity of the air are monitored by two probes (Rotronic, Hygroclip): the first one is set on top of the case and the other one is on the bottom, in order to measure a possible vertical gradient.
A special device was designed to measure the relative humidity of the air and the temperature of the violin during the performance. A miniaturized probe (Sensirion SHT75) is set in the hole that fits the end button, too. An electronic board (tmote sky, Moteiv), set between the top and the chin rest, sends the collected data to a laptop by radio wave system.
Fig. 1: the violin, mounted on the frame in the exhibition case.
2.2. Monitoring the weight variation
Climatic variations, particularly RH variation, inside the case are responsible for the violin weight variation. In order to monitor it, the instrument is hung on a frame which is placed on the scale (ohaus, AV2102C) that is connected to a PC in order to continuously collect the weight data. The data are
saved in a txt file according to an acquisition rate of one reading every five minutes.
2.3. Measuring tuning forces
During the tuning, the strings produce a force that depends on the frequency, the length and the unit mass of the string itself. In order to measure force, a specific load cell was designed at DISTAF in cooperation with Deltatech. It is an exact copy of the bridge mounted on the “Cannone”. It is made of iron and is equipped with extensometers (fig. 2). This measuring bridge is able to measure the force produced by the strings according to two perpendicular axes, named Z and X. Along the X axis we measure the transversal force, that is the force that develops along the perpendicular directions to the main axes of the violin itself, and along the Z axes we measure the force orthogonal to the top. The
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accuracy is 1mV that is the equivalent of 0,018N. The data are collected by an electronic board, NI USB621, and sent to the PC to guarantee continuous acquisition.
Fig. 2: the equipped bridge mounted on the violin.
2.4. Measuring elastic deformation
The force produced during tuning induces a deformation of the violin. The immediate deformation, that is the elastic deformation, is measured by an optical 3D digitizing system. The measure is based on the interferometric principle, that is the 3D scanning of the instrument due to the intersection of two different light beams. It enables generating a perfect reproduction of the object and the measure of its deformation according to an accuracy of 20 ȝm. The scanning is made by ATOS III scanner and Geomagic Studio carries out the image elaboration, in cooperation with DigiLab (fig. 3).
Fig. 3: the 3D scanning of the violin.
3. Results and discussion
3.1. Monitoring climatic conditions and weight variations
Inside the conservation case the climatic conditions can be considered stable during the whole of 2007. The temperature varied from 21°C to 25°C during the whole year. The RH% usually moved about 57.5% for the whole year, except for the autumn when the RH decreased to 51%. As a consequence,
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the weight variations are small, approximately 0,5 g that is 0,1% of the violin weight. An interesting thing happened after concerts. Usually the performance room is drier than the exhibition case, that is why the violin loses weight, but, after being in the case again, it continued to lose weight notwithstanding the increased relative humidity of the air. It has been assumed that the influence of the climate inside the case was great. That is why it is necessary to measure the climatic conditions inside the sound chamber (the empty space between the two boards) during performances (fig.4).
15 17,5 20 22,5 25 27,5 30 32,5 35 37,5 40 42,5 45 47,5 50 1 3 .4 0 .4 8 1 5 .3 6 .0 0 1 7 .3 1 .1 2 1 9 .2 6 .2 4 Time RH%, T°C RH% T °C
The violin is out the box The violin is in the reharsal hall
Trabucco ricomincia a suonare (prove) nella sala prove, accordatura
The violin is in the performance room
Concert starts
Concert stops Encore
The violin is in its case
Fig. 4: climatic conditions inside the violin’s sound chamber during a performance.
The analysis of weight variation during a performance is shown in Fig. 5; the violin loses about 1 g during the concert itself because of the different climatic conditions (fig 4). After this extraordinary event, the required time to regain the original weight, which is considered the equilibrium weight, is about one month notwithstanding that the climatic conditions in the conservation case are constant (fig 5). 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 1 5 /1 2 /0 7 0 .0 0 1 6 /1 2 /0 7 0 .0 0 1 7 /1 2 /0 7 0 .0 0 1 8 /1 2 /0 7 0 .0 0 1 9 /1 2 /0 7 0 .0 0 2 0 /1 2 /0 7 0 .0 0 2 1 /1 2 /0 7 0 .0 0 2 2 /1 2 /0 7 0 .0 0 2 3 /1 2 /0 7 0 .0 0 2 4 /1 2 /0 7 0 .0 0 2 5 /1 2 /0 7 0 .0 0 2 6 /1 2 /0 7 0 .0 0 2 7 /1 2 /0 7 0 .0 0 2 8 /1 2 /0 7 0 .0 0 2 9 /1 2 /0 7 0 .0 0 3 0 /1 2 /0 7 0 .0 0 3 1 /1 2 /0 7 0 .0 0 1 /1 /0 8 0 .0 0 2 /1 /0 8 0 .0 0 3 /1 /0 8 0 .0 0 4 /1 /0 8 0 .0 0 5 /1 /0 8 0 .0 0 6 /1 /0 8 0 .0 0 7 /1 /0 8 0 .0 0 8 /1 /0 8 0 .0 0 9 /1 /0 8 0 .0 0 1 0 /1 /0 8 0 .0 0 1 1 /1 /0 8 0 .0 0 1 2 /1 /0 8 0 .0 0 1 3 /1 /0 8 0 .0 0 1 4 /1 /0 8 0 .0 0 1 5 /1 /0 8 0 .0 0 1 6 /1 /0 8 0 .0 0 1 7 /1 /0 8 0 .0 0 1 8 /1 /0 8 0 .0 0 1 9 /1 /0 8 0 .0 0 time RH%, T° 432 432,2 432,4 432,6 432,8 433 433,2 433,4 g. T° RH% Weight
Equilibrium violin weight before the concert 433,10 g.
Violin weight after the concert: 432,12 g.
Equilibrium weight reached
Fig. 5: time to regain the equilibrium weight after the concert.
3.2. Measuring tuning forces
CHARACTERIZATION OF ANCIENT WOODEN MUSICAL INSTRUMENTS FOR CONSERVATION PURPOSES 190 -20 -10 0 10 20 30 40 50 60 0 200 400 600 800 1000 1200 Time [s] F o rc e s [N ]
Bass bar side Soundpost side X
Fig. 6: forces shown during the tuning.
Looking at the Z axes we can see that on the soundpost side the forces, amounting to 50 N, are higher than the bass bar side (40 N). This is due to the different longitudinal tension necessary to tune the strings: the MI string is on the soundpost side and it is the one that needs greater force to be tuned. The gap between the two sides is 10 N, that is equivalent to 20% of the maximum force.
Analyzing the forces parallel to the top of the violin (X axes), we observe low values, around 4 N, when the violin is tuned. It means that the tuning stress according to that direction is negligible compared to the orthogonal forces (4,5% of the orthogonal forces).
3.3. Measuring elastic deformation
The results of the 3D scanning of the tuned violin (fig. 6 for the forces shown during measurement) show the deformation of the sound box, c cupid arch, and the high movement of the neck. Tuning produces a tension of the strings that is balanced by a deformation of the violin, that in simple terms consists of a compression of the top and a tension of the back. The neck is pulled up 1,335 mm by the action of the strings (the red zones in fig. 7a), and at the same time the fingerboard is pushed down 0,55 mm, which produces a rotation of the neck around its insertion point in the sound box.
The sound box is not deformed on the edges (the green zones in fig. 7a), but it shows a clear cupid arch deformation at the centre. In the bridge area the top is pushed down by the direct orthogonal forces expressed by the bridge itself (blue zone in fig. 7a). Near the end button and the fingerboard the top is obviously pulled up by the action of the tailpiece on one side, and the neck on the other, while the bridge acts as if it was a separating line.
The deformations are asymmetrical on the top, because of the presence of the soundpost and the bass bar on the opposite sides. Where the soundpost is present the deformation produced by the bridge stress is rather small (0,117 mm), because the soundpost itself produces a restraining force. As a consequence of this mechanism, the deformation of this side of the top, shown as convexities, is more evident far from the bridge (0,222 mm near the fingerboard and 0,257 mm near the tailpiece).
On the opposite side, the bass bar, set along the top, does not contrast the bridge stress (the deformation amounts to 0,457mm), but it makes the violin stiffer far from the bridge (0,181 mm near the fingerboard and 0,029 mm near the tailpiece).
Therefore the deformations are greater in the bridge area and smaller far from it.
On the back (fig. 7b), the neck and the end button area are pushed up by the strings (blue and light blue zones, fig. 7b) . The sound box shows no deformation, or very small deformations (green zones, fig. 7b) limited between +0,05 and -0,05 mm, except for the soundpost area (yellow and orange areas, fig. 7b) and the deformation amounts to 0,13 mm. In fact, the soundpost produces a localized transversal compression on the back. Whereas on the other side the presence of the bass bar, which is not attached to the back, does not transmit deformations to it.
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(a) (b)
Fig. 7: elastic deformation on the top (a) and the back (b) of the violin tuned up with a string set mounted on during the performances.
4. Conclusions
The work described herein is part of a more complex study on improving the conservation conditions of wooden musical instruments, particularly violins. Results obtained thus far relate both to the climatic conditions and mechanical stresses to which the violins are subjected during exhibition and performances.
4.1. Variation in climatic conditions related to weight variations
The climatic conditions inside the exhibition case are stable and the weight variation of the violin is limited.
The main variations, both in relation to environmental conditions and weight, relate to the performance.
Moving the instrument to a usually drier room for concerts, results in loss of weight (1g), which needs about a month to be regained. This weight variation suggests that the violin is not perfectly insulated because of the imperfect waterproofing of the varnish and the contribution of the inside of the sound box, which is raw.
4.2. Mechanical behaviour
The study of the elastic deformation shows the deformative behaviour of the violin which can be generalized as follows. The violin can be divided in two parts: the neck and the sound box. The neck is subjected to a rotation around its insertion point on the sound box. The sound box is subjected to compression of the top and to tension of the back, in simple terms. The marginal areas are not deformed, while the central part shows a cupid arch deformation.
This knowledge of the elastic deformation of the violin represents the first step towards furthering the mechanical behaviour of the instrument subjected to long term loading such as creep and mechanosorption.
References
1. Harris, N. (): A qualitative analysis of the relationship between longitudinal string vibration,arching shape and violin sound-Part 1. http://violin.uk.com: London.
2. Mc Lennan, J.E.(1980): The violin as a structure – A consideration of the static force in the instrument. CAS Newsletter. 34: 15-19.
