The dendrochronological analysis of a stringed instrument requires inspecting the top plate, measuring the tree ring widths, establishing the chronology of the instrument, and dating through determining the end date-the year of the formation of the most recent tree ring.
Dendrochronology, the science of dating tree rings in the wood, defines in which calendar year a particular tree ring was formed. The method can be used to determine the age and authentication of wooden musical instruments. We present a protocol describing how to perform a dendrochronological analysis on stringed instruments and how to interpret the dating. The protocol describes the basic steps in the analysis of top plates, which are usually made of Norway spruce (Picea abies) or, more rarely, silver fir (Abies alba). First, the top plate is carefully inspected, and then the tree ring widths are measured directly on the instrument using high-resolution images. After completing the measurements, a tree ring sequence of the instrument is created, and, in the next step, dating is performed with a number of reference chronologies of the tree species from different geographical areas and instruments. The specialists who date the instruments also invest work in creating reference chronologies. The dendrochronological report provides the dating of an instrument as a calendar year (end date), indicating the year in which the last (most recent) tree ring on the top plate was formed when the tree was still alive. The end date represents the terminus post quem, the year after which the instrument was made or before which it could not have been made. To estimate the year of manufacture, one must consider the time required for wood drying and storing and the number of tree rings removed during wood processing. This protocol is intended to help those commissioning such an analysis to better understand how the analysis is performed and how to interpret the dendrochronological reports in terms of the age, origin, maker, and authenticity of the instrument.
The goal of this study is to present a protocol for the dendrochronological analysis of tree rings on the top plate of a wooden musical stringed instrument. Dendrochronology is used as a method to determine the age of the wood of the instrument by determining the year in which the youngest tree ring on the plate was formed and after which the instrument was made (or before which the instrument could not have been made).
Dating a musical instrument (such as a violin) is an important step in its authentication1,2,3,4,5,6. It is a complex process that involves the year in which the instrument was made, as well as the maker or instrument-making school or geographical area. To do this, dendrochronology is often combined with other techniques, which include the study of the label on the instrument (which is often not reliable) and the inspection of the instrument and its parts such as the outlines, scroll, wood figure and aging, varnish, f-holes, and purfling (Figure 1). The authentication can only be done by experts5,6,7.
Figure 1: The top of the violin and its parts. The wood of the top plate (also called the front plate, belly, or soundboard) made of Norway spruce (Picea abies) can be dated by dendrochronology. The characteristics and dimensions of other parts such as the scroll, f-holes, and purfling are studied by organologists and help to authenticate the instrument. Scale = 20 cm. Please click here to view a larger version of this figure.
Dendrochronology is the science of dating tree rings in the wood, also called annual rings, growth rings, or growth layers, which are formed every year in the trees of temperate zones. Dendrochronology clarifies in which calendar year a particular tree ring was formed. By dating the outermost and most recently formed tree ring just below the bark, the last year of a tree's life before it was cut down can be determined.
Dendrochronology is based on the principle that annual variations in tree ring width (and other characteristics) are largely influenced by the environment, especially the climate, in which the trees grow. When conditions are similar over an area, trees of the same species show similar tree ring variations from year to year8. This means that the tree ring series (i.e., the temporal sequence of tree ring widths over time) is similar for trees of the same species in the same area.
The dating of wooden instruments follows the principles used for dating historical objects. In most cases, it is based on measuring tree ring width, creating tree ring series of the same object, cross-dating (to determine their matching position), and averaging them into a floating chronology of an object showing the tree ring series in relative time3,4,6.
Absolute dating (determining the calendar year of tree ring formation) is accomplished by cross-dating with one or more reference chronologies established for a particular tree species and geographic area4,6. The reference chronologies must be based on the tree ring widths of a sufficient number of trees (replication) and should be long enough to cover the period of interest.
Dendrochronology is regularly applied to determine the age of stringed instruments such as violins, violas, and cellos1,9,10,11,12,13. For stringed instruments, the wood of the top plates (also the front plate, belly, or soundboard) can be dated. They are usually made of Norway spruce (Picea abies) or silver fir (Abies alba)4,6,13. The measurements must be made in a non-invasive way directly on the instrument or by using images. The measurements are usually made at different locations on the top plate to establish a sequence for the instrument that can be dated with reference chronologies.
Dating is the most critical step because a reference chronology must be available for the species, geographic area, and time period of the instrument being studied. Many chronologies are available at the International Tree Ring Data Bank (ITRDB)14, but only a few are of Norway spruce or silver fir from the region covering the period of interest6; therefore, dendrochronology laboratories put a lot of effort into constructing reference chronologies. The likelihood of dating increases if a network of chronologies is available, including those from exactly defined forest sites, dated instruments, and instrument collections from various manufacturers like the Stradivari, Guarneri, and Amati families from Italy5,6,15,16, Jacob Stainer from Austria, as well as Joachim Tielke and members of the Hoffmann family from Germany17,18,19. The fine historical instruments made by the manufacturers in the 16th century to 18th century are most prized by musicians and collectors, although the importance of many less-known makers is also growing3,4,6,12.
Dendrochronology provides the end date, which must be considered the terminus post quem – the year after which the instrument was made. Dendrochronology is also used for dendroprovenancing, which helps to determine the geographic origin of the wood and to assign instruments to specific violin makers or violin-making schools3,4,6.
The dendrochronological end date almost never coincides exactly with the year the instrument was made, and the latter must, thus, be estimated, which requires a lot of supporting information and cooperation between experts of different fields.
1. Inspection and description of a stringed musical instrument - violin
NOTE: Violins are the most frequently investigated stringed instruments. Therefore, we describe the procedure on a violin.
2. Selection of the locations for measurements on the musical instrument
3. Capturing digital images
4. Measurement of tree ring width
5. Data processing, cross-dating, and building the chronology of the instrument
NOTE: For cross-dating, a specialized program and suitable reference chronologies are needed.
6. Dating of the instrument
Figure 2: Detailed representation of the steps of the protocol. (A) A violin with the top plate made of two resonance boards (bass and treble); (B) scanning of the top plate; (C) part selected for the tree ring width (TRW) measurement (precision 0.01 mm) and measurement direction from the bark to the pith (which were outside the board); (D) tree rings as bands on the radial board and the TRW measurement direction from the darker latewood to the light colored earlywood; asterisks indicate where the two boards with end dates of 2003 and 1995 are glued together; +1, +2, +3… denote the locations of the tree ring boundaries (+) and the tree ring numbers (1, 2, 3); scale bar = 1 cm; (E) tree-ring series of the treble and bass side of a violin in cross-dated position and end dates 2003 and 1995 indicated; (F) different end dates of the two boards due to different numbers of tree rings being removed during the manufacturing of the instrument; (G) orientation of the resonance board in the tree and the tree rings corresponding to the end date and the last tree ring below the bark formed before the tree was cut. Please click here to view a larger version of this figure.
A typical case in which a dendrochronological study was requested is a violin allegedly made by Andrea Guarneri of Cremona belonging to the family/school that produced numerous valuable instruments16,24. The violin in question contained two labels. One stated that the instrument was made by Andrea Guarneri of Cremona in 1747, while the other stated only 1867. However, the organological examination of the violin (Figure 3) suggested that it was probably of German origin and about 300 years old.
Figure 3: The historical violin, dated by dendrochronology. (A) The top, (B) the back, and (C) the scroll of the violin, which contained two labels with the inscriptions (1) Andrea Guarneri of Cremona in 1747 and (2) 1867. The top plate was made of two resonance boards (bass and treble), and the end date of the youngest tree ring (arrow) on the plate was dendrochronologically determined to be 1640. The instrument was probably made a few years after 1640, as the Δt-interval (the number of years between the end date and the date of manufacture) averaged 14 years for many instruments of Jakob Stainer who probably made the instrument. Please click here to view a larger version of this figure.
The top plate of the violin was made of two radial boards of Norway spruce (Figure 3A). The tree rings were very narrow, averaging 0.69 mm (ranging from 0.28 mm to 1.25 mm) and locally poorly visible due to the surface treatment (dark varnish). Therefore, the measurements were repeated several times at several locations on the instrument. Dendrochronological cross-dating of the series of the two resonance boards revealed that both originated from the same tree, so that they could be averaged to a 141 year chronology of the instrument (Figure 4).
The dating was performed by experienced dendrochronologists using reference chronologies from the laboratories of the University of Hamburg, the University of Ljubljana, the BOKU University of Vienna, the Laboratory for Dendrochronological Analysis of Musical Instruments and Objects of Art25, as well as chronologies published in the ITRDB14. Over 110 reference chronologies of spruce from different forest sites, historic buildings, individual instruments, and instrument collections of known violin makers were used, covering the period from 1137 to 2009. In more than 70 cases, the same end date of 1640 was defined25, which must be considered the terminus post quem, meaning that the tree for the board was felled after 1640 (Figure 4).
Figure 4: Tree ring series of the historical violin dated with a reference chronology. Tree ring series of the violin (red line) with the end date 1640 terminus post quem, and a published reference chronology of a high elevation Alpine stand in Austria26 (black). The statistical parameters of agreement are: OVL = 141, GLK = 63**, TVBP = 5.0, and TVH = 5.6. Please click here to view a larger version of this figure.
The statistical parameters of dating showed the best agreement with the chronology of instruments made by the violin maker Jakob Stainer (1618/1619-1683) from Austria (OVL = 141, GLK = 66*** [99.9% confidence]4,20, TVBP = 7.4, and TVH = 8.7)25. The same date and good agreement were also found when dating with various chronologies from Austria and southern Germany, as well as instruments made by Austrian and German violin makers. Jakob Stainer was a famous violin maker in Austria, known for his outstanding instruments, which he built in Innsbruck, Vienna, and for various orchestras throughout Europe17.
In this way, the most probable violin maker (the workshop) and the geographical area of the wood source were suggested. On the other hand, dendrochronology could not give a more precise date (year) for when or how many years after 1640 the instrument was built. This depends on how many tree rings (from the outside of the tree) were removed by the craftsman during the woodworking and making the instrument and for how many years the wood was dried and stored.
However, it is estimated that the instrument was made a few years after 1640. This assumption is based on information that the Δt-interval (i.e., the number of years between the end date and the date of manufacture of the instrument)27,28 averaged 14 years for Stainer's instruments17 with original labels examined by various experts.
Is the instrument then original or fake? The instrument presented here was most probably not made by Andrea Guarneri, as one of the labels claims, although it was made during his lifetime (1626-1698). The dendroprovenance suggests that the wood came from Austria or Germany and that the instrument was probably made by the Austrian luthier Jakob Stainer (1618/1619-1683), a contemporary of Andrea Guarneri. The instrument was built after 1640 and is thus much older than the inscriptions on the labels (1747 and 1867).
The presented protocol describes the procedure of the dendrochronological dating of a violin. The procedure includes several critical steps. The first one is to identify the tree rings in order to properly measure their width. This is critical because the tree rings are often very narrow or have unclear boundaries due to the small amount of latewood (step 1.3). The detection of tree rings can be complicated by aging of the wood, dark and opaque varnishes28, or damage, repairs, retouching, or dirt (step 2.2).
However, it is possible to modify and improve tree ring detection (and measurement) by using high-resolution cameras4,15 and advanced microscopy techniques to acquire high-quality images (e.g., confocal laser scanning microscopy [CLSM])28 supported by advanced software that allows the stitching of multiple images29,30. A very promising and increasingly widespread technique is X-ray computed tomography (CT), which allows virtual cutting of the instrument and observation of the tree ring structure in different views31,32,33.
Once a reliable tree-ring series is established (step 4.4), dendrochronological dating follows. This is another critical step because it requires the use of appropriate reference chronologies for dating, as described in step 6.1.
As mentioned earlier, dendrochronological dating also has its limitations. First, we may not have an adequate reference chronology, or there may be no chronology for a particular area or time period, and, therefore, dating may not be possible. Another limitation is that dendrochronology only gives the end date (i.e., the year in which the last tree ring measured on the instrument was formed). Therefore, the year of manufacture must be estimated (step 6.2). According to the literature, the number of years between the end date and the date of manufacture of the instrument ranges from a few years to a few decades13,23,27.
In any case, dendrochronology is a significant scientific dating method based on the comparison of tree-ring patterns, which depend on the climate and the physiology of the tree species, supported by statistics6,27. In contrast, other commonly used methods depend on other sources of information, such as the label on the instrument, which is often not reliable, and the inspection of the instrument and its parts. Furthermore, dendrochronology can be used for dendroprovenancing, the determination of the geographic origin, as well as the luthiers or schools that made the instrument.
Given its strengths and the expected future improvements in imaging techniques, networks of reference chronologies, and the dendroprovenancing method34, dendrochronology, in combination with other techniques, is expected to remain an important tool for dating and authenticating stringed instruments of valued and lesser-known makers. For optimal use, it is important to know the procedure, although it is recommended that an expert performs the analysis and interpretation of the results.
The authors have nothing to disclose.
This study was supported by the Slovenian Research Agency (ARRS) Program P4-0015 (Wood and lignocellulosic composites) and the Young Researchers' Program.
CDendro | Cybis Elektronik & Data AB | https://www.cybis.se | program CoDendro for dendro data management and crossdating |
CooRecorder | Cybis Elektronik & Data AB | https://www.cybis.se | program CooRecorder to measure tree ring widths on images |
TSAP-Win | RINNTECH | https://rinntech.info/products/tsap-win/ | Time series analysis software |