Dendrochronology is the science of tree rings in the wood. It can be used to determine the age and origin of wooden musical instruments, like a violin. Dendrochronology clarifies in which calendar year a particular tree ring was formed.
We can estimate when the tree was felled, where it was growing, and when the violin was made. This protocol will help you to better understand how the dendrochronological analysis is performed, how to interpret the report, and how to determine whether, or not the violin is original. Dr.Angela Balzano, Nina Skrk Dolar, and Luka Krze, researchers from our laboratory, prepared the demonstration of the procedure.
We are collaborating on this project with Blaz Demsar, a violin maker from Ljubljana, Slovenia, who has provided the violins for the demonstration of the protocol. Dr.Micha Beuting, a publicly accredited and sworn expert for dendrochronological investigations on musical instruments by the Chamber of Commerce in Hamburg, Germany, who has helped us with reference chronologies, and demonstrated how a report should look like. To begin, examine the instrument and all its parts.
Take detailed photos of the top, back, side, scroll, and label, along with the measuring scale for reporting and archive. Examine the top plate of the instrument to understand its construction. Check whether the top plate is made of one, two, or more parts, and how they are joined together.
On the radial board of the top plate, examine the structure and orientation of the tree rings. The rings are seen as bands of annual growth layers, consisting of light colored early wood and darker late wood, and delimited by the tree ring boundaries. Based on the location and transition of early wood to late wood, determine which side is the bark and which side is the pith.
Usually, the most recently formed tree rings, which were closer to the bark, are located at the joint in the center of the top plate. First, inspect the widest parts on each piece of the top plate. Check for any damage, repairs, retouching, or dirt, and select the areas where the varnish is transparent enough to see the tree rings.
If the instrument is opened and the top plate can be removed, measure the tree rings on the underside of the top plate, where no varnish is applied. Ensure that the selected area has the greatest number of tree rings, and that the boundaries between the rings can be recognized. Using a magnifying lens, or stereo microscope, try to clearly see the tree rings that were near the bark for an accurate identification.
Mark the measuring line in the direction from the bark to the pith, and place a measuring scale on the board. For image analysis, place the top plate of the violin on the scanner, and scan the parts selected for the tree ring measurement using a resolution of 1, 200 DPI, or greater, and a high depth of field. For editing the images, use a graphics editing program.
Check the quality of the image, and adjust the color, brightness, and contrast to best see the annual growth rings and the boundaries between them, and save the images. Start an image analysis system, preferably one designed for the automatic and manual detection of tree rings and the measurement of tree ring width. Open the image and set the calibration by measuring the distance of a known length on the measurement scale as part of the image.
Start the measurement by clicking on the tree ring boundaries, and note whether the first tree ring measured is closer to the bark, or closer to the pith. To measure the distance between the tree rings, click the tree ring boundaries manually if the automatic detection of tree ring width is not possible, or requires too many corrections. Measure all the tree ring widths along the measurement line.
Save the data as the tree ring series with each tree ring width recorded for a specific relative year. The output of this measurement is a table of tree ring widths versus time in relative years. For data processing, open the data file containing the tree ring widths in millimeters against years.
For cross-dating, open the tree ring series to be cross-dated, and another tree ring series of the same instrument to serve as a reference. Run the cross-dating to move them into the synchronous position. Check for the main cross-dating parameters used in the study of violins.
Consider the parameters significant. The Baillie and Pilcher T-value, or TVBP, is a minimum of four, and the Hollstein T-value, or TVH, is at least four, and if the concordance coefficient, or Glk, percent is at least 65%Consider the overlap, which indicates the overlapping period of two tree ring series in years. When the two tree ring series are on the same relative timescale, save the position of the series.
Repeat this step until all the tree ring series of each board and instrument are cross-dated. Then to create the chronology of the violin, observe the graphs, and select those that have no measurement arrows. If the agreement between the series within the instrument is statistically significant, average all the tree ring series into one chronology of the violin.
Cross-date the chronology of the violin with several reference chronologies. Perform the cross-dating with the reference chronologies. Then check the parameters of the agreement and visually assess the proposed dating proposition.
For successful dating, ensure that the same end date is confirmed by multiple chronologies with statistically significant parameters, as well as by visual comparison of the sequences. As the final result of the dendrochronological analysis, report the end date indicating the year in which the last, or most recent tree ring on the top plate was formed when the tree was still alive. Use the information on the original label and other sources to estimate the number of years required for wood drying and storing, and the number of tree rings removed during wood processing.
Add this value, which usually ranges between 50 to 20 years, to the end date to propose the potential date of manufacture of the instrument. To validate the authenticity of the violin, confirm the assumptions about the age, maker, and area of origin. Write a report that includes the dendrochronological end date and sufficient information about the investigation that may help in the interpretation of the dating.
An historical violin was inscribed with two labels in the inside of the violin body, one stating that the instrument was made by Andrea Guarneri of Cremona in 1747, and the other stating only 1867. However, organological examination of the top, back, and the scroll of the violin suggested that it was probably about 300 years old. The top plate was made of two radial boards of Norway spruce.
The tree rings were very narrow, averaging 0.69 millimeters, and the end date of the youngest tree ring on the plate was determined to be 1640. Dendrochronological cross-dating performed using over 110 reference chronologies of spruce covering the periods from 1137 to 2009 revealed an end date of 1640. Tree ring series of the violin showed statistically significant similarity, and the end date 1640 was confirmed with more than 70 reference chronologies from different forest sites and historic buildings, mainly in Austria and Germany, as well as individual instruments and instrument collections of violin makers, like Jacob Stainer.
This result presents the dating with a widely used reference chronology of a high elevation alpine stand in Austria, constructed and published by Veronica Siebenlist Kerner in 1984. Thus, the instrument was built after 1640, and is much older than proposed by the inscriptions on the labels. In this procedure, one must clearly see the tree ring for correct measurements.
Also, adequate reference chronologies are needed for dating. Dendrochronology is often combined with other techniques, like the study of the label, and the inspection of the instrument and its parts. Dendrochronology benefits from the improvement of imaging techniques and promotes the development of networks of reference chronologies, and also the improvement of dendroprovenancing methods.
