[Information found in the previously posted papers on Stradivari's varnish analysis and historic bass-bars may be found in my new book, Stradivari, published by Cambridge University Press in 2010. The paper posted below was given at the International Workshop on Diagnostics and Preservation of Musical Instruments, University of Bologna, Ravenna, May 20-21, 2010. An earlier version of this paper was published in the Newsletter of the Michigan Violinmakers Association, April, 2010.]

Dendrochronology: Tool of Truth or Deception?

By Stewart Pollens

2010

Dendrochronology, which may be defined as the dating of the year rings of wood, has only recently been employed in the dating of violins. In 1953, Lottermoser and Meyer attempted a relative dating of Italian stringed instruments by comparing the year-ring patterns of three violins, though actual dating was not achieved until the 1980s by Corona, Schweingruber, and Klein.[i] In 1994, when I helped organize the Guarneri del Gesù exhibition at the Metropolitan Museum of Art in New York, I invited one of the world’s leading dendrochronologists, Dr. Peter Klein of the Ordinariat für Holzbiologie of the University of Hamburg, to date the spruce tops of the twenty-five violins assembled for that exhibition. Among the conclusions gleaned from Klein’s findings are that Giuseppe Guarneri apparently did not use well-aged wood in making his instruments (the last datable ring is often just a few years earlier than the date on the violin’s label), and that he occasionally used mismatched pieces for the tops (whether this was by design, disinterest, or carelessness remains a matter of conjecture).

    I had met Dr. Klein many years before the Guarneri exhibition, for in the 1980s and 1990s, he was often invited to the Metropolitan Museum of Art to date panel paintings, and I would buttonhole him in the staff cafeteria and ask him to date the wood of one or another instrument that I was then studying or restoring, including violins, viols, lutes, guitars, and harpsichords. I never had any reason to question his findings, which were always in agreement with my assessments. A few years after the Guarneri exhibition, I employed his services in dating the wood used to make the “Messiah” violin. Though he initially determined that the last datable year-ring of that instrument was 1738, which postdated Stradivari’s death, members of the violin trade maneuvered him into temporarily retracting his findings in exchange for an opportunity to re-measure the “Messiah’s” year-rings at the Ashmolean Museum; however, because of a dispute that developed during that session, he was unable to leave the Ashmolean with his measurements. Klein now declines to date violins, which is a great loss to those of us who formerly relied upon his expertise and objectivity.

   Then John Topham, and subsequently, Dr. Henri Grissino-Mayer entered the fray. Though lacking formal training in dendrochronology (in the case of Mr. Topham), as well as experience in the dating of objects (Grissino-Mayer is primarily involved in the use of dendrochronology in the study of climate history) and, most importantly Klein’s proprietary master Alpine spruce chronology, Topham and Grissino-Mayer claim to have re-established the “Messiah’s” authenticity by employing what they call a “floating” chronology derived from the “Archinto” and “Kux-Castelbarco” Stradivari violas. Unfortunately, their chronology only extended to 1685, and as dendrochronologists Angelo Mondino and Matteo Avalle pointed out, this did not permit Topham and Grissino-Mayer to discover a more compelling statistical match further along in time.[ii]  In 2005 Mondino and Avalle asserted that the last year-ring of the “Messiah” grew in 1788, fifty-one years after the death of Antonio Stradivari, though in a more recent study, they claim to have discovered an even later date, 1844.[iii]  

  Disturbed by the multitude of conflicting dates, I decided to delve more deeply and directly into this dating technique in the hope of learning more about it and, perhaps, determine why dendrochronologists have arrived at so many different dates for the “Messiah.” In 2007 I purchased the Synchro Search computer program and the accompanying Manual of Dendrochronology Applied to the Dating of Musical Instruments written by Angelo Mondino and Matteo Avalle (Cremona Books, 2005). Synchro Search is a graphing and statistical program for comparing year-ring data with established master spruce chronologies. The program disk includes a number of master chronologies that are in the public domain, including the Ötztal-Obergurgler, Siebenlist-Kerner Ötztaler, Obersaxon-Meierhof, Schweingruber, and Malcolm chronologies, which are among the chronologies that have been used in dating violins. In using the Synchro Search program, the graphed year-ring dimensions of the violin in question can be advanced with the click of a computer key against graphs of any of the master chronologies until a match is found.  As one proceeds, the program automatically computes statistical data, including Gleichläufigkeit (similarity or G index), Pearson’s r correlation coefficient (see below), Student’s t, mean sensitivity, serial correlation coefficient, overlapping index, and linear regression. The program can also be set so that the computer will locate the best matches, which is very convenient when master chronologies are hundreds of years in length.

   In my investigation of this dating procedure, I did not wish to muddy the “Messiah” waters any further, so I decided to use Synchro Search in an attempt to establish the age of a large (17 ½”; 444 mm) viola, apparently Brescian, that the late Jacques Francais attributed to Gasparo da Salò (1540-1609).  Making year-ring measurements of an old, heavily restored violin or viola top can be difficult.  There may be “patches coming through” made with transplanted or later wood, painted year-rings, as well as dents, scratches, and heavily discolored or retouched varnish that obscure the grain. One must be aware of seams, wings, and grain direction.  If even a single year-ring is missed, this can prevent the discovery of a match with the master chronology, so one must be very careful in measuring.  At that time, Klein used a little 7X loupe fitted with a metric scale that came in contact with the surface of the instrument. The advantage of this device is that it can be carried around in a pocket; the disadvantage is that it must be pushed along the surface of the instrument as one moves from year-ring to year-ring. When using a loupe, it is necessary to call out the measurements to a recording secretary, and this is another inconvenience. I devised a piece of equipment that is more accurate and convenient to use—unfortunately, it is cumbersome. It consists of a low-power stereo microscope (mine is an Amscope 7-45X on a boom stand) with one eyepiece fitted with a cross-hair reticule. Below the microscope, a violin/viola cradle (International Violin Co. #T-97) is attached to a 250 mm rack-and-pinion linear translation stage (Edmund #R56-796) that is linked via a brass angle bracket to a 12”-300 mm Mitutoyo Digimatic linear scale with SPC output (see figure). To use this device, I clamp the instrument (with its strings, bridge, and tailpiece removed) in the cradle and start by aligning the earliest year-ring (which is typically the ring at the edge of the lower bout of the instrument—though one should carefully check the year-ring shading to make certain of the orientation) with the cross hair in the microscope’s eyepiece. Using the rack-and-pinion of the translation stage, I then carefully align the next year-ring against the cross hair and press the button on the linear scale’s output device (see figure). This enters the measurement into a Microsoft Excel spreadsheet, which I have programmed to subtract the previous measurement from the last one entered, so that I wind up with a column of year-ring widths. Most violins have tops made with book-matched slabs of spruce, so one must stop at the center joint. These tabulated widths should then be multiplied by a factor of 100 so that the graphed data can be more readily compared to the master chronologies (dendrochronologists work in units of 1/100 mm, so 1 mm is expressed as 100).[iv] The column of figures must then be copied out of Excel as a text file (.txt file extension) so that the data can be “processed,” or compared against any of the master chronologies that are supplied with the Synchro Search program.

    Returning to the Brescian viola: I compared my 74 measurements of year-rings from the treble side of the instrument to the following master chronologies: PCAB Giertz Obergurgler 1276-1974, LADE Siebenlist Obergurgler 1511-1974, PCAB Schweingruber Obersaxen 1537-1995, and Media 46° 1276-1994. I employed a straightforward matching of the year-ring sequence with these master chronologies and did not use indexing, segmentation, or any of the other statistical manipulations that dendrochronologists often resort to.  Tabulated below are the final dates for the viola’s treble-side sequence where there was 60% or better Gleichläufigkeit (G index or similarity) with each of the master chronologies. This was chosen as a cutoff point because it represents a degree of probability of over 95%, and because this percentage of agreement between the year-rings of an object and a master chronology is sometimes considered a “match” in dendrochronological reports and literature.[v]  The reader may be surprised by the number of “matches” that were found:

                                             Final Year       Gleichläufigkeit

PCAB Giertz Obergurgler                    1350                62.3%

                                                            1417                61.6%

1445                65.7%

1463                65.7%

1500                61.6%
            1522                62.3%

1540                60.2%

1554                64.3%

1572                65.7%

                                                            1583                63.0%

                                                            1600                62.3%

                                                            1618                61.6%

                                                            1732                63.6%

                                                            1756                62.3%

                                                            1758                65.7%

                                                            1839                63.6%

                                                            1863                62.3%

                                                            1901                65.0%

           

 

LADE Siebenlist Obergurgler                1511                62.3%

                                                            1665                65.0%

                                                            1680                62.3%

                                                            1704                63.0%

1732                63.0%

1750                60.9%

1792                60.2%

1810                60.9%

1826                63.0%

1826                65.7%

1834                65.7%

1949                65.0%

 

PCAB Schweingruber Obersaxen         1690                61.6%

                                                            1756                65.0%

                                                            1758                62.3%

                                                            1784                64.3%

                                                            1810                65.0%

                                                            1895                63.0%

                                                            1925                60.9%

                                                            1953                67.8%

                                                            1959                60.9%

 

Media 46°                                            1522                62.3%

                                                            1551                63.6%

                                                            1572                63.0%

                                                            1611                60.2%

                                                            1625                60.2%

                                                            1657                70.5%

                                                            1665                65.0%

                                                            1696                60.9%

                                                            1710                60.9%

                                                            1712                62.3%

                                                            1732                60.9%

                                                            1754                62.3%

                                                            1756                63.6% 

 

  At 60% Gleichläufigkeit or higher (representing a probability of 95% or better), 52 matches were found, and at 65% Gleichläufigkeit or higher (representing a degree of probability of around 99% or better), 13 matches were found (with final dates of the series ranging from 1445 to 1953). It is also disconcerting that the PCAB Giertz Obergurgler, LADE Siebenlist Obergurgler, and PCAB Schweingruber Obersaxen master chronologies produced very few dates in common (1732 and 1756); the Media 46° chronology exhibited several concordances (1522, 1572, 1665, 1732, and 1756), but this would be expected as it is a composite derived from over thirty chronologies, including the other three that I used. The 1657 date (which has the highest Gleichläufigkeit of 70.5% and a probability of 99.9%) is of interest because violas of this large size were still being constructed at this time, though if correct, it would rule out Gasparo da Salo as the maker, as he died in 1609. However, I should point out that I subsequently discovered a date of 1805 with a considerably higher Gleichläufigkeit of 75.3% using the CEBR Schweingruber Ceader Valley (Cipro) chronology. I must admit that I did not initially seek a match with this master chronology because its synchronization dates extend only from 1675 through 1981, and my inclination was to search for dates using master chronologies that had earlier starting points. This only demonstrates that a supposedly “objective” person, such as myself, may overlook a master chronology because its inclusive years appear to fall outside the date that one hopes or expects to find.   

    In general, my experiences with the Alpine master chronologies supplied with the Synchro Search program (which include the PCAB Siebenlist-Kerner Ötztaler and PCAB Gierz Obergurgler chronologies that were employed by Grissino-Mayer, et. al., in fixing a date to their floating chronology when attempting to date the “Messiah”) have not yielded overwhelmingly convincing matches with a number of Italian instruments that I have tried to date.[vi]  The reason for this may be due to the fact that these master chronologies were constructed from wood samples taken from Alpine regions or altitudes that do not have precisely the same climatic conditions as the locale where the Cremonese and Brescian makers obtained their wood, which I believe was likely from the Italian Alps directly north of Brescia. Many of the master chronologies in the public domain are derived from wood found in the Ötztal and Obergurgl mountain ranges, which are close to Innsbruck, Austria. It is also possible that the Synchro Search program itself is at fault—some dendrochronologists have been critical of certain of its statistical operations, including its method of calculating Pearson’s r correlation coefficient and Student’s t.[vii]  However, determining Gleichläufigkeit is fairly straightforward, and it is often the only measurement cited in dendrochronological reports, including those of Peter Klein.  

    In conclusion, I would strongly advise violin historians, authenticators, appraisers, and purchasers to be extremely wary of the dates that are being published in auction catalogs, certificates, and scholarly journals.    

                       

Back to top of page