Tree Rings and Culture (and Us)

About Archaeology Guide Kris Hirst has blinded me with science in an article chock-full of facts on tree rings and culture, also known as dendrochronology. She explains what this is, who discovered it, how long chronologies (or "master curves") are established for different species and the ways in which dendrochronology provides useful information for archaeologists, biologists, geologists, those studying silviculture and historians in general.

You may be wondering why I bring this up, so here's why: it applies to art history, too. Dendrochronology is one tool in the technical examination arsenal, if you will, used for determining the age of a painting on wood or a drawing on paper. It's not as easy a science to use in our discipline, for we are seldom given access to nice, big cross sections of trees in works of art. To use dendrochronology on a thin piece of wood or paper, certain conditions must be present. The wood has to be of a species we've got one of those master chronologies on, we ideally need at least 100 rings in the sample to get a good match on dates, and allowances must be made for (1) seasoning time, (2) lack of bark and (3) loss of rings in the manufacturing process. One also needs a microscope capable of fairly high magnification to properly examine the (necessarily minute) sampling of wood. However, this is a science that authenticators use whenever feasible because it tells us so much.

For example, Leonardo da Vinci's La Gioconda (popularly known as Mona Lisa, ca. 1503-05) has wood for its support. Identifying it specifically as poplar is easily done by eye, looking at its color and grain. (Were this not so easy, "poplar" is a fairly safe bet as a support panel for this time and place. It was a popular choice with artists during the Italian Renaissance - not least of which because it grows abundantly in the region.) Measurement shows the wood is 12-13 mm thick; another characteristic of poplar is that it must be planed more thickly than say, oak, because it is a "soft" wood. And dendrochronology tells us that, even though it went on to achieve a sort of immortality as part of the greatest art historic icon going, this particular poplar tree ceased producing growth rings prior to 1503.

Now, currently on display at Dulwich Picture Gallery is a fine copy of the Mona Lisa. So fine, in fact, that its former owner Sir Joshua Reynolds (1723-1792) was 100% certain that it, too, had been painted by Leonardo. It truly is a remarkable copy, being in a much more well-preserved and clean state than the original. I've stared at the image of the copy for long periods of time, delighted to see its unfaded colors and the clarity of the landscape in the background.



It's simply grand, isn't it? Whoever the anonymous copyist was, he was tremendously skilled. But! Here again, dendrochronology comes into play: we know, as Sir Joshua could not have, that the support panel of this painting is from a species of oak found growing in the Baltic region. And even if Leonardo could have gotten his hands on this type of wood - which is highly improbable - the tree from which this panel came was felled after 1602, at least 83 years after Leonardo's death.

I'd urge you to give Kris' article a read for the low-down on the science of dendrochronology, and doubly urge you to go and visit this copy, on display at Dulwich Picture Gallery, London until February 11, 2007. Science and art - they go hand in hand much more often than is acknowledged.

Image credits:

Leonardo da Vinci (Italian, 1452-1519)
Mona Lisa (La Gioconda), ca. 1503-05
Oil on poplar wood
77 x 53 cm (30 3/8 x 20 7/8 in.)
Musée du Louvre, Paris

French School
Copy of Portrait of Mona Lisa,
after Leonardo Da Vinci, probably
early seventeenth century
Oil on oak panel
65.3 x 53.4 cm (25 11/16 x 21 in.)
Private Collection
Image © Courtauld Photographic Survey
Photograph provided by Dulwich Picture Gallery