Dendrochronology is a dating process that utilizes the examination of annual growth rings in trees. Using this method, an artwork’s creation date can typically be established within one year of accuracy.
This technique is particularly valuable for Old Master European paintings. Artists such as Cranach, Raphael, Dürer and Giotto painted on wood panels. Wood was the typical support for paintings until the 17th Century.
Every year in temperate climates, trees create a new layer of wood under the bark. In good years, the layer is thick; in years of drought or excessive heat or cold, the layer is thin.
There is reference data to cross-match with samples from many, but not all, trees. The reference chronology is made by overlapping tree-ring patterns from a series of progressively older trees. To ensure the most exact match, there must be a minimum of one hundred rings in the sample.
There is particularly good dendrochronological data for oak trees in Western Europe and North America. In England, the master chronologies for oak go back to 5000 B.C.