The Structural Conservation of Panel Paintings

tree rings, but in other cases even 200 rings may not be

enough. The number needed, of course, depends mainly

on the quality of the sample.

The final—and essential—result the art historian seeks is the identification

ofthe year oftree felling. The last ring under the bark gives the exact date

and even the season oftree cut, if it has been conserved. In preparing oak

panels for paintings, panel makers usually cut the planks radially with

regard to the cross section of the tree (Fig. 6). The bark and the light, per-

ishable sapwood were removed, thereby eliminating evidence of the latest

growth rings and making a determination of the exact felling year impos-

sible, as only the latest measured growth ring of the panel can be deter-

mined to the exact year.

Sapwood Estimation

and Seasoning

D A  P P 43

Figure 4a, b
Measurement ofgrowth rings: (a) using a lens
in the museum, and (b) using equipment for
tree ring measurements in the laboratory.

a

b

12 60 127 0 128 0 1290 1300 13 10 132 0C.E.

Righ t wi ng bo ard I Lo ss du e to edg in g Left wi ng boar d II

Le ft wi ng bo ard I

1.0

1.0

Wi

dth

of

an

nu

al

rin

gs

(m

m)

Figure 5 BladelinAlta rpie ce
Comparison of growth rings derived from
different boards of the Rogier van der
Weyden Bladelin Altarpiece. Staatliche
Museenzu Berlin, Preussischer Kulturbesitz,
Gemäldegalerie (inv. 535).