species, each having its own individual technological properties.” The
conservation and behavior of a wooden support during its lifetime are
significantl y influenced b y the wood species used. The selection of a wood
species for a panel depended on technical, economic, and practical factors.
It was also influenced b y the particulars of the artisan traditions.
As already mentioned, earlier supports were made mostly of
coniferous wood, especially fir (Abies albaMill.). Later, beginning in the
second halfof the thirteenth century, poplar (Populus alba L. and other
Populusspp.) started to be used on most panels throughout central Italy.^3
Other wood species have also been used occasionally through the cen-
turies, including walnut (Juglans regiaL.), linden (Tilia cordataMill.), oak
(Quercus spp.), chestnut (Castanea sativa L.), and others.^4 Engaged frames
were mostly made of poplar (especially the earlier examples, which were
manufactured integrally with the panel), since the same wood properties
were required for the engaged frames as for the panel. The framework on
the back (including the crossbeams) was usually made of wood species
selected for their strength and rigidity.
The choice of wood by local artisans was strongly influenced by
questions ofavailability and cost. Marette shows that wood species for
supports were typically chosen among those growing in the region
(Marette 1962).
This and a number of other reasons help explain why poplar was
the species most frequently used for panels. Poplar is technically suitable
for the manufacture of supports. Poplar’s heartwood is undifferentiated,
and the absence ofextractives such as tannins makes adhesion ofglues
and ground layers easier and more secure and prevents leaching and stain-
ing in the event of high moisture. It is homogeneous, being fine textured,
with not much difference between earlywood and latewood, or between
normal wood and knots. Poplar also exhibits good dimensional stability in
the presence of humidity variations, due to its small shrinkage and distor-
tion coefficients. Moreover, it is strong, light, and easy to dry and process.
It offers a plentiful source of large, regular, straight-grained, and relatively
defect-free boards. As for its availability, poplar’s natural growing area
covers practically all of Italy.
The major drawbacks of poplar are its low natural durability
against fungi and its nonresistance to wood-boring insects, both a con-
sequence of the absence of extractives.
There is little doubt that poplar (and other similar but less used
species, such as linden and willow) was technically a better choice for
panels than was fir, the species that had been most widely used previously.
Fir is as fine textured and easily processed as poplar, but it is not as homo-
geneous. With fir, alternating earlywood and latewood tend to show up
through the thinner ground layers, and knots are more frequent and
prominent. In addition, fir has less dimensional stability than poplar, and
it reacts more quickly to changes in environmental humidity.
Until the middle of the thirteenth century, techniques used in
northern Europe, including the use offir, influenced those in central
Italy. At some point, however, the idea may have emerged that poplar
would fare better in the highly variable Tuscan climate, which subjects
panel paintings to great mechanical stresses. This idea may have been a
consequence of the greater autonomy in social, political, economic, and
artistic spheres in Florence beginning in the thirteenth century. This114 Uzielli