converge or diverge as the other end of the joint is approached. Slight cor-
rections may be made by bending softer woods back into alignment at
later stages, but some distortion and stress are then built in as well.Auxiliary support of larger panels
Despite such rare examples as the Turners mentioned above, larger panels
generally have substantial reinforcements (Fig. 6b, c). A higher ratio of
cross-grain dimension to thickness becomes a greater concern with large
panels of higher wood density. The structural implications can be greater
for certain panel structures, such as those with horizontal planks. Even
with sound joints, the Mengs tended to buckle under its own weight if
stood on its bottom edge. Most of the wood was sufficiently sound and
strong to withstand even quite severe bending stresses, but the joints will
always be weaker.^50 When there is already a set warp, buckling tendency
worsens as the panel warps further out of plane because of humidity
fluctuations. Such fluctuations would aggravate buckling even if the panel
were relatively flat at a particular humidity.
So, with reference to these concerns, the final and most challenging
difficulty, as with many large panels, was supporting the Mengs in an
upright position without restricting movement too greatly. The disjoins,
the inadequate balsa laminate, and especially the metal edge strips were no
surprise considering the panel’s structure, weight, and thinned state. The
critical point, however, is that a relatively rigid form of reinforcement is nec-
essary nonetheless for such large, thin, heavy panels, and the panel structure
must be sufficiently sound to take potential stress without rupture.
The Palmezzano is also a good example of a large, thin, weakened
panel requiring overall reinforcement of a specialized type. Internal frac-
tures remain in many panels after structural treatment, partly because they
are difficult to detect, even with radiography, especially in fibrous, lower-
density woods such as poplar.
The inherent weaknesses of panels such as the Palmezzano can-
not be overemphasized. A sympathetic but effective auxiliary support is
necessary in such cases. Truly satisfactory reinforcement designs with
proven effectiveness are still being sought for panel paintings of this
nature, as evidenced by the increasing amount of literature on new and
modified reinforcement designs.^51
When this article was written, an auxiliary support was being
designed and tested for the Mengs. It is therefore not presented here.
However, an auxiliary support applied to the Palmezzano is described.
The support was designed to allow greater movement, reduce the risk of
further splits and damages, and give adequate reinforcement.
The design is based partly on those developed at the London
studio of the HKI (Fig. 17a–c) (see Bobak, “A Flexible Unattached Auxiliary
Support,” herein; Marchant, “Development of a Flexible Attached
Auxiliary Support,” herein; Brewer 1994c). So far it is the largest ver-
sion that attempts to realize the main principle of tailored flexibility.
Horizontal tapered battens and a peripheral frame were constructed
from Sitka spruce (Picea sitchensis [Bong.] Carr.), and oak uprights were
attached to the horizontal battens to form a supporting lattice. The hori-
zontals were dovetailed into the peripheral frame for strength during han-
dling. The peripheral frame extended beyond the edges of the painting,
and a surrounding border of thick card projected up to 5 mm in front of468 Brewer