The Structural Conservation of Panel Paintings

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  of panel paintings that have been thinned

and cradled exhibit damage caused by the cradle or signs of stress

from it. Environmental conditions play a large part in this equa-

tion. Much can be done by altering the environment to achieve stability,

even with the cradle left largely unaltered.

However, many panels are so stressed or damaged by the cradle

that it is essential to remove it. Some thinned panels areself-supporting

but vulnerable after removal from the cradle, basic consolidation, and

rejoining. Their response to environmental changes can be rapid and dam-

aging. In some cases an unattached auxiliary support can offer further pro-

tection and stability—more than that provided by careful framing and

fitting of backboards. The auxiliary support allows reduced movement of

the panel within set limits. The panel is able to become alternately convex

and concave with changes in relative humidity (RH) while being retained

in the panel tray.

The reasoning of the cradle maker when thinning and fitting a cradle to

apanel is as follows: The panel is thinned sufficiently to allow it to be

flattened without immediate obvious damage occurring, and the cradle

is then glued in place. It holds the panel in a flat plane while allowing

cross-grain expansion and contraction. The elements glued in the grain

direction are sometimes used to reinforce joins, damages, and splits while

retaining the sliding battens at suitable intervals. The sliding battens hold

the panel in a flat plane and provide rigidity for the complete structure.

Several factors have been either disregarded or underrated in the

design and construction of cradles. For example, the influence of the

glued members lying parallel to the grain should be considered, inasmuch

as the overlying areas of the panel are more stable, more rigid, less hygro-

scopic, and stronger than the unsupported areas; areas of adjacent stress

concentrations close to the glued members (Fig. 1)—where the stress tran-

sitions are greatest—can show effects such as those seen in Figure 2a and

2b; the relative freedom ofthe unsupported areas between the glued

members allows them to react to stress and develop “washboarding” from

differential movement movement (Figs. 2b, 3a), and the differential caused

by unequal stresses can result in, or exacerbate, blistering and flaking in

the ground and paint film. It is important to note that all ofthese points

Cradling

A Flexible Unattached Auxiliary Support

Simon Bobak