The Structural Conservation of Panel Paintings

Panel weight as a factor in evaluation

During the development of this type ofauxiliary support, the first panel to

be assessed had lines of weakness caused by fractures and worm damage,

which made evaluation of its strength very difficult. Due to its areas of

weakness, the panel was assumed to have little or no inherent strength.

The intention of calculating a lattice flexibility was to find one that would

provide the reinforcement to support the weight of the panel horizontally

within a safe limit of deflection.

The known factors upon which a judgment could be based for the

lattice flexibility were the weight of the panel and the change in curvature,

monitored at the lower limit of RH that the panel might reasonably be

expected to be subjected to in the future, measured at the outer long-grain

edges of the panel as the dimensional deflection from the center. The

panel weight, divided by twice the number of battens in the lattice, was

taken as the load that, when applied to one end of a batten, would produce

a similar deflection from the center as that previously measured in the

panel. Tapered battens were then produced to give the specified flexibility.

The result was that when the lattice assembly of battens was placed hori-

zontally on a central support and the panel placed on top, the panel weight

was adequately supported without the determined safe deflection being

ex ceeded. The degree of rigidity of the support was therefore considered

correct for reinforcement.

When the support lattice was completed and anchored to the

panel, the assembly was evaluated in the vertical plane and found to give a

satisfactory degree of restraint—it reduced the panel’s previous curvature by

about 30%. The panel could also be handled with much more confidence. It

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Rigid timber beam

used as retaining

bar to secure

assembly in frame

Backboard

thin plywood

Pressure pad

with foam core

Reinforcement

Mounting pads

with foam core

glued to batten

Backboard

reinforced with

section in center

Mounting pads

(one of each pair

glued to backboard)

Frame with slip profile

Panel

Flexible batten

Pressure pad

(central bearing)

Flexible bridging strip

Backboard

a bc

Figure 6a–c
The main stages in the development of an
auxiliary support system. With an unattached
support (a), when the backboard is removed,
the spring bridges and battens joined to it
come away, leaving the panel loose in the
frame. With an attached support, in its earliest
development (b), spring bridges are inverted
and attached to battens. When the backboard
is removed, the panel and secondary support
remain loose in the frame. With an attached
support, in its later development (c), the panel
and secondary support are retained by a fram-
ing bar. When the backboard is removed, the
panel remains secure in the frame.