The Structural Conservation of Panel Paintings

the section entitled “Matching the Support to the Panel,” below.) In all

cases the flexibility of the battens and back springs combined must be

gr eater than that ofthe panel in order to ensure that the support yields

to the panel.

Back spring

The flexibility of the back spring will determine the preload that keeps the

panel in position against the frame rabbet and the ability of the panel to

become concave or to decrease its curvature (Fig. 11). The flexibility of

the back spring can be varied by increasing or reducing its width, b,

increasing or reducing its thickness, d,or altering its span. These three fac-

tors can be adjusted according to the panel’s size, weight, and curvature.

It should be clearly understood that the deflection of the back

spring is in a constant ratio to load, and most ofthe forces generated by

the panel will be referred to the central area of the panel parallel to the

gr ain if it becomes concave or reduces its curvature from the neutral slip

shape. Thus, of the two flexible parts, the back spring can have the more

critical influence. However, this fact should be balanced by the knowledge

that most problems occur when panels are restrained from becoming con-

vex (viewed from the front) rather than from becoming concave.

A F U A S 377

Figure 7, above
Flexible support spring assemblies on a
backboard.

Figure 8, above right
Apanel in place on flexible support spring
assemblies.

Figure 9, right
Model ofthe spring support assembly with a
panel at a neutral curvature profile (55% RH).

Figure 10, below
Model of the spring support assembly with a
panel at an increased curvature (low RH) in
comparison to that shown in Figure 9.

Figure 11, below right
Model of the spring support assembly with a
panel at a decreased curvature (high RH) in
comparison to that shown in Figure 9.