screws that are inserted directly into the original wood of the panel.
Unfortunately, if the crossbars need to be removed and reattached several
times, the screw holes will eventually wear out if this simpler method is
used. In either case, to prevent rusting, only brass screws and steel bolts
are used (Fig. 8).
At times panels need to respond in more than one direction to
humidity fluctuations. Expansion and contraction are sometimes aug-
mented by a tendency ofthe panel to warp—a tendency that, if impeded,
might cause the panel to split. For this reason methods have been devised
to add some form of spring action to the construction of crossbars. The
simplest method consists of adapting existing older cradles with springs
that are fitted into carved recesses at the junction of the braces and bat-
tens. For this purpose the battens are also thinned to facilitate movement
(Castelli, Parri, and Santacesaria 1992).
Another method improves the system of bolts discussed above in
the construction of new battens or the adaptation of original ones. It con-
sists of steel springs of approximately 2.5 3 7.5 cm that are lodged into
slotted and carved recesses in the crossbars so as to give the bolts ample
space to move and to allow the panel not only to expand and contract but
also to flex up and down (Castelli, Parri, and Santacesaria 1992). A more
sophisticated method makes use of conical springs that are inserted into
the crossbar.The brass nuts are held in place by pegs made out of lime-
wood glued to the back of the panel (Castelli, Parri, and Santacesaria 1992).
Asystem for thin panels that provides the most freedom of move-
ment consists ofa strainer that is constructed around the panel. The
strainer holds the panel in place with springs attached to small wooden
blocks that are glued to the panel. This system is not ideal for environ-
ments that have no climate control, as it does not offer enough restraint to
the panel: in some cases panels treated in this manner have deformed and
cracked. A much simpler and more effective solution in this case is the
mounting ofthe painting into its frame with steel springs, as has been
done at the Bavarian State Galleries in Munich (by Christian Wolters).^5
The newest methods, which are mentioned by Castelli (see “Restoration
ofPanel Painting Supports,” herein) deal with more sophisticated spring
mechanisms that permit panels to flex.
The guiding idea behind all these constructions should be to give
the panels ample room to move while at the same time exerting a certain
amount of restraint to keep them from deforming. The authors have
observed old panels—such as a painting by Lorenzo Sabbatini, Madonna and
Child Enthroned with Two Saints from the Staatliche Museen zu Berlin (Bode
Museum)—that have deformed because they have lost all or part of their
original restraints (Fig. 9). The general guideline is not to treat a panel if it
has survived in good condition, but if original crossbars are missing and the
panel has a tendency to deform, the crossbars need to be replaced. Wooden
panels need to be held in plane gently but firmly; otherwise they may
deform, especially if exposed to uncontrolled climatic environments, as is
the case with the great majority of panel paintings in the world.
Moisture barrierscan be of some help in the centuries-old drying
process of a panel by slowing down its constant response to changes in
humidity (Buck 1978). The most commonly used materials have been
Lucite 2044 or 2045 and Acryloid B72.^6 Saran and wax have also been used.^7
Fortunately, the unaesthetic and sometimes heavy constructions of wax
and balsa wood that have been used often in the United States and EnglandF S S T 311Figure 8
Various screws and bolts used in less invasive
types of crossbar attachments.
Figure 9
Lorenzo Sabbatini, Madonna and Child
Enthroned with Two Saints,ca. 1560. Reverse.
Oil on panel, 151.8 3 229.0 cm. Staatliche
Museen zu Berlin, Preussischer Kulturbesitz,
Gemäldegalerie. The loss of the central cross-
bar has caused severe convex warpage. The
dovetail insets are probably original.