continually modifies its warp. The RH considered suitable to ensure the
stability and uniformly flat surface of the wooden support varies between
55% and 60%. A polyvinyl acetate (PVA) emulsion was used to adhere the
wedges, since its strength and moderate elasticity enable it to adapt better
than other glues to the conservation needs of wood.Support control system
After repair and reconnection of the joins, reconstruction of the missing
wood parts, and reinforcement of the junction of the lap join, the support
appeared quite solid. The only remaining phase was the construction and
mounting of a crossbar system to control and reinforce this particular
construction.
The author selected a system that could simultaneously respond
to the expansion and contraction and, in addition, serve as a sound rein-
forcement, assuming the role of a true load-bearing structure. A perimeter
strainer, or framework, was built with crossbars made of laminated oak
from Slovenia. The crossbars had the same 9 mm curvature as the support,
so that the strainer would conform to the shape of the panel. The frame-
work was attached to the support without leveling of the back surface.
Instead, small wooden spacers were inserted at the attachment points
where the contact between the two parts was not perfect. A special mecha-
nism to unite the two parts allows for potential expansion and contraction
of the support and regulates possible warping of the planks. This mecha-
nism consists ofa brass shoe in the formof a closed U-channel section,
held to the back of the support with a single screw (Fig. 8). Inside this
U-channel section glides a nylon slide with a bolt at the center. The bolt
passes into the framework through a brass sleeve, in which there is a
spring regulated by a nut.^10
The invasiveness of this mechanism to the painted support is
limited to a single screw for each element. The presence of the spring
between the support and the framework facilitates the regulation of stress
and possible slippage between the two parts, as well as reduces tension.
Designed to respond to problems of tension and deformation that may
appear over time, the mechanism is extremely simple and does not require
any intervention to the support (Fig. 9).
The selection of a means of deformation control with a frame-
work system goes against the concept of the traditional crossbars, which
act as a load on the support. Instead, the framework is a load-bearing
structure to which the painting is anchored by means of attachments freed
from mechanical tensions. In addition, if the RH of the exhibiting environ-
ment is uncertain, the framework makes it possible to enclose the back of324 Castelli
Figure 8
Example of the mechanism that attaches the
framework to the painting support.