wherever necessary along the crack. By strategic placement of the screws
and the small blocks under the braces, either side of the split can be
pushed down or pulled up (Fig. 7). If the panel is very thin, little blocks of
wood can be temporarily glued onto the panel to hold the screws in the
areas that need to be leveled. The glue used for softer woods, such as
poplar and limewood, is mostly a polyvinyl acetate (PVA) emulsion glue
such as Vinavil, thinned with water.^2 Woodworkers point out that the
glue that oozes out is what ensures a lasting bond—meaning that the less
glue that remains between the wedge and the wood of the panel, the bet-
ter. For harder woods such as oak, a two-component epoxy glue such as
Araldite is used.^3
For those who are not master artisans, a simpler and quite
effective method was developed by Barbara Heller at the Detroit Institute
of Arts after she worked for many years in Florence (Heller 1983). She cuts
the grooves with a router and uses precut V wedges that are set in with
Araldite carvable paste.^4 The results have been very encouraging and seem
to be stable, especially in the case of softer woods such as poplar.
The movable crossbars are held in place by pegs, ornottole,that
are glued to the panel with an epoxy adhesive. The section of the cross-
bars is trapezoidal, and particular care is used in planing the sole and the
two side edges. To ensure a perfect glide, hot paraffin is applied to the
edges and polished, and the same is done to the face of the pegs.
The crossbars and pegs of the early 1950s were much heavier and
wider. The pegs were not only glued to the panel but also screwed on,
thus locally blocking the movement of the panel. Two or three wide
swaths were also planed flat across the panel to accommodate the width
of the crossbars with the pegs (Fig. 1). This method removed much of the
aged skin, something that is no longer done today. To overcome the irreg-
ularities of the panel, individual spacers are now fitted and glued between
the pegs and the panel.
The Opificio delle Pietre Dure restoration department at the
Fortezza da Basso has carried out more panel restoration than any other
institution in the world; consequently, it has gained a wealth of unique
experience. It has introduced and perfected many new systems that reduce
interference with the tendency of wood to move. Where deemed appro-
priate, the angle of the V-shaped cuts has been reduced at times from 55°
to just 7.5° with a special router bit (Castelli, Parri, and Santacesaria 1992).
Although this approach interferes less with the original wood, the wood-
worker does not have as much control with a router as with a handheld
chisel and therefore cannot cut as close to the original gesso layer; this
deficiency might, in time, result in a weaker joint (Castelli, Parri, and
Santacesaria 1992).
Other systems may be used to minimize the interference with
the original panel, such as the method of attaching the crossbars without
pegs. Instead, a system of sparsely distributed brass threaded inserts is
screwed and glued into the panel. The crossbars are slotted lengthwise at
the same intervals as those of the threaded inserts, and identically slotted
brass plates are set into the crossbars. These crossbars are then attached
with long bolts that fit into the center ofthe slotted brass plates and are
directly screwed into the threaded inserts glued into the panel. The bolts
are not tightened excessively, and a Teflon washer can be used to facilitate
lateral movement. A simplified version of this method consists of fasten-
ing the crossbars, which are also slotted, with long, round-headed brass310 Rothe and Marussich
Figure 7
Temporary tiranti, or levers, used to pull dis-
torted surfaces ofseparated panel boards back
into plane before wedges are glued into previ-
ously prepared grooves.