at the beginning of the intervention, it became more obviously logical and
efficient after the discovery ofthe unpainted tips. All additions would be
built onto the mahogany without disturbance to the poplar panel. After
the cradle was removed and the back scraped clean, a track was routed to
halfthe thickness of the mahogany, and new mahogany pieces were fitted
to extend that plane to accommodate the fragments, including their pro-
truding tips (Figs. 16, 17). After the exact placement of the fragments was
decided, the areas that were completely missing would need to be built up
from the mahogany to the level of the gesso preparation (see Figs. 8, 9).
Very old poplar brought from Italy was used for this purpose in order to
maintain a consistent structure (Fig. 18). After the poplar collar was glued
to the mahogany with a polyvinyl acetate (PVA) emulsion (Fig. 19), the
fragments were set into the cutouts in the collar and precisely aligned with
the surface of the main part of the panel, both along and across the grain.
Rabbit-skin glue thickened with calcium carbonate was used as an adhe-
sive to fill any gaps caused by adjusting for surface level. Other adhesives,
such as Ciba-Geigy Araldite 1253 carvable paste, have excellent gap-filling
properties as well as much longer curing times; however, the traditional350 Bisacca
Figure 16, below
Fitting of the mahogany extensions for the
Washington panel.
Figure 17, below right
Washington panel after the completion ofthe
mahogany additions.
Figure 15
Preliminary arrangement of all fragments.