The Structural Conservation of Panel Paintings

of the false tenons—and, hence, of the mortises made in the original sup-

ports as well.

Over the centuries, certain original joint assemblies, because of

technical developments such as pegged false tenons and tongue-and-

groove joints, have caused serious alterations to the paint layer. In such

cases, their readjustment or modification seems necessary when the joint

is repaired. Thus, for example, in the case of pegged false tenons, where

the pegs generate splits, the staffremoves some of those pieces, working

from the back ofthe panel. This procedure eliminates the constraints

caused by the initially blocking joint and allows the false tenons to move

in the mortises when the wood undergoes dimensional changes.

Sometimes there is a need to first consolidate the structure of a wood

badly weakened by various assaults. This brings up the problem of choos-

ing a consolidant (taking into account its viscosity, reversibility, and aging

properties) as well as the problem offinding a method of treatment aimed

at preventing an overly heterogeneous consolidation that would cause

areas of different rheological behavior to develop.

Consolidation is currently achieved with an acrylic resin, Paraloid

B72, usually dissolved in toluene and usually applied by injection, brush-

ing, or, should the panel so permit, by capillarity. Since, given the present

state ofknowledge, it is not always possible to diagnose the extent and

effectiveness of the treatment, it is important to limit as far as possible the

penetration of the consolidant into the material—especially considering

that its reversibility is not total. It would be very interesting, in the future,

to be able to measure the product’s degree of penetration and its cohesive

strength inside the work.

Accidental lacunae in the wood are filled with a material chosen

according to several criteria: the state of conservation of the support, the

localization of the lacunae, their influence on the structure, and their aes-

thetic impact.

Small lacunae arefilled with an emulsion ofpolyvinyl acetate in

50% water mixed with sawdust or mechanically reversible Master Model

Paste.^16 Alarge lacuna—after precise measuring and cutting that carefully

respects the integrity of the work—is generally filled with a piece of wood

ofthe same grain and species, inserted at a slightly lower level than the

original wood. For severely worm-eaten panels whose density has been

reduced considerably by insect tunneling or for areas not requiring any

special mechanical property, the staffprefers to use balsa wood. And for

very weak, seriously thinned-down panels, structural cohesion is reestab-

lished by backing of their surfaces.

Aspecific r estoration problem was posed by nineteenth-century

works painted on supports that were composed of several strata of wood

artificially held together. The best-known example was developed in 1845

by Tachet; he devised a method of gluing three crossed sheets with shel-

lac, which was sprayed on and then heat sealed in order to reduce the

wood’s movement. However, with time, the glue weakened, the support

loosened, and cracks appeared on the paint layer. The restoration method

that has been developed to address such supports attempts to reconcile the

necessities for recovering cohesion of the support, maintaining reversibil-

ity, and preserving the work’s aesthetic appeal. It consists of replacing the

thick central core with a thin sheet of plywood^17 and an interlayer of

Reestablishing the Panel’s

Structural Cohesion

256 Bret, Jaunard, and Mandron