The Structural Conservation of Panel Paintings

Consolidation and impregnation of

woodworm-affected areas

Where there are cases of woodworm attack, it is very difficult to consoli-

date the remaining wood, especially immediately behind the paint. The

worst cases of this may eventually lead to the necessity for a transfer.

Various materials have been tried in impregnation tests and evaluated for

their efficacy in penetration and consolidation, with Paraloid B67 in white

spirit found to be the most suitable. This material also could and would

act as a moisture barrier, in preference to the old methods of applying

Saran or hot wax. B67 and wood flour are used for infills of any large open

wormholes or lost areas. Very large losses would possibly be infilled with

wood similar to the original, with the grain running in the same direction

as that of the original.

Moisture barriers

To create a moisture barrier by means other than impregnation with

Paraloid B67 (for example), a layer of material preimpregnated with Beva

371 could be attached to the back of the panel with a warm spatula. This

technique can also give extra support to the panel, reducing the need for

further treatment.

Infills of balsa wood

Where it proves necessary to remove restricting bars, battens, butterfly

buttons, cradles, and so forth from the back of the panel, it is customary

to infill with a material such as balsa wood (Fig. 4), cut to half its depth

across the grain at 2.5 cm intervals to counter any tendency of its own

to move, and usually running parallel with the grain of the original.

Sometimes original chamfered sliding battens can be reduced a little, also

cut halfway through at 2.5 cm intervals, and reused.

Panel trays

Where the original panel is in a state too fragile to support itself, either

because of thinning or because of inherent weakness, it is often incorpo-

rated into a tray. The tray is a secondary support that has been used in the

National Gallery for a long time, although its construction and materials

have been improved and developed in recent years.

The panel tray consists of a backboard made up of Aerolam “F”

board (aluminum honeycomb covered in a resinated fiberglass) with the

internal edges cut back to allowthe inset ofa cedar strip (Brough and

Dunkerton 1984; Dunkerton and Smith 1986), the purpose of which is to

attach the panel tray to the outer oak frame, which is made to cap the

front edges of the picture (Fig. 5). In a tray, the picture is completely sup-

ported at the back on blocks (minimum 6 mm thickness) of either Evazote

(low-density polyethylene [LDPE] copolymer foam) or Plastazote (LDPE

foam), with at least 3 mm of the same material under the oak strip that

caps the sides and the edges. Evazote and Plastazote are available in

different densities, and the strip of Evazote or Plastazote at the bottom

ofthe tray frame supporting the picture should be of a higher density to

prev ent it from slipping down in the tray’s rabbet.

S C  P P   N G, L 407

Figure 4
Zanobi di Benedetto Strozzi, The
Annunciation,ca. 1450. Reverse. Tempera on
panel, cut on all sides, 103.5 3 141.6 cm.
National Gallery (NG 1406), London. On the
back of the panel, infills of toned balsa are
seen on the right side; balsa pieces ready for
fitting are on the middle and the left side.