a secondary support to the back, which will normally return the panel to
its original thickness or even make it slightly thicker.
This procedure used to involve an updated and improved form of
a method—the balsa-wood and wax-resin cement buildup—introduced
from the United States by Richard Buck in 1949. This method has been
described in the National Gallery Technical Bulletin (Smith, Reeve, and
Ashok 1981) (Fig. 6). Since then, the method has been improved by the use
of a different materials as an interleaf—impregnated with Beva 371 on
both sides—between the original panel and the buildup, thereby prevent-
ing impregnation of the wax-resin into the original panel. Also, the balsa
planks are all sawed halfway through at 2.5 cm intervals after the applica-
tion of each layer, in order to reduce their strength (Fig. 7).
The application of the modified version of a balsa-wood panel
buildup begins after moisture treatment or flattening, where necessary.
New refinements ofthe method using the multipurpose low-pressure table
are described in the case study below.Transfers
Transferring a painting is the last resort and is considered only when the
support or ground is no longer able to maintain the painting. Methods
vary according to the problem. The only example carried out at the
National Gallery in recent years was the transfer ofThe Incredulity ofSaint
Thomas(NG 816) by Cima da Conegliano (1459–1517), in which the fol-
lowing procedure was employed (Wyld and Dunkerton 1985).
After removal of the remaining wood and consolidation ofthe
ground from the back, a reversible isolating layer of acrylic primer was
applied, followed by a vinyl emulsion filler. An interleaf offinely woven
white linen stretched on a loom was coated on both sides with a synthetic,
heat-bonded adhesive (Beva 371) and attached to the reverse of the paint
and ground. This was, in turn, attached to an aluminum honeycomb
epoxy-coated fiberglass board (Aerolam “F” board), also coated with Beva- The author has found it more aesthetically pleasing to use a slightly
textured surface for these supports; a flat texture seems to impose an
unnatural smoothness.
Panel fittings
For support, early panels or fragments may need specially designed brack-
ets of metal or other material, lined with polyethylene foam or velvet, so
that no fixings are applied into the original panel. The security of the
object must also be a consideration in the design ofthe brackets.Frame fitting and exhibiting
Apicture should be put into the frame against a soft surface of velvet or
similar material to prevent scuffing of the edges. Panels that are warped
need shaped polyethylene foam strips between them and the rabbet. In
order for the foam strips not to become compressed at the base of the
panels, they must be made of a higher density polyethylene or of balsa
wood. Panels should be held in frames with as fewfittings as possible, with
adequate flexible polyethylene pads between the fittings and the panel.
The fittings should also be placed at the ends ofthe wood grain only—
atthe top and bottom for vertical grains and at the sides for horizontalS C P P N G, L 409