the paint, the compression will be lessened. The intention of the balsa-
backing method is to introduce as much deformation in tension at the
back surface as possible. One of Buck’s favorite demonstrations was to
swell samples of wood and then glue battens to one side with their grain
running perpendicular to that of the samples. When the samples were
dried, the battens were removed, revealing a permanent warp due to the
restraint the batten provided to the shrinkage of one side of the sample.
Part of the intention offlattening with the balsa backing is to similarly
restrain the shrinkage of the back surface and allow for plastic deforma-
tion and relaxation of stress as the panel slowly dries to equilibrium. By
reduction of the warp with moisture and application of a balsa backing, it
is hoped that the reduced compression of the painted surface will result in
a panel with a minimum of elastic strain. Figures 12 and 13 show that it
may be difficult to eliminate compression at the paint surface during any
flattening with moisture. While strain gauge measurements on this sample
show that compression at the upper surface was somewhat less during
flattening with moisture than when the sample was simply clamped flat,
there is still substantial compression. As the moisture content was raised
past the point of initial flattening, this compression began to decrease
(Fig.14). Buck’s description of the flattening and balsa backing includes
just such an extended exposure (Buck 1972:8). This approach could help to
reduce the risk of permanent compression being introduced at the paint
surface. The individual circumstances of each flattening operation make
the conditions at the paint film uncertain, however. There are risks with
anyflattening operation, and such treatments should be approached with
the greatest caution.Perhaps the most appropriate use of the balsa-backing method is for paint-
ings that have a history of insecurity and that will be exposed to a poorly
controlled environment. In the author’s experience with balsa backings,
panels show good stability after treatment, as well as a reduced susceptibil-
ity to movement and insecurity. One case in particular seems to illustrate
this point. This panel is privately owned and has been subjected to the
rather severe environmental fluctuations of a northern climate. The panel
was brought to Minnesota in 1977 and immediately developed extensive
tenting of the paint during the first winter. Previous losses indicated that
this had been a chronic problem. A cradle (perhaps fairly recently applied)
was present. It was restraining the panel in such a way that a slight con-
cave warp developed. When the cradle was removed, the relaxed panel
took on a slight convex warp. This warp was retained when the balsa back-
ing was applied. In the years since the treatment, there has been no new
flaking in the original paint, although recent examination found a small
area offilling that had loosened. The owners indicate that some move-
ment ofthe panel from season to season is visible in relation to the frame
edge, but this has not been measured precisely.
Similarly, the balsa backings done at Oberlin of which the author
is aware have shown good stability. There is one instance in which a
mechanical problem led to a precipitous drop in RH in a gallery. Several
panels developed tenting and insecurity in the paint, but two panels
backed at Oberlin showed no adverse effects.
Although the elastic and plastic aspects ofdeformation are not
easily separated, their presence has much to do with the treatment ofSummary
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