about^5 / 8 [in.] in thickness. These blocks with adhesive were pressed by hand
onto the fabric surface in a brick-like pattern and allowed to cool. After cov-
ering the surface of the painting, the edges were trimmed and light hard-
wood strips were attached with the same adhesive to all edges. The back of
the construction was smoothed and a sheet of^1 / 8 inch Masonite was attached
to the back surface in the same adhesive. (Kolch 1977:46)This panel has remained stable and free from the insecurities that
had been chronic prior to the treatment.In 1952 Richard Buck established the Intermuseum Conservation
Association at Oberlin College. There he continued to refine the backing
methods. He and Delbert Spurlock used this end-grain balsa-block method
with more emphasis on backing and reinforcement, less emphasis on exca-
vation and reconstruction. The method also featured the inclusion of
fiberglass cloth embedded in Saran F310 resin between the panel back and
the block-and-wax backing. While this layer provided a moisture barrier, it
was also designed to function as a natural layer of separation that would
release if internal stress became too strong. This is possible because of a
relatively weaker bond between the Saran and wax layers. Warped panels
were generally backed in a relaxed state, with the backing conforming to
the warp. Buck has reported that over the period from 1952 to 1970, the
treatment of some fifty paintings in this manner greatly reduced or elimi-
nated paint instability (Buck 1970, 1972).
The details of the balsa-block backing used at Oberlin are
described elsewhere (Spurlock 1978), so the method will only be described
here briefly (Figs. 6–10). All extraneous elements are removed from the
back surface, and the exposed wood is coated with Saran F310 resin.^1 A
layer of open-weave fiberglass cloth is adhered with a second coating of
Saran resin. The balsa blocks are cut across the grain and attached with
a wax-resin mortar made up of wax-resin bulked with wood flour and
kaolin. Strips of pine are often added across the grain of the panel at the
back surface of the balsa blocks as reinforcement. Finally, the back is
smoothed and coated with Saran resin and a finishing varnish.
Buck did not view this method as a recipe for the treatment of
all panel paintings but saw it, instead, as a method appropriate for many
cases. He recognized that details of the method can be varied without
compromise to the general principles. For example, the thickness of the
balsa blocks and the use of pine battens can be adjusted to suit the panel.
The Saran layer can be replaced with a more stable but less effective mois-
ture barrier such as Acryloid B72, or the wax can be applied directly to the
panel. Variations, however, should be considered in light of his summary
ofthe desirable attributes of this backing method: “In theory this treat-
ment combines the fav ourable aspects of the relaxed panel with those of
the system offixed mechanical control. The supplementary panel con-
tributes high moisture barrier efficiency to reduce the movement of the
original support, and imposes some mechanical restraint to persistent
swelling and shrinking. It stabilized warp near the point of minimum
normal strain. Although the applied panel has sufficient rigidity to serve
itspurpose, it possesses a degree of yield. The danger of panel rupture
from the rigid control is not eliminated, though I believe it is not high”
(Buck 1961:162).Balsa-Block Backing
at Oberlin294 Horns