degree of plasticity due to the gradual drying under restraint from the
backing. Furthermore, Buck felt that although the balsa backing itself
might tend to react to environmental fluctuations slightly, it would, never-
theless, provide some restraint to the movement of the panel, thereby
reducing the stress imposed on the paint film(Buck 1963:162).
The uniform balsa backing can provide a stable support that
resists warping from environmental exposure or from the release of unde-
tected elastic strain. In addition, in future cycles of moisture change, this
restraining backing may reduce some internal elastic strain, a factor that is
particularly significant when the reduction of a warp is involved. In such
cases it is anticipated that the restraint of the backing during the initial
drying of the flattened panel and during subsequent cycles may allow a
form of mechanosorptive relaxation to establish an increased internal sta-
bility in the wood structure.
It seems clear that the use of a uniform backing—and in particu-
lar the balsa-block method—has a history of success and is an important
treatment option.Use of the records and photographs from the Fogg Museum Laboratory,
as well as permission to use unpublished material compiled by David
Kolch, is through the courtesy of the Straus Center for Conservation,
Harvard University Art Museums.1 Saran F310 resin is soluble in methyl ethyl ketone for brushing.
2 For this sample, a 2 mm thick sheet ofLexan polycarbonate was attached with clear epoxy
resin. In this sample, the author used an SR-4 model strain gauge (BLH Electronics).Acryloid B72,Rohm and Haas Co., Independence Mall Street, Philadelphia, PA 19105;
Conservation Materials, Ltd., 100 Standing Rock Circle, Reno, NV 89511.
Clear epoxy resin,Devcon Consumer Products, 264 Howard Ave., Des Plaines, IL 60018.
Le xan polycarbonate,(General Electric) Cadillac Plastic and Chemical Co., 1218 Central Ave.
N.E., Minneapolis, MN 55414.
Materials specifically designed for photoelastic stress analysis,Photoelastic Division,
Measurements Group, P.O. Box 27777, Raleigh, NC 27611.
Saran F310 resin,DowChemical Co., Main Street, Midland, MI 48674.
SR-4 model strain gauge,BLH Electronics Inc., 75 Shawmut Rd., Canton, MA 02021.
Strain gauges, Micro-Measurements Division, Measurements Group, P.O. Box 27777,
Raleigh, NC 27611.Armstrong, L. D., and G. N. Christensen
1961 Influence of moisture changes on deformation of wood under stress.
Nature191:869–70.Barkas, W. W.
1949 The Swelling of Wood under Stress.London: Her Majesty’s Stationery Office.Buck, Richard D.
1947 Reclaiming a Flemish painting. Bulletin of the Fog g Museum ofArt 10:193–207.References
Materials and Suppliers
Notes
Acknowledgments
R B: T D U B B P P 301