T C T P P 553ful. These cases come in various sizes and shapes, the smaller ones fitting
conveniently under aircraft seats. The procedure for packing a painting in
these cases is straightforward. The National Gallery of Art in Washington,
D.C., often follows these steps: First, either the framed panel painting is
wrapped directly in polyethylene and sealed with waterproof tape, or it is
placed in an inner case that is wrapped in polyethylene. Unframed panels
are always fitted into an inner case to prevent anything from touching the
surface ofthe painting. The metal photography case is then filled with
polyester urethane foam. A cavity is cut into the foam with a minimum of
2.54 cm of foam remaining on all sides. In this cavity, the wrapped painting
or inner case is placed. In this procedure the polyester urethane foam func-
tions as both cushioning material and thermal insulation.Most panel paintings that are in good condition and free to respond
dimensionally to environmental variations can be safely transported, as
long as they are packed properly. However, there are circumstances when
some paintings are at greater risk than others. Therefore, all panels should
be carefully examined and an assessment should be made of RH- and
temperature-related stresses that may develop from improper framing
techniques or from restraint imposed by cradles or battens. Existing
cracks in the design layers usually act as expansion joints, but cracks in
panels can prove to be a potential problem, especially if the painting is
subjected to impact.
It is also important to compare the RH levels where the painting
normally hangs to the RH levels at the borrowing institution. If there is a
large discrepancy in the RH, a microclimate display case could be used.
Tables 2–4 summarize the relative RH-related risks f or sample paintings of
different construction and grain orientation. For example, Table 2 shows
the risks oftransporting a restrained, tangentially cut, white oak panel
that has been equilibrated to 70% RH or higher.
Tables 3 and 4 show that it is potentially hazardous to ship a panel
painting that has been equilibrated to 70% RH or higher and that has a
gesso ground or paint directly applied to the wood—particularly if the
wooden support is tangentially cut and not restrained.
To maintain stable moisture contents, paintings should be
wrapped in moisture-barrier materials, provided they are not already con-
ditioned to an unusually damp environment. Because condensation can
occur when paintings acclimated to very high RH are transported in
extremely cold weather, such transport could encourage mold growth.Conclusion
Table 2 Maximum allowable RH ranges and relative risks for sound, uncracked, and restrained
white oak panels in different grain orientationsPanel grain Equilibrium RH Allowable RH
orientation (%) range to yield (%) Relative risk
Tangential 36 25–54 medium
Tangential 50 33–63 low
Tangential 70 62–73 high
Radial 50 23–75 low
Radial 70 40–85 low