554 Richard, Mecklenburg, and Tumosa
Temperature variations during transit should be minimized by use
of climate-controlled vehicles and thermal insulation inside packing cases.
Table 5 gives the typical glass-transition temperatures for three types of
paint. However, paintings should never be subjected to temperatures as
low as these values and, ideally, should stay above 10 °C.
Careful attention should be given to the selection and proper use
ofcushioning materials in the packing cases to ensure that paintings are not
exposed to edge drops resulting in forces exceeding approximately 40–50 G.
For panel paintings, topple accidents can cause more severe dam-
age than edge drops. The edges of panel paintings should be supportedTable 3 Maximum allowable RH ranges and relative risks for well-attached gesso applied to
unrestrained white oak panels in different grain orientationsPanel grain Equilibrium RH Allowable RH
orientation (%) range to yield (%) Relative risk
Longitudinal 50 20–86 low
Radial 50 22–79 low
Tangential 50 33–62 medium
Longitudinal 64 29–93 low
Radial 64 33–87 low
Tangential 64 53–68 high
Longitudinal 70 32–96 low
Radial 70 32–84 low
Tangential 70 65–73 very high
Longitudinal 36 12–75 low
Radial 36 15–71 low
Tangential 36 26–54 mediumTable 4 Maximum allowable RH ranges and relative risks for well-attached oil paint applied to
unrestrained white oak panels in different grain orientationsPanel grain Equilibrium RH Allowable RH
orientation (%) range to yield (%) Relative risk
Longitudinal 50 8–95 low
Radial 50 13–86 low
Tangential 50 27–65 medium
Longitudinal 64 16–95 low
Radial 64 20–92 low
Tangential 64 43–71 medium
Longitudinal 70 17–95 low
Radial 70 19–90 low
Tangential 70 61–75 very high
Longitudinal 36 4–92 low
Radial 36 8–88 low
Tangential 36 22–60 mediumTable 5 Approximate glass-transition tem-
peratures for selected paints
Glass-transition
Material temperature, Tg(°C)
Oil paint 210
Alkyd paint 25
Acrylic paint 15