a smooth, flat surface to aid movement, reducing the risk that the panel
would stick in the frame rabbet or tray. Free movement was further
improved by using Teflon/PTFE (polytetrafluoroethylene) pressure-
sensitive adhesive tape^6 to line the rabbet.
Upon completion, the support lattice was attached to the panel
byengagement ofthe flexible strips in position in the retaining blocks
(Fig. 5). When this procedure was done, the panel tended to flatten out
slightly and, when handled, could be felt to be appreciably less flexible
than before the auxiliary support was in place.Monitoring panel warp
At this stage, the slip profile was considered. Assuming that enough time
has been available, the panel should preferably have had its end-grain
profiles monitored and recorded three times during cycles of RH—initially
with whatever cradle or restriction was in place when the panel arrived for
treatment; again, with restrictions removed and the panel totally free to
respond; and, finally, with the new support attached. This profile would be
expected to fall somewhere between the first two recorded profiles.
Consideration should also be given to simulating the conditions
under which the panel is going to be displayed in the future. In some
countries the extremes of RH may be outside of the limits normally
used in a monitoring cycle (i.e., 40–80% RH). After the slip profile has
been determined by monitoring under appropriate conditions^7 with the
support attached, some thought can be given to the depth of the tray or
rabbet. This depth needs to be sufficient to accommodate the anticipated
extreme limits ofmovement of the panel; it should also be adequate for
the spring bridge supports, which will be used to hold the assembly in
place within the frame.Back springs
The principle of using back springs was conceived by Simon Bobak (see “A
Flexible Unattached Auxiliary Support,” herein) for use on unattached sup-
ports. It consists of individual flexible battens, each attached by a centerT D F A A S 389Figure 5
Back of sixteenth-century Flemish oak panel
(first case study), 1.2 3 1.7 m, after structural
conservation, with flexible auxiliary support
engaged, providing reinforcement.