that rub against each other. Last, their mechanisms must not be too com-
plex for simple maintenance.
Three types of maintenance systems have been developed for
application to the reverse of panels. They are (1) reinforcement systems
that replace original elements on the reverse of panels, (2) maintenance
systems that offset significant loss of cohesion of original supports, and
(3)backing systems that consolidate overly thinned supports.Reinforcement systems that replace original elements on
the reverse of panelsThese systems are used in cases where there is no risk that the weight or
tension they exert could deform the support—that is, they are designed for
supports that are sufficiently sturdy or structured. The most widely used
system ofreinforcement involves sliding crosspieces, or runners. Adapted
to the curve of the panel, they are composed of pieces of mahogany fitted
on both edges with U-shaped metallic bands into which slide Teflon or
brass rollers attached to wooden cleats that are themselves glued to the
original panel in the direction of the grain. The current trend is toward
reducing the thickness of these crosspieces in order to make the whole
construction lighter and more flexible.Maintenance systems that offset significant loss of
cohesion oforiginal supportsThese systems are used on panels whose structure is fragile because of
their thinness or because of severely deteriorated areas. They are based on
a perimetric maintenance of the object, either byfitting of the frame with
a rabbet into which the painting will be positioned or by the assembly of
such structures as the châssis-cadre,a modern version of the grooved struc-
tures into which the panels of the Nordic schools of the fifteenth and six-
teenth centuries were imbedded and which surprise us still by their quality
of conservation. Such a system is composed of a fitted wooden frame to
which is screwed an L-shaped brass cornice that reinforces the perimeter
of the painting (Fig. 5a, b); enough space is left to allow for expansion and
retraction of the wood. It should be noted that the panel does not support
the weight of the châssis-cadre. For large panels this system can be com-
bined with sliding runners attached to the frame.
The current trend in stretcher-frame fabrication is toward
enhanced flexibility and capacity to follow the dimensional variations of
the panels. First, to lighten it, the frame is hollowed out slightly with a
cylindrical bit. Insertion of a system of springs into some of the cavities
thus created enables the panel to move in three directions, rather than
exclusively in a line. The same result is obtained by replacing the frame’s
sliding runners with plain perforated crosspieces connected to the support
by means of cleats equipped with springs (Figs. 5a, 6a, b); this also reduces
the mechanical leverage effects produced by the traditional lateral arrange-
ment of cleats with rollers. The L-shaped metal cornices are made some-
what less rigid by evenly spaced sections cut into the narrow side that is
screwed onto the frame (Fig. 5b). Finally, to reduce friction, the inside
faces of the frame are lined with Teflon.
In certain cases it will be necessary to replace the wooden frame
with a sheet ofAltuglass to allowan unobstructed reading of the two258 Bret, Jaunard, and Mandron