panel, in order to lessen the friction of wood against wood.^73 In the system
of cylindrical steel crossbars used from 1967 to 1969, the crossbars slide
incleats sheathed with brass; friction is therefore limited to those areas.
Finally, crossbars of H-shaped cross section, made of an aluminum alloy,
began to appear in 1967. After 1970 these are sometimes reinforced by
Bakelized wood or mahogany; this system limits friction to the small Teflon
rollers that allow the metal crossbars to slide easily (Emile-Mâle 1976:113).
There was a gradual attempt to eliminate crossbars and the use
ofadhesives; by 1969 this progression resulted in a simple perimetric rein-
forcement: the châssis-cadresystem. This device is formed of an L-section
brass perimeter stretcher, lined with felt on the side of the painting, or
formed ofa frame of mahogany or Permali, possibly shaped to fit the
warp of the panel and spaced 2–3 mm from the panel to allow for the pos-
sible expansion of the wood. Adhesives are no longer used, and there is a
minimum offriction.
Avariant of this procedure features a mobile backing in acrylic
resin (Altuglass). First used as a flat sheet in 1970,^74 this type of backing
was then contoured to follow the warp of the painting as of 1974. This
system replaced the châssis-cadre system, with the Altuglass taking the
place of the stretcher; it allows a thin, fragile, and locally brittle painting
to be supported; weak areas of the panel can be reinforced with a local
restraining cleat through the Altuglass. The advantage is a transparency
that allows all the information on the back of the work to be read. The
major drawback is the considerable weight of the whole.
When the picture is too thin to justify a châssis-cadre but too big
to allow a mobile backing, a modified châssis-cadre can be prepared,278 Bergeon, Emile-Mâle, Huot, and Baÿ
Figure 12
Cima da Conegliano, La Vierge et l’Enfant.
Reverse. Louvre Museum (RF 2100), Paris.
The wooden support of this painting, which
was formerly thinned, is worm-eaten and
split. After the old cradle was removed, it was
disinfected and its fractures were reduced by
incision and V-shaped inlays.
Figure 13
A rigid support plate of acrylic resin
(Altuglass), shaped to follow the warp
of the panel, in the treatment of Cima da
Conegliano’s La Vierge et l’Enfant.