Restoration of the frame and elastic tensioning of the painting on canvas “Immacolata Concezione” by Giuseppe Peroni (1771) at the Church of San Filippo Neri in Turin
During the restoration of the canvas, the frame was disassembled by removing the 18th century nails, some of which were driven through and riveted at the intersections of the joints.
In order to transport it, it was necessary to dismantle the vertical crosspiece jointed at half thickness into two parts. Transferred to the laboratory, the cross beams were dusted and then cleaned with a solvent solution calibrated through preliminary tests. The wood was then treated with a consolidation solution consisting of methyl ethyl ketone with the addition of pure permethrin as a woodworm repellent.
In order to achieve elastic tensioning, the original frame had to be slightly modified. First of all, weak or fractured areas were restored and then glued and pivoted (walnut pins).
In particular, these operations were carried out in the area of the central half-thickness joint of the second horizontal crossbar from below, which was very fragile and had broken during disassembly, and on the two joints of the rib impost with the horizontal crossbar. Both joints, tenon and mortise, were broken or completely absent, and the only thing holding them together was the vertical doubling element of the frame. These joints were strengthened and made integral with the rib by wooden reconstructions and specific restoration adhesives.
Wooden battens with a rectangular cross-section were applied around the entire perimeter. One side of the laths has two rounded edges and was coated with Teflon adhesive (a 0.125 mm glass fibre fabric impregnated with PTFE) and the laths were then screwed to the perimeter rods of the frame. The result is twofold: the canvas is spaced away from the frame avoiding contact, it creates a perimeter with very low adherence allowing the perimeter strips to slide and finally it regularises the perimeter of the work.
On the back of the frame are mechanisms for the springs. The mechanisms have a low visual impact and are made up of three main elements: the drilled rod for adjusting the threaded pin that brings the spring into tension, the stainless steel spring with German-style eyelet and tapering to hold the head of the threaded rod and with a predefined elastic K. Finally, the pin with the small pulley that allows the steel cable to be deflected and thus the tensile force. The cable is a 30-pound heat-sealed braided steel wire, which was tightened either by heat welding or by aluminium sleeves. A 5 mm diameter stainless steel rod was used to distribute the force on the perimeter strips. The bars were inserted into slots on the perimeter strips of the edge lining sewn with polyester thread.