Structural Conservation of Panel Paintings 306

PART FOUR Current Approaches to the Structural Conservation of Panel Paintings 306 Florentine Structural Stabilization Techniques Andrea Rothe and Giovanni Marussich by the great flood of 1966 in Florence than by both World Wars combined. Many paintings Mand other artifacts were submerged in the floodwaters for more than eighteen hours. They were covered with mud mixed with heavy deposits of heating oil that had seeped from the storage tanks housed in the many basements of the city.The worst damage was done to the large num- ber of panel paintings in Florence and the surrounding countryside; those that had been submerged swelled many inches beyond their original size. Subsequently, these paintings were subjected to a long and gradual drying process, first in the limonaia, the old hothouses built by the Medici in the Boboli Gardens for their favorite collection of citrus plants. These hothouses were quickly converted into one large humidity chamber. The humidity was raised to 95% at a temperature of 12 °C over a two-year period. Afterward, the treatment was continued in the former army bar- racks of the Fortezza da Basso, which in the meantime had been trans- formed into the largest restoration laboratory in the world; it had, in fact, become an independent governmental department, a soprintendenza, by special decree. Despite the carefully controlled drying process, many of the panels shrank considerably. This shrinkage caused severe blistering and cupping of the paint layers, as well as deformation of the supports (Cianfanelli, Ciani Passeri, and Rossi Scarzanella 1992). Consequently, many of the panel paintings had to be transferred to canvases and to new, rigid supports. The oil deposits were removed with a poultice made from Shellsol A and talc applied to a Japanese-tissue interleaf. The devastation caused by the flood was, to some degree, offset by the benefit of the better understanding that was gained about the behavior of wooden artifacts—panel paintings in particular. For instance, the negative effects of dovetails, which had already gone out of style by the end of the 1950s, were confirmed (see Rothe, “Critical History,” herein). The negative effects of rigid restraints or crossbars in relation to the natural flexibility of panels were better understood. It became clear that those restraints that held the panels in place but did not hinder their need to expand and contract were the most effective. It also became obvious that the materials that were used for crossbars had to be stable and unaffected by environmental fluctuations. Mansonia, which had been widely used in Florence by the restoration F S S T 307 departments of the Vecchie Poste at the Uffizi and Palazzo Pitti before the flood, proved to be the most stable wood, with the least tendency to deform (see Rothe, “Critical History,” herein).1 Used for more than forty years in the construction of crossbars, mansonia functions very efficiently and, in fact, appears to be better than any other type of wood because of its density and workability. Panels with mansonia crossbars expanded and contracted drastically after the flood but did so with little or no buckling. Planks of mansonia that had been immersed for over a week and then inadvertently used as gangways to wheel mud out from the ground floor of the Vecchie Poste did not deform or crack, and they were later utilized to make new crossbars. Today mansonia is still used—although much less often because of its toxic properties. Other woods, such as steamed beech, have also been used but have not given such satisfying results. Metal crossbars, such as those used successfully in Rome by the Istituto Centrale del Restauro, have rarely been used in Florence, primarily because of aesthetic considerations (see Rothe, “Critical History,” herein). If a panel is in good condition, the conservator usually chooses not to intervene. Unfortunately, this is not always possible. Intervention is necessary whenever the original crossbars have been lost (causing warpage), the panel has previously been thinned, splits have caused loss of color, or panels have cracked apart. The restraint that a brace or crossbar should exert on a panel is difficult to measure or predict, but today the rule is to give the panel ample lateral freedom to move and to manipulate the original surface as little as possible by making the braces much smaller than was formerly considered appropriate, and thus more flexible (Figs. 1, 2). Excessive restraint such as that caused by older cradles tends to block the movement and facilitate the formation of new cracks and even of splits (Figs. 3, 4). Conversely, too little restraint can allow panels to deform, especially those that have been thinned and have lost their original coating (see Rothe, “Critical History,” herein) or the aged “skin” that Figure 1 Guglielmo di Pietro de Marcillat, Annunciation, 1524. Reverse. Oil or mixed technique (?) on panel, 180 ϫ 150 cm. Convent of S. Francesco, Sargiano, Arezzo. A typically heavy crossbar of the early 1970s, with pegs glued and screwed to the panel; a wide swath of original wood surface was removed to create a level area. The crossbar on the bottom is original. 308 Rothe and Marussich Figure 2 Examples of crossbars showing progressive e reduction in size. (a) Crossbar used in 1975 on the Annunciation by Guglielmo di Pietro de Marcillat, Convent of S. Francesco, Sargiano, d Arezzo; the panel is 150 cm wide, the crossbar 7.5 cm wide. (b) Crossbars used in 1988 on the Nativity by Girolamo di Benvenuto, The J.Paul Getty Museum, Los Angeles; the panel is 161 cm wide, the crossbars 4.5 cm wide. c (c) Crossbars used in 1989 on The Birth of Bacchus by Giulio Romano, The J. Paul Getty Museum; the panel is 80 cm wide, the crossbars 3.2 cm wide. (d) Crossbars used in 1987 b on The Card Players by Joos van Crasbeeck, The J. Paul Getty Museum; the panel is 31.1 cm wide, the crossbars 2.7 cm wide. (e) If f crossbars were to be placed on The Card Players today, a smaller version (1.8 cm wide) would be used. (f) Crossbars used in 1990 on The Abduction of Proserpine by Alessandro a Allori, The J. Paul Getty Museum; the panel is 228 cm wide, the crossbars 3.3 cm wide. Figure 3, below Girolamo di Benvenuto, Nativity, ca. 1500. forms on the back of old panels (consisting primarily of compacted wood Reverse. Tempera on panel, 204 ϫ 161 cm. cells and accumulated dirt). The J.Paul Getty Museum, Los Angeles.A In the Florentine approach to rejoining panels, the precision with heavy cradle is glued to the panel, which had which the work is carried out is key to the success of the treatment. This been thinned to less than 12 mm. This intervention dates to about 1900. approach is described as risanamento delle tavole, “making panels sound again.” The pivotal task is to cut precise V-shaped grooves of approxi- Figure 4, above Girolamo di Benvenuto, Nativity. Detail. This raking-light photograph shows distortions and cracks on the surface caused by the thinning of the panel and the restraint of the heavy cradle. F S S T 309 Figure 5 Some tools used in the preparation of V-shaped grooves. mately 55°. The groove should straddle the crack all the way down to the gesso preparation; short, individually fitted wedges are then inserted into these grooves. The grooves should be made as deep as possible without causing damage to the paint layer, so as to avoid the formation of hairline fissures (see Rothe, “Critical History,” herein). The type of wood used to reconstruct these panels should be well- aged material of the same type as the original painting support. The vari- ous chisels used, including a pointed chisel for the finishing of the V-shaped grooves, must be maintained in constant sharpness (Fig. 5). If percussion is needed, the ball of the hand (never a mallet) may be used. In some instances, when the cracks are straight and long, two angled planes are used—one for the left side of the split, the other for the right side (Fig. 6). Before the wedges are inserted, the detached sections of the panel must be perfectly flush with each other. This is accomplished by a simple system of temporary braces, or tiranti, that are screwed into the panel Figure 6 Two angled planes, sometimes used for preparing long, straight grooves. 310 Rothe and Marussich wherever necessary along the crack. By strategic placement of the screws and the small blocks under the braces, either side of the split can be pushed down or pulled up (Fig. 7). If the panel is very thin, little blocks of wood can be temporarily glued onto the panel to hold the screws in the areas that need to be leveled. The glue used for softer woods, such as poplar and limewood, is mostly a polyvinyl acetate (PVA) emulsion glue such as Vinavil, thinned with water.2 Woodworkers point out that the glue that oozes out is what ensures a lasting bond—meaning that the less glue that remains between the wedge and the wood of the panel, the better. For harder woods such as oak, a two-component epoxy glue such as Araldite is used.3 For those who are not master artisans, a simpler and quite effective method was developed by Barbara Heller at the Detroit Institute of Arts after she worked for many years in Florence (Heller 1983). She cuts the grooves with a router and uses precut V wedges that are set in with Araldite carvable paste.4 The results have been very encouraging and seem to be stable, especially in the case of softer woods such as poplar.

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